Reference values of 25-hydroxyvitamin D revisited: a position statement from the Brazilian Society of Endocrinology and Metabolism (SBEM) and the Brazilian Society of Clinical Pathology/Laboratory Medicine (SBPC)

ABSTRACT

Hypovitaminosis D is a common condition with a negative impact on health. This statement, prepared by experts from the Brazilian Society of Endocrinology and Metabolism and the Brazilian Society of Clinical Pathology/Laboratory Medicine, includes methodological aspects and limitations of the measurement of 25-hydroxyvitamin D [25(OH)D] for identification of vitamin D status, and identifies individuals at increased risk for deficiency of this vitamin in whom 25(OH)D measurement is recommended. For the general population, 25(OH)D levels between 20 and 60 ng/mL are considered normal, while individuals with levels below 20 ng/mL are considered to be vitamin D deficient. This statement identifies potential benefits of maintaining 25(OH)D levels > 30 ng/mL in specific conditions, including patients aged > 65 years or pregnant, those with recurrent falls, fragility fractures, osteoporosis, secondary hyperparathyroidism, chronic kidney disease, or cancer, and individuals using drugs with the potential to affect the vitamin D metabolism. This statement also calls attention to the risk of vitamin D intoxication, a life-threatening condition that occurs at 25(OH)D levels above 100 ng/mL

Vitamin D; 25-hydroxyvitamin D; reference range; vitamin D intoxication

INTRODUCTION

Hypovitaminosis D is highly prevalent according to international and Brazilian studies, independent of the region evaluated ( ¹ , ² ). However, the prevalence rates of this condition vary according to the reference values established for 25-hydroxyvitamin D [25(OH)D], the metabolite measured to determine the vitamin D status ( ³ ).

In 2010, the US Institute of Medicine proposed an increase in the daily recommended amount of vitamin D for healthy adults from 200 IU to 600 IU. The Institute also considered 25(OH)D concentrations < 20 ng/mL to be potentially harmful for the general American population ( ⁴ ). Shortly after that, the Endocrine Society established the value of 30 ng/mL (instead of 20 ng/mL) as the lower limit of normal for 25(OH)D levels ( ⁵ ). Based on publications by these two institutions, along with review of national and international literature, the Brazilian Society of Endocrinology and Metabolism ( Sociedade Brasileira de Endocrinologia e Metabologia – SBEM) established in 2014 the 25(OH)D concentration of ≥ 30 ng/mL as desirable for populations at risk of harmful consequences from hypovitaminosis D ( ³ ). Since then, many studies on the effects of vitamin D supplementation have been published. At the same time, an intense debate has developed around the establishment of reference values for 25(OH)D, and new guidelines have emerged proposing levels between 20-30 ng/mL ( ⁶ - ⁹ ). This discussion prompted a review of the topic in 2017 by SBEM along with the Brazilian Society of Clinical Pathology/Laboratory Medicine (SBPC/ML) ( ¹⁰ ). Considering new evidence that has emerged since the review, the aim of this article is to present a critical evaluation of the current methodology for 25(OH)D measurement, report the groups most susceptible to the deficiency, and identify clinical situations in which low vitamin D concentrations are harmful and, thus, 25(OH)D levels above 30 ng/mL are recommended. A secondary objective of this article is to discuss the upper limit values of 25(OH)D that are deemed safe and the risks and causes of vitamin D intoxication.

Importantly, this document is intended to be a guide for clinicians dealing with specific populations and was written by a task force comprising experts from both societies who, by interpreting the scientific evidence in light of their broad research and clinical experience, contributed with their undeniable expert opinions. These concepts may change as new evidence emerges.

METHODOLOGICAL ASPECTS OF 25(OH)D MEASUREMENT

Vitamin D comprises a group of fat-soluble secosteroids. In humans, vitamin D₃ (cholecalciferol) is produced mainly in the skin from exposure of 7-dehydrocholesterol to type B ultraviolet radiation (wavelength 290 to 315 mn) from sunlight. In plants and fungi, vitamin D₂ (ergocalciferol) is synthesized by the action of ultraviolet radiation on ergosterol. Both vitamins D₃ and D₂ are obtained from diet, mainly from the consumption of fatty fish, cod liver oil, egg yolk, wild mushrooms, and fortified products (milk, cereals, etc.), although compared with cutaneous production, the diet is a much less important source of vitamin D for the body ( ¹¹ , ¹² ).

Vitamin D₃ or D₂ is initially metabolized in the liver and converted to 25(OH)D by 25-hydroxylase (CYP2R1) enzyme activity. Subsequently, 25(OH)D undergoes a second hydroxylation in the kidneys, mediated by the enzymes 1α-hydroxylase (CYP27B1) and 24,25-hydroxylase (CYP24A1), producing the metabolites 1,25-dihydroxyvitamin D [1,25(OH)₂D] and 24,25-dihydroxyvitamin D [24,25(OH)₂D], respectively. 1,25(OH)₂D, the active metabolite of vitamin D, can promote bone reabsorption, stimulate intestinal absorption of calcium and phosphorus and inhibit urinary excretion of these ions. 24,25(OH)₂D is the main product of 25(OH)D catabolism, and its concentration correlates strongly with the concentration of 25(OH)D. In the bloodstream, 25(OH)D, 1,25(OH)₂D, and 24,25(OH)₂D metabolites circulate mainly (85%-90%) bound to vitamin D-binding protein (DBP) and, to a lesser extent (10%-15%), to albumin and lipoproteins. Only a small fraction (≤1%) of 25(OH)D circulates in a free form. The free fraction plus the albumin-bound fraction are collectively named “bioavailable fraction”, since 25(OH)D is able to easily dissociate from these albumin proteins due to low affinity, becoming available to act on target cells. In most cells, free 25(OH)D is believed to cross cell membranes by simple diffusion and without mediation by carrying proteins. In renal tubular cells, 25(OH)D linked to DBP can be internalized by endocytosis mediated by the megalin/cubulin complex present in cell membranes. Once in the cytoplasm, free 25(OH)D [or 25(OH)D dissociated from DBP, if internalized while linked to this globulin] is converted to 1,25(OH)₂D to further interact with intranuclear receptors ( ¹¹ , ¹² ).

Production of 1,25(OH)₂D is regulated by several direct and indirect mechanisms. 1,25(OH)₂D directly inhibits the activity of 1α-hydroxylase (CYP27B1), decreasing further production of 1,25(OH)₂D. Additionally, 1,25(OH)₂D suppresses the secretion of PTH by the parathyroid glands; since PTH is an inducer of 1α-hydroxylase (CYP27B1), this mechanism inhibits the activity of this enzyme indirectly. Increased levels of 1,25(OH)₂D also stimulate renal production of fibroblast growth factor 23 (FGF-23; a phosphaturic factor), which in turn inhibits the activity of 1α-hydroxylase (CYP27B1). Finally, some studies suggest that the dietary intake of calcium and phosphorus can also suppress the expression of this enzyme ( ¹² ).

25(OH)D is the main vitamin D metabolite, and its measurement is considered the best indicator of the vitamin D reserve in the body. Due to its relatively long half-life (2-3 weeks), the circulating levels of 25(OH)D show little fluctuation, reflecting the combination of dietary intake and cutaneous vitamin D production ( ¹² , ¹³ ).

The main techniques for measurement of 25(OH)D are ligand assays and chromatographic methods associated with ultraviolet detection or tandem mass spectrometry ( ¹² - ¹⁴ ). Most laboratories use binding assays since these assays involve methods that are generally automated, inexpensive, fast, and easy to perform ( ¹⁵ ). These assays include a first step in which 25(OH)D is dissociated from its carrier proteins. In a second step, the 25(OH)D in the sample competes with an analogue for the same sites of the ligand’s assay [anti-25(OH)D or DBP antibodies]. Either the analogue or the ligand is conjugated to a tracer (usually a chemiluminescent or electrochemiluminescent tracer) ( ¹² ). Despite their practicality, these assays have some limitations, including different specificity of the assay’s ligand for 25(OH)D₂ and 25(OH)D₃ and cross-reactivity with vitamin D metabolites [mainly 24,25(OH)₂D] ( ¹⁶ , ¹⁷ ). Additionally, for accurate measurement of its total concentration, 25(OH)D must be completely dissociated from its binding proteins prior to the analysis, which may not occur in some situations, particularly in individuals with increased DBP (women who are pregnant or using estrogens) ( ¹⁸ ). All these factors represent potential sources of error in 25(OH)D measurement.

Liquid chromatography, coupled with tandem mass spectrometry (LC-MS/MS), is considered the gold standard for 25(OH)D measurement due to its high precision and specificity and low analytical interference ( ¹² - ¹⁴ ). Two methods developed either by the National Institute of Standards and Technology (NIST, USA) or by Ghent University (Belgium) are considered as references by the Joint Commission for Traceability in Laboratory Medicine ( ¹⁶ , ¹⁹ ). Limitations to the widespread use of LC-MS/MS in laboratories include the high cost of acquiring and maintaining the equipment, the need for specialized professionals to develop and validate the method, and less automation, requiring more labor and time for each measurement. Several LC-MS/MS assays are also prone to C3-epimer interference, which could result in falsely increased 25(OH)D levels. This occurs mainly in children under the age of 1 year, in whom C3-epimer levels are higher ( ¹² - ¹⁴ , ¹⁶ ).

Despite advances in technological developments and methodological standardizations in recent years, there are still considerable variations in 25(OH)D levels obtained in different trials, which may impact the clinical interpretation of the results ( ²⁰ ). In laboratory practice, up to 20% of variation may occur between different methods due to several factors: analytical inaccuracy and imprecision; matrix effect mainly caused by lipemia and variable DBP levels in the sample; variable and incomplete DBP-25(OH)D dissociation, especially in samples with high DBP levels; different reactivity of the assay ligand for 25(OH)D₂ and 25(OH)D₃; and cross-reactions, mainly with the C3-epimer and 24,25(OH)₂D ( ²⁰ - ²⁴ ).

The main challenge for the diagnostic market is to achieve better standardization across ongoing trials, which would provide a better comparison of results obtained in different laboratories and clinical studies. This would allow us to determine with greater certainty which individuals actually have vitamin D deficiency and to establish toxic levels with negative health impacts. Some programs, such as the Vitamin D Standardization Program (USA) and the Vitamin D External Quality Assessment Scheme (DEQAS, UK), directly target this standardization in an attempt to reduce the differences between methods ( ¹⁵ , ¹⁹ ). From a methodological standpoint and considering the current analytical variation between different methods, researchers like Binkley and Carter – both responsible for the most important proficiency testing survey currently available (DEQAS) and for the publication of several studies comparing different 25(OH)D assays – have suggested that 25(OH)D levels should be maintained between 30-40 ng/mL to ensure concentrations greater than 20-30 ng/mL, since no toxic effects occur at these levels and the real 25(OH)D concentration in the samples is generally unknown ( ¹⁹ ).

Some studies have recently suggested that measurements of the free or bioavailable 25(OH)D fraction correlate better with bone parameters than total 25(OH)D measurements, especially in some subgroups like postmenopausal women and patients with osteoporosis, chronic kidney disease on dialysis, or cirrhosis ( ²⁵ , ²⁶ ). These fractions can be estimated using Vermeulen’s formula from the values of total 25(OH)D, DBP, and albumin and their affinity constants. However, this formula is not widely accepted because it has not been validated against a reference method and is subject to the limitations of the total 25(OH)D and DBP assays used in the calculation. Depending on the type of antibody used (monoclonal versus polyclonal), DBP immunoassays may not recognize all circulating DBP isoforms, resulting in lower values of this protein and overestimating the free and bioavailable fractions. In studies comparing DBP levels in African Americans and Caucasian Americans, DBP measured by monoclonal immunoassay was lower in African Americans, whereas in other studies in which DBP was measured by polyclonal immunoassay or LC-MS/MS, this difference was not found ( ²⁷ , ²⁸ ). Other methods that allow direct measurement of the free 25(OH)D fraction include equilibrium dialysis, ultrafiltration, and some commercial immunoassays; however, none of these methods has been widely validated. Thus, these measurements are rarely available in clinical laboratories in general and, at present, have very limited indications in clinical practice.

Measurement of 1,25(OH)₂D, the active metabolite of vitamin D, is generally not recommended in the assessment of the nutritional status of vitamin D due to its short half-life (4-6 hours) and a rigid control of its serum levels by calcium, phosphorus, PTH, and FGF-23 ( ¹² , ¹³ ). Normal or even elevated levels of 1,25(OH)₂D are often found in individuals with vitamin D deficiency due to associated secondary hyperparathyroidism, with consequent increased expression of the enzyme 1α-hydroxylase (CYP27B1) and increased production of 1,25(OH)₂D. In contrast, the activity of the enzyme 25-hydroxylase (CYP2R1) is fundamentally dependent on the availability of its substrate (vitamin D) and is not influenced by its product [25(OH)D]. Because of this, 25(OH)D is a more reliable indicator of vitamin D stored in the body. In addition, since the circulating levels of 1,25(OH)₂D are 1,000 times lower than those of 25(OH)D, measurement of 1,25(OH)₂D is much more complex, and no method or reference material is currently available for that. Assays used for such measurement include radioimmunoassay with sample extraction and/or chromatography, some recently implemented automated immunoassays, and LC-MS/MS ( ¹² , ¹³ ). Measurement of 1,25(OH)₂D is only useful in some specific situations, including chronic renal failure, oncogenic osteomalacia, hereditary forms of rickets (hypophosphatemic, vitamin D resistant or associated with 1α-hydroxylase deficiency), and granulomatous diseases (sarcoidosis and some types of lymphoma).

CLINICAL CONDITIONS AT INCREASED RISK FOR VITAMIN D DEFICIENCY

The metabolite 25(OH)D is not the active form of vitamin D but is universally accepted as the main marker of vitamin D status ( ³ ). Due to growing availability of information about the consequences of vitamin D deficiency and high rates of this condition, there has been an increasing number of requests for the assessment of vitamin D status, many of which are questionable.

Plasma 25(OH)D measurement is recommended in groups with conditions at risk for vitamin D deficiency, listed in Table 1 . These clinical conditions can be grouped according to the pathophysiology of the vitamin deficiency as (A) reduced production by insufficient skin synthesis or inadequate hepatic and renal transformation, (B) increased degradation or consumption, (C) malabsorption and/or intestinal loss.

Table 1
Main clinical conditions associated with vitamin D deficiency

Insufficient production: cutaneous, hepatic, or renal	Increased metabolization/consumption	Reduced intestinal absorption
Older age	Medications: anticonvulsant agents (phenobarbital, carbamazepine, diphenylhydantoin), ketoconazole isoniazid antiretrovirals (efavirenz, tenofovir) antibiotics	Intestinal malabsorption: inflammatory diseases, celiac disease, Crohn’s disease, cystic fibrosis, pancreatic insufficiency
Dark skin	Inflammatory conditions (SLE, RA, tuberculosis)	Bariatric surgery, pancreatic or intestinal resections
Physical barriers (sunscreen, clothing, glass)	Primary hyperparathyroidism	Medications: orlistat, cholestyramine
Obesity	Osteoporosis treatment with teriparatide or PTH (1-84)
Reduced solar exposure (pregnancy, risk of skin cancer, post-transplantation, SLE)
Reduced 25(OH)D production: severe hepatic impairment
Reduced 1,25(OH)2D production/action: chronic kidney disease and vitamin D-dependent rickets type I and II, X-linked hypophosphatemic rickets, and other conditions associated with excessive FGF-23

• SLE: systemic lupus erythematosus; RA: rheumatoid arthritis; 25(OH)D: 25-hydroxyvitamin D; 1,25(OH)₂D: 1,25 dihydroxyvitamin D; FGF-23: fibroblast growth factor 23.

1. (A) Insufficient production of vitamin D occurs in the elderly (skin aging) ( ²⁹ , ³⁰ ), in individuals with dark skin, due to physical barriers (religious clothing, sunscreen, glass), in individuals who are bedridden or restricted to closed environments (neurological, psychiatric, or institutionalized patients), in obesity (mixed causes), and in pregnancy ( ³¹ - ³⁴ ). The occurrence of 25-hydroxylation of vitamin D in the liver may be compromised in states of severe hepatic impairment. In renal insufficiency, vitamin D-dependent rickets type I, and conditions with excessive FGF-23, the production of 1,25(OH)₂D is reduced due to impaired 1-alpha-hydroxylase activity, in which, low 25(OH)D concentrations may further compromise bone metabolism ( ³⁵ ).

2. (B) Increased degradation of vitamin D and its metabolites may be caused by medications that activate hepatic lysosomal enzymes, like anticonvulsant agents (carbamazepine, phenobarbital, hydantoin), antiretrovirals (efavirenz, tenofovir), antibiotics, and antifungal agents (isoniazid, ketoconazole) ( ³⁶ , ³⁷ ). Increased degradation of the vitamin may also occur due to increased consumption of 1,25(OH)₂D by inflammatory cells [as in rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), and tuberculosis]. Furthermore, low 25(OH)D may occur from increased 25(OH)D to 1,25(OH)₂D conversion by increased PTH in primary hyperparathyroidism and during treatment with PTH (teriparatide) ( ³⁸ - ⁴² ); this can occur due to increased activity of renal 1-alpha-hydroxylase ( ⁴³ ), the enzyme responsible for this conversion. On the other hand, increased 1,25(OH)₂D can induce CYP24A1 activity, which converts 25(OH)D into its inactive form, 24,25(OH)₂D. Still, other factors may also contribute to low 25(OH)D levels in hyperparathyroidism ( ⁴⁴ ).

3. (C) Intestinal malabsorption causes vitamin D to be eliminated in the feces along with fat, since vitamin D is part of the enterohepatic cycle. This occurs in disorders with intestinal inflammation or malabsorption, like celiac disease, cystic fibrosis, Crohn’s disease, and pancreatic insufficiency. It may also occur with medications that limit the absorption of vitamin D, such as cholestyramine and orlistat, and conditions with iatrogenic malabsorption following bariatric surgery and pancreatic or intestinal resections ( ¹ , ⁴⁵ ).

WHICH CONDITIONS COULD BENEFIT FROM 25(OH)D CONCENTRATIONS ABOVE 30 NG/ML?

According to the Institute of Medicine, 25(OH)D concentrations below 20 ng/mL in the general population are considered low ( ⁴ ). In contrast, evidence suggests that 25(OH)D concentrations maintained above 30 ng/mL in some clinical situations are beneficial to the patient, especially in reducing the risk of fractures. The main clinical conditions benefiting from 25(OH)D levels > 30 ng/mL are described below ( Table 2 ).

Table 2
Clinical conditions and groups that benefit from 25-hydroxyvitamin (25[OH]D) concentrations above 30 ng/mL

Groups	Clinical Conditions
Elderly (> 65 years) Pregnant women	Osteoporosis (primary or secondary) Fractures due to fragility
	Metabolic bone diseases (osteomalacia, osteogenesis imperfecta, primary hyperparathyroidism) Secondary hyperparathyroidism
	Sarcopenia Recurring falls Chronic renal disease
	Malabsorption syndrome
	Liver failure
	Anorexia nervosa
	Cancer

Elderly and falls

Due to lifestyle habits, polypharmacy, multiple comorbidities, and reduced efficacy of skin production of vitamin D, elderly individuals comprise one of the most important groups at risk of vitamin D deficiency and consequent secondary hyperparathyroidism ( ²⁹ - ³¹ ). Low 25(OH)D concentrations are associated with increased risk of fractures and falls, especially in frail and institutionalized elderly ( ⁴⁶ ). Since secondary hyperparathyroidism is very frequent in the elderly population and has harmful consequences (especially for bone mass), 25(OH)D concentrations above 30 ng/mL have been recommended for normalization of PTH levels in this population ( ³² ). This finding was similar to results from Brazilian studies, which found a threshold of around 30-32 ng/mL for 25(OH)D; levels lower than these were associated with increased serum PTH levels ( ⁴⁷ , ⁴⁸ ). However, a study evaluating 488 elderly Caucasian women was unable to find a correlation between 25(OH)D and PTH and, therefore, to define a threshold value for 25(OH)D in this population ( ⁴⁹ ).

A pooled analysis concluded that vitamin D supplementation at doses ≥ 800 IU/day was associated with a reduced risk of vertebral and femoral fractures in individuals aged ≥ 65 years ( ⁵⁰ ). The authors also observed that patients older than 85 years and those with lower 25(OH)D levels were the ones benefiting most from vitamin D supplementation. Another recent meta-analysis ( ⁵¹ ) was unable to confirm these findings but received negative criticism regarding its methodology, including the selection of the studies and lack of adjustments in terms of the evaluation of adherence to the interventions ( ⁵² ).

Elderly individuals have an increased prevalence of sarcopenia and, thus, a higher risk of falls and fractures. Presence of the vitamin D receptor (VDR) has been demonstrated in skeletal muscle precursor cells, while the number of VDRs in muscle appears to decline with aging ( ⁵³ ). A study evaluating muscle fibers after treatment with vitamin D₃ 4,000 IU in 21 elderly women with a baseline level of 25(OH)D of 18 ng/mL demonstrated increased intramyonuclear VDRs in type II muscle fibers compared with a placebo group. In addition, a 30% increase in the cross-sectional area was observed in muscle fibers along with intramyonuclear VDR concentration after treatment with vitamin D₃ ( ⁵⁴ , ⁵⁵ ). A similar finding occurs with aging and suggests that elderly individuals with low vitamin D levels may have exacerbated muscle atrophy ( ⁵⁶ ). A multicenter Italian study evaluating 401 elderly women (mean age 66.9 years) demonstrated that those with vitamin D deficiency had a significant reduction in appendicular muscle strength and physical performance compared with women with 25(OH)D levels above 30 ng/mL ( ⁵⁷ ), reinforcing the occurrence of a deleterious effect of vitamin D deficiency on the muscle ( ⁵⁸ ).

A Brazilian study has shown significant increases of 16.4% and 24.6% in the strength of hip flexors and knee extensors, respectively, after 6 months of cholecalciferol supplementation in elderly patients without any regular physical activity ( ⁵⁹ ).

Regarding vitamin D supplementation, a systematic review by Beaudart and cols. concluded that it was associated with a significant increase in overall muscle strength, more evident in individuals > 65 years and in those with very low (< 12 ng/mL) initial 25(OH)D values ( ⁶⁰ ). Similarly, a recent randomized clinical trial demonstrated that administration of vitamin D for 6 months, which resulted in a mean 25(OH)D level of 47 ng/mL, had a positive effect on increasing muscle mass and physical strength, an effect that was independent of physical activity ( ⁶¹ ).

These studies emphasize the fact that elderly individuals have, in addition to a higher risk of hypovitaminosis D, important clinical consequences, such as increased risk of falls and bone fragility, which increase the risk of fractures. According to a Cochrane review, vitamin D supplementation reduces the risk of falls in institutionalized individuals – mostly in vitamin D deficient ones – but has little effect on the risk of falls among outpatients ( ⁶² ). In contrast, a study with high doses of vitamin D, which resulted in increased 25(OH)D levels, showed the opposite effect, i.e. , an increased risk of falls in elderly individuals ( ⁶³ ). These results confirm that the administration of vitamin D at higher doses (as “bolus doses”) has no skeletal benefits, whereas daily or weekly doses are more physiological and are thus recommended.

Recently, the Vitamin D Assessment (ViDA) study, with more than 5,000 adults, demonstrated no effect of a high monthly vitamin D dose on falls ( ⁶⁴ ). Most participants had adequate 25(OH)D values prior to the intervention, which may have influenced the results.

A Brazilian study by Cangussu and cols. demonstrated an effect of vitamin D supplementation, in which an increase of 25(OH)D levels to 27.5 ± 10.4 ng/mL was associated with a reduction in the number of falls and improvement of postural balance in a group of postmenopausal women compared with a placebo group with 25(OH)D levels of 13.8 ± 6.0 ng/mL ( ⁶⁵ ). In this same group of patients, the authors had previously demonstrated a positive effect of vitamin D supplementation [and therefore increased serum 25(OH)D levels] on increasing lower limb muscle strength by 25.3% compared with the placebo group, which presented a considerable loss in this parameter, suggesting a role of vitamin D in preventing sarcopenia ( ⁶⁶ ). In a recent review, Bouillon and cols. concluded that daily supplementation with modest doses of vitamin D in elderly subjects with vitamin D deficiency may modestly improve muscle function and balance and decrease the risk of falls ( ⁶⁷ ).

In summary, vitamin D supplementation can have beneficial effects, deleterious effects, or no effect at all on the risk of falls, depending on the baseline 25(OH)D levels and the dose of vitamin D.

Pregnancy

Vitamin D deficiency is highly prevalent during pregnancy ( ⁶⁸ , ⁶⁹ ) and occurs more frequently in the first trimester. Serum 25(OH)D levels measured at the end of pregnancy, compared with levels measured early in pregnancy, correlate better with clinical outcomes, especially with increased risk of preterm delivery ( ⁷⁰ ). Vitamin D supplementation leading to serum 25(OH)D concentrations ≥ 30 ng/mL has demonstrated positive effects on genes related to preeclampsia ( ⁷¹ , ⁷² ). In a randomized controlled trial, correction of low vitamin D levels to mean concentrations of approximately 30 ng/mL significantly reduced the risk of preeclampsia and intrauterine growth retardation ( ⁷³ ). A similar finding was demonstrated in a recent Brazilian study ( ⁷⁴ ). In contrast, other studies have not demonstrated benefits from vitamin D supplementation on the risk of preeclampsia or hypertension in pregnancy ( ⁷¹ ).

Levels of 25(OH)D have also been correlated with prematurity. The risk of prematurity has been shown to be 3.8 times higher in pregnant women with serum 25(OH)D levels below 20 ng/mL compared with those with levels above 40 ng/mL ( ⁷⁰ , ⁷⁵ ).

Studies analyzing the association between 25(OH)D concentrations and birth weight have suggested a negative correlation between the vitamin concentrations and low birth weight ( ⁷⁰ , ⁷² ). A recent meta-analysis of 54 studies has shown that offspring of mothers with 25(OH)D < 55 nmol/L (22 ng/mL) are at increased risk of low birth weight and anthropometric abnormalities ( ³³ ). The study also showed an increased risk of preterm birth among mothers with 25(OH)D < 30 nmol/L (12 ng/mL) and lower scores in mental and language developmental tests among offspring of vitamin D insufficient mothers. Levels of 25(OH)D values above 75 nmol/L (30 ng/mL) showed no correlation with these abnormalities ( ³³ ). A randomized clinical trial with vitamin D deficient expectant mothers compared the supplementation with three doses of vitamin D versus placebo during and after delivery found no difference in anthropometric measures or morbidity between groups ( ⁷⁶ ).

More recently, an update of a systematic review including 30 trials (7,033 pregnant women) concluded that the supplementation with vitamin D alone during pregnancy probably reduces the risk of preeclampsia, gestational diabetes, and low birth weight (with moderate-certainty evidence) compared with placebo or no intervention. The study also showed with low-certainty evidence that vitamin D supplementation has no effect in the risk of preterm birth compared with no intervention or placebo, and may reduce the risk of severe postpartum hemorrhage ( ⁷⁷ ). Although the supplementation of vitamin D during pregnancy is still controversial, none of these studies showed major adverse effects associated with this approach.

Osteoporosis and other bone diseases

Vitamin D plays a major role in calcium absorption and bone mineralization. Low 25(OH)D levels are associated with poorer bone quality and higher fracture risk ( ⁷⁸ ). The combined effects of insufficient daily calcium intake and vitamin D deficiency lead to low bone mineral density (BMD) and increased prevalence of osteopenia and osteoporosis in Korean women ( ⁷⁸ ). Despite conflicting evidence ( ⁷⁹ ), some studies have found a significant increase in bone density and a decrease in hip and non-vertebral fractures with vitamin D supplementation alone or in combination with calcium ( ⁸⁰ , ⁸¹ ). In fact, a meta-analysis supports the use of daily vitamin D to reduce the incidence of osteoporotic non-vertebral, non-hip fractures in elderly women ( ⁸⁰ ). Vitamin D with calcium appears to achieve benefits above those attained with calcium supplementation alone for non-vertebral and non-vertebral, non-hip fractures ( ⁸⁰ ). These protective effects were more pronounced in patients with low baseline 25(OH)D levels (< 10-12 ng/mL) and in a nursing home population ( ⁸² ). Recently, a substudy from the ViDA trial including subjects with a baseline 25(OH)D level of 12 ng/mL found that monthly doses of vitamin D₃ of 100,000 IU for 2 years significantly attenuated the BMD loss at the femoral neck and total hip ( ⁸³ ).

Primary hyperparathyroidism is associated with reduced BMD and greater fracture risk. Low vitamin D levels are frequent in patients with this condition ( ⁸⁴ ), and evidence suggests that vitamin D deficiency in these patients is associated with more aggressive disease, greater levels of PTH and bone turnover markers, and a higher risk of hungry bone syndrome following parathyroidectomy ( ⁸⁵ ). Indeed, a randomized controlled trial in patients with primary hyperparathyroidism showed that vitamin D supplementation for 6 months increased the mean serum concentration of 25(OH)D from 20 ng/mL to 38 ng/mL, which resulted in improvements in lumbar spine BMD and reductions in serum C-terminal telopeptide (CTX) concentrations, without increasing serum or urinary calcium ( ⁸⁴ ). Thus, guidelines recommend serum levels of 25(OH)D to be maintained > 30 ng/mL in this group of patients ( ⁸⁶ ).

Chronic hypovitaminosis D (due to insufficient vitamin D intake or sun exposure) and/or low calcium intake can induce poor bone mineralization, leading to rickets and osteomalacia. A global consensus recommends vitamin D supplementation (400 IU) to prevent nutritional rickets and osteomalacia during childhood. Serum 25(OH)D levels above 20 ng/mL seem adequate for bone mineralization in children ( ⁸⁷ ).

Secondary hyperparathyroidism

Vitamin D and PTH are two closely interrelated metabolites, and their plasma concentrations should be interpreted in combination ( ⁸⁸ ). Vitamin D is an important inhibitor of PTH synthesis in the parathyroid and its deficiency is associated with elevated blood PTH concentrations, defined as secondary hyperparathyroidism. Increased PTH concentrations are associated with undesirable outcomes, especially in elderly populations, such as falls, fractures, and increased mortality ( ⁸⁹ , ⁹⁰ ). A prospective study in older men demonstrated that higher PTH levels were associated with an increased rate of BMD loss compared with lower PTH levels, independently of vitamin D level and renal function ( ⁹¹ ). A study evaluating femoral tomography in postmenopausal women has shown a relationship between PTH increase and cortical porosity and an increased risk of fractures ( ⁹⁰ ). The relationship between vitamin D and PTH is not linear, and the threshold at which PTH begins to rise varies widely in the literature due to the use of different assays, age groups, and calcium intake in the study populations. In general, 25(OH)D concentrations are recommended to be maintained between 20 ng/mL and 40 ng/mL to prevent the development of hyperparathyroidism secondary to vitamin D deficiency. Vitamin D deficiency should be one of the first causes to be excluded in case of doubt between a diagnosis of normocalcemic primary hyperparathyroidism and secondary hyperparathyroidism. In this scenario, 25(OH)D concentrations should be maintained above 30 ng/mL prior to investigating a suspected primary normocalcemic hyperparathyroidism ( ⁹² ). In fact, guidelines from the Fourth International Workshop on Asymptomatic Primary Hyperparathyroidism have established a serum 25(OH)D level greater than 30 ng/mL as desirable for the diagnosis of normocalcemic primary hyperparathyroidism ( ⁹³ ). A study has shown that an increase in 25(OH)D levels to 30 ng/mL with vitamin D supplementation in deficient women (< 20 ng/mL) is associated with a significant decrease in PTH levels, including in two participants in whom the baseline 25(OH)D levels were around 19 ng/mL (which could have been 20 ng/mL, considering the precision error of the method). These data showed a not well understood individual variation on the relationship between PTH and vitamin D, and indicated that some individuals may benefit from higher 25(OH)D levels and should not be overlooked ( ⁹⁴ ).

In a study with a cohort representative of the Brazilian population, the 25(OH)D threshold for PTH elevation was below 30 ng/mL, and this correlation was most evident in elderly individuals (> 65 years) ( ⁹⁵ ). Similarly, another cross-sectional study evaluating more than 300,000 paired serum PTH and 25(OH)D measurements detected a clear inverse correlation between both but found no threshold or inflection point in the curve. Levels of PTH continue to decrease as those of 25(OH)D rise and, in the study, the differences in PTH levels categorized by age range became clear. Younger individuals (< 20 years of age) have lower PTH concentrations that begin to rise when 25(OH)D concentrations are lower than 20 ng/mL. In contrast, as the prevalence of secondary hyperparathyroidism increases with age, the relationship between PTH levels and lower 25(OH)D levels becomes clearer in older individuals ( ⁹⁶ ).

Other causes of secondary hyperparathyroidism that may be indirectly related to vitamin D deficiency are those leading to intestinal malabsorption such as celiac disease, cystic fibrosis, inflammatory bowel diseases, and bariatric surgery ( ⁹⁷ ).

Bariatric surgery is a frequent cause of secondary hyperparathyroidism in which PTH concentrations can reach extreme levels caused by severe vitamin D deficiency combined with low intake and bioavailability of dietary and supplemental calcium. In the long term, these changes are associated with an increased risk of fractures ( ⁹⁸ ). Most available literature considers the target 25(OH)D level of 30 ng/mL after bariatric surgery. Doses of vitamin D above those usually recommended may be required to adjust the 25(OH)D concentrations after bariatric surgery, which should always be accompanied by adequate calcium intake ( ⁹⁸ , ⁹⁹ ). Strategies for vitamin D supplementation vary broadly in the literature. Doses below 800 IU/day seem to be insufficient to reach the target 25(OH)D blood level. Many studies suggest the administration of 50,000 IU weekly plus a daily dose, but no consensus has been reached in this regard. The ideal strategy to date is to find the best treatment regimen for each patient by titrating the dose of vitamin D until optimal plasma concentrations are reached.

However, secondary hyperparathyroidism after bariatric surgery cannot be attributed to vitamin D deficiency alone. Impaired calcium absorption seems to be a very important issue hindering improvements in secondary hyperparathyroidism, even under normal 25(OH)D concentrations (> 30 ng/mL), as described by Tardio and cols. ( ³⁴ ).

Obese individuals have lower vitamin D levels than nonobese ones, and this deficiency should be identified and corrected before bariatric surgery. The 25(OH)D levels in these patients are recommended to be maintained above 30 ng/mL before this type of surgery ( ¹⁰⁰ , ¹⁰¹ ), and depending on the surgical technique, doses much higher than conventional ones may be required after surgery to meet this goal. These concentrations should be periodically evaluated, and the doses should be titrated according to blood 25(OH)D levels ( ⁹⁹ ).

Diabetes mellitus

Several studies have addressed the supplementation of vitamin D in patients with prediabetes and diabetes, showing controversies results, especially in patients with type 2 diabetes (T2DM). Recently, Pittas et al. randomized 2,423 individuals to receive vitamin D 4,000 IU or placebo, and after 2.5 years, the authors observed no reduction in the risk of T2DM with vitamin D supplementation ( ¹⁰² ). In contrast, vitamin D supplementation may have benefits on B cell function and in the immune system in type 1 diabetes, as demonstrated in a Brazilian study ( ¹⁰³ ).

Chronic renal disease

Vitamin D deficiency is prevalent among patients with chronic renal disease (CKD) treated conservatively or with dialysis, and among kidney-transplanted patients ( ¹⁰⁴ , ¹⁰⁵ ). A meta-analysis with more than 17,000 patients concluded that hypovitaminosis D was associated with an increased risk of all-cause mortality, especially in patients undergoing dialysis. Additionally, a 10 ng/mL increase in serum 25(OH)D levels was associated with a 21% mortality reduction, while values above 25 ng/mL were associated with lower mortality risk. Of note, no additional benefit was observed in patients with 25(OH)D values greater than 35 ng/mL ( ¹⁰⁶ ).

The Kidney Disease Improving Global Outcomes (KDIGO) guidelines recommend measurement of 25(OH)D levels in patients with CKD and suggest that the ideal serum levels are similar to those recommended for the general population ( ¹⁰⁵ ). Since CKD is a chronic disease associated with increased risk of fractures, 25(OH)D concentrations above 30 ng/mL would be recommended. A randomized, double-blind, placebo-controlled study evaluated the supplementation with high doses of cholecalciferol in 120 patients with stage 3-4 CKD ( ¹⁰⁷ ). After 16 weeks, 25(OH)D serum levels were around 40 ng/mL in the treated group, which led to a significant reduction in PTH, CTX, and bone alkaline phosphatase compared with the placebo group. Even though serum 25(OH)D levels above 40 ng/mL were related to reduced bone remodeling, there was no evaluation of fracture risk. To date, no studies in this specific population have demonstrated a relationship between reduced bone remodeling and reduced risk of fragility fractures.

Cancer

ln vitro studies have indicated that 1,25(OH)₂D, the active form of vitamin D, has several antineoplastic effects, including antiproliferative and anti-inflammatory actions, inhibition of angiogenesis and metastasis, as well as stimulation of differentiation and apoptosis of malignant cells ( ¹⁰⁸ ). Accordingly, clinical observational studies have demonstrated associations between low serum 25(OH)D concentrations at baseline and increased risk of incident malignant diseases and/or mortality from cancer ( ¹⁰⁹ - ¹¹² ). Specifically, 25(OH)D serum levels lower than 25 ng/mL have been associated with a greater risk of cancer death, including digestive, central nervous, pulmonary, hematological, and breast cancers ( ¹¹⁰ ).

In another prospective study, serum 25(OH)D concentrations greater than 38 ng/mL were associated with lower rates of incident breast cancer in women with increased risk of developing this malignancy ( ¹¹¹ ). In contrast, several meta-analyses of observational studies have shown that vitamin D supplementation does not reduce the risk of incident cancers, but may decrease cancer mortality. Nevertheless, these data fail to support the hypothesis that an increase in 25(OH)D serum levels through vitamin D supplementation could reduce the incidence of cancer or improve cancer outcomes. Evidence from randomized controlled trials (RCTs) is needed to support results from observational studies. To this end, several RCTs have examined the effect of calcium and vitamin D supplementation on cancer incidence and mortality. The results, described below, are still controversial. More recently, a secondary analysis of data from the Women’s Health Initiative Calcium/Vitamin D trial showed a protective effect of calcium plus a daily dose of 400 IU of vitamin D (CaD) supplementation on the risk of hematologic malignancy ( ¹¹³ ). The mean 25(OH)D level increased from 20.1 ng/mL to 24.3 ng/mL in the CaD group and decreased from 20.8 ng/mL to 18.2 ng/mL in the placebo group. Patients in the intervention arm had a 20% decreased risk of incident hematologic malignancies [hazard ratio (HR), 0.80; 95% confidence interval (CI), 0.65-0.99], and a 54% reduction in mortality from lymphoid malignancies (HR, 0.46; 95% CI, 0.24-0.89).

In contrast, recent RCTs failed to show a reduction in the risk of incident cancer with vitamin D supplementation ( ¹¹⁴ , ¹¹⁵ ). Lappe and cols. randomized 2,303 healthy postmenopausal women aged ≥ 55 years from 31 rural counties to receive vitamin D 2,000 IU plus calcium 1,500 mg/day or placebo. The participants were allowed to take up to 800 IU per day of vitamin D supplementation, outside the intervention. The mean 25(OH)D concentration increased from 32.8 ng/mL at baseline to 43.9 ng/mL at 1 year in the active treatment group and remained unchanged in the placebo group. Over the 4-year study period, a new diagnosis of cancer was confirmed in 3.9% of patients in the vitamin D plus calcium group compared with 5.6% in the placebo group, a nonsignificant difference (p = 0.06) ( ¹¹⁴ ). Similarly, a post hoc analysis of the ViDA study, which was originally designed to assess the effect of vitamin D supplementation on the incidence of cardiovascular disease, examined whether high-dose vitamin D supplementation was associated with a reduction in cancer incidence and cancer mortality ( ¹¹⁵ ). In this RCT, 5,110 community-dwelling adults (mean age 66 years) received an initial 200,000 IU bolus of oral vitamin D₃, followed by monthly doses of 100,000 IU or placebo for a median of 3.3 years. The mean level of 25(OH)D, measured in a subgroup of participants, was 25.3 ng/mL at baseline and increased to up to 54 ng/mL in the vitamin D group, being consistently greater than 20 ng/mL than the mean level in the placebo group. There was no difference in cancer incidence or cancer mortality between vitamin D and placebo arms. In another small study, 417 adult patients with digestive tract cancers were randomized to receive vitamin D (2,000 IU/day) or placebo ( ¹¹⁶ ). Over a median follow up of 3.5 years, the percentage of cancer relapse or death was similar between the groups. In the subgroup of patients with baseline serum 25(OH)D levels between 20 ng/mL and 40 ng/mL, the 5-year relapse-free survival was greater in the vitamin D group (HR 0.46; 95% CI, 0.24-0.86). Finally, data from VITAL, a randomized placebo-controlled trial including more than 25,000 subjects (men and women older than 50 and 55 years, respectively), also demonstrated that vitamin D (2,000 IU per day) and omega-3 supplementation did not prevent cancer and cardiovascular diseases ( ¹¹⁷ ). Over a follow-up of 5.3 years, cancer was diagnosed in 1,617 subjects, and no difference was observed in the incidence of cancer between the vitamin D group and the placebo group. Although this large study demonstrated that supplementation with vitamin D did not reduce the incidence of invasive cancer, post hoc analyses excluding the first years of follow-up showed that the rate of death from cancer was significantly lower in patients receiving vitamin D than in those on placebo. It is important to point out that the majority of the patients had normal serum 25(OH)D levels at randomization (mean ± standard deviation 30.8 ± 10.0 ng/mL), which suggests that vitamin D requirement for cancer prevention was probably already met in most participants. In contrast, 25(OH)D levels were below 20 ng/mL in 12.7% of the participants and between 20 to 30 ng/mL in 32.2% of them.

In summary, while evidence from in vitro studies indicates that vitamin D has antineoplastic actions, clinical trials have not shown a role for vitamin D supplementation in reducing the incidence of cancer. Current guidelines have not proposed optimal serum levels of 25(OH)D or recommended the use of vitamin D supplementation to prevent cancer or reduce cancer death ( ⁵ , ¹¹⁸ ). However, cancer is a life-threatening disease, and some data support vitamin D supplementation in reducing cancer-related mortality ( ¹¹⁹ ). Thus, it seems reasonable to maintain optimal vitamin D levels in individuals with a recent diagnosis of cancer and in patients on adjuvant endocrine therapy leading to bone loss.

DRUGS THAT INTERFERE WITH VITAMIN D LEVELS

Long-term exposure to glucocorticoids is associated with an increased risk of bone loss and fractures ( ¹²⁰ , ¹²¹ ). The detrimental effect of glucocorticoids on bone occurs rapidly and can be explained by direct and indirect effects, including vitamin D deficiency due to increased 25(OH)D catabolism ( ¹²² - ¹²⁴ ). The 2017 American College of Rheumatology guideline recommends a serum concentration of 25(OH)D above 20 ng/mL in patients on glucocorticoid treatment ( ¹²⁴ ). However, greater 25(OH)D levels may be beneficial, and some experts endorse concentrations above 30 ng/mL ( ³ , ⁵ , ¹²⁵ ). Despite inconclusive data, serum levels of 25(OH)D greater than 30 ng/mL are recommended, and this approach may minimize bone loss and improve the efficacy of antiosteoporotic therapy in individuals with glucocorticoid-induced osteoporosis ( ¹²⁶ ).

Prolonged use of antiepileptic drugs (AEDs) increases the risk of fractures and has negative effects on mineral metabolism, which occur as early as 6 months of starting treatment, and appears to be, at least in part, mediated by vitamin D deficiency ( ¹²⁷ , ¹²⁸ ). Some AEDs, including phenytoin, phenobarbital, and carbamazepine, induce the cytochrome P450 (CYP3A4) system of liver enzymes, which increases the catabolism of 25(OH)D and 1,25(OH)₂D ( ¹²⁹ ). Prospective studies indicate that vitamin D supplementation may improve or maintain bone mass in AED users ( ¹³⁰ , ¹³¹ ). A randomized trial has shown that the administration of vitamin D to patients on long-term AEDs increased the mean 25(OH)D level from 13.8 ng/mL to 26.3 ng/mL and improved BMD at all skeletal sites ( ¹³¹ ). Optimal serum levels of 25(OH)D for patients on AEDs have not been established, but based on these data and considering that the 25(OH)D levels measured may be 20% lower than the actual levels, concentrations close to 30 ng/mL may be beneficial.

Combination antiretroviral therapy (cART) has a negative effect on bone metabolism ( ³⁷ , ¹³² ). Some drugs can lead to low BMD and fractures, including efavirenz, which is associated with a reduction in 25(OH)D levels, and tenofovir, which is related to secondary hyperparathyroidism. Efavirenz is a potent inducer of cytochrome P450 enzymes. Several of these enzymes are involved in vitamin D metabolism, and efavirenz may have the detrimental off-target effect of reducing available vitamin D substrate and active metabolites ( ¹³³ ). Several randomized clinical trials in patients treated with cART have evaluated the effects of vitamin D supplementation on biochemical and immune markers, as well as in serum 25(OH)D levels and BMD ( ¹³² - ¹³⁴ ). A study of 165 patients with HIV (aged 31-36 years) receiving efavirenz, tenofovir, and emtricitabine demonstrated that vitamin D supplementation increasing serum 25(OH)D levels to 55 ng/mL attenuated bone loss at the total hip observed in patients in the placebo arm, whose 25(OH)D concentration was unchanged at 25 ng/mL over the 48-week study period ( ¹³² ). In addition, vitamin D was associated with improved T-helper cells (Th naïve%) and decreased RNA viral load ( ¹³⁴ ) and total and non-high-density lipoprotein cholesterol ( ¹³⁵ ).

Other drugs that decrease 25(OH)D levels include orlistat, ketoconazole, cholestyramine, teriparatide, and PTH (1- ⁸⁴ ), and patients on chronic use of these medications should have their vitamin D status assessed ( ¹ ).

HYPERVITAMINOSIS D AND INTOXICATION

Excess vitamin D increases intestinal calcium uptake, renal tubular reabsorption and bone resorption, leading to hypercalcemia and related symptoms like nausea, vomiting, weakness, anorexia, dehydration, and acute renal failure ( ¹³⁶ ). Supplementation with very high doses of vitamin D may be harmful to elderly individuals and can potentially lead to falls and fractures ( ⁶³ ).

The cutoff values for hypervitaminosis D in both adults and children are not well established in the literature. In general, 25(OH)D values are considered high when above 90-100 ng/mL, but the risk of vitamin D intoxication, characterized by the presence of hypercalcemia, is higher when the 25(OH)D values are greater than 150 ng/mL ( ¹ ). Lower values, such as 75 ng/mL, have been correlated with mild hypercalcemia in children with rickets ( ¹³⁷ ), suggesting that the risk of vitamin D intoxication in children may happen with lower values of 25(OH)D.

The prevalence rates of vitamin D intoxication are still very low when compared with those of vitamin D deficiency. This was shown in a study evaluating 5,527 patients, which reported rates of vitamin D intoxication and deficiency as 2.7% and 59%, respectively ( ¹³⁶ ). However, several cases of vitamin D intoxication have been reported recently in the international literature, and this complication has increased by 7.8% in the last 5 years. It is important to note that most reports of vitamin D intoxication are related to the use of empirical or supraphysiological doses of cholecalciferol mainly by injection routes, as reported in a series of 16 cases in which patients used intramuscular injection of veterinary supplement containing high doses of vitamins A, D, and E ( ¹³⁸ ).

The usual dose for correction of vitamin D deficiency is 50,000 IU/week. For maintenance, the dose varies from 400 to 2,000 IU/daily, depending on the age and clinical condition of the patient. Importantly, these doses are effective and safe and have not been associated with hypervitaminosis D or acute intoxication resulting in hypercalcemia ( ¹³⁶ ).

REFERENCE VALUES

Based on the above review of the literature analyzing the impact of 25(OH)D values on clinical outcomes in specific situations, the Brazilian Society of Endocrinology and Metabolism and the Brazilian Society of Clinical Pathology recommend reference values of 25(OH)D stratified according to age and individual clinical characteristics:

25(OH) vitamin D concentrations:

Deficiency: <20 ng/mL Adequate for the general population < 65 years: between 20-60 ng/mL Ideal*: 30-60 ng/mL Risk of intoxication: >100 ng/mL

* Recommended for individuals with vulnerable conditions: elderly and frequent fallers, post-bariatric surgery, pregnant women, individuals using drugs that interfere with vitamin D metabolism, and patients with osteoporosis, secondary hyperparathyroidism, osteomalacia, type 1 diabetes mellitus, cancer, chronic kidney disease, or malabsorption.

So far, there is no evident benefit from maintaining 25(OH)D levels above 60 ng/mL in any clinical situation (including bone and extra-skeletal outcomes). Levels of 25(OH)D > 100 ng/mL are associated with a risk of intoxication, leading to hypercalcemia and its clinical consequences.

FINAL CONSIDERATIONS

This position statement updating the reference values of 25(OH)D calls attention to situations at risk for vitamin D deficiency and clinical conditions in which 25(OH)D levels below 30 ng/mL could have a negative impact on health. Measurement of 25(OH)D levels in all these cases is, evidently, recommended. It is worth mentioning that the recommendations by some international guidelines differ from ours ( ¹³⁹ - ¹⁴³ ), showing that this remains a controversial topic. The majority of these guidelines define the 25(OH)D values considered to be deficient for the general population. Our guideline offers a different approach, aimed at patients in special situations, for whom evidence shows that higher 25(OH)D concentrations may be beneficial.

Vitamin D is important for several biological functions particularly related to bone and mineral metabolism, according to solid evidence from in vitro , animal, and human studies. However, evidence has been reported of some effects of vitamin D on other systems (neuromuscular, immune) and cell differentiation (suggesting an association with cancer).

Randomized, double-blind, and placebo-controlled trials have been increasingly difficult to design, since due to ethical reasons, individuals with hypovitaminosis D should not receive placebo alone for a long period of time. Additionally, numerous warnings in the media about the magnitude of vitamin D deficiency and its consequences have largely reached lay and medical populations. Consequently, vitamin D supplementation has become more frequent, and it is increasingly difficult to find individuals with vitamin D deficiency to enroll in clinical studies.

• It is important to emphasize that the ideal 25(OH)D concentrations are still debatable, which runs counter to imprecise laboratory assays and genetic and clinical characteristics of the populations studied. Additionally, most studies measuring 25(OH)D levels have evaluated populations of elderly Caucasian women, and data on vitamin D status and consequences of vitamin D deficiency in men, other age groups, or other ethnicities are scarce.

• We suggest that the management of abnormal vitamin D levels should be based on the currently available literature and critical clinical reasoning. There is a strong consensus that 25(OH)D concentrations between 20 ng/mL and 40 ng/mL are reasonably safe. In view of conflicting results, we recommend the maintenance of concentrations above 30 ng/mL in populations with harmful consequences from vitamin D deficiency, as indicated in the literature. These measures should ensure that the patients receive the benefits of vitamin D sufficiency without the additional risk of overtreatment.

This document also highlights the actual risk of vitamin D intoxication when the supplementation exceeds the recommended doses for each clinical situation, which can have serious health consequences. Due to the absolute lack of evidence and potential risk of intoxication, we recommended 25(OH)D concentrations not to exceed 60 ng/mL in any clinical situation.

Acknowledgment

We thank Milena Braga-Basaria, MD (Voxmed Medical Communications) for critically reviewing and suggesting improvements to the manuscript.

REFERENCES

• ¹
  Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357(3): 266-81.
• ²
  Arantes HP, Kulak CA, Fernandes CE, Zerbini C, Bandeira F, Barbosa IC, et al. Correlation between 25-hydroxyvitamin D levels and latitude in Brazilian postmenopausal women: from the Arzoxifene Generations Trial. Osteoporos Int. 2013;24(10):2707-12.
• ³
  Maeda SS, Borba VZ, Camargo MB, Silva DM, Borges JL, Bandeira F, et al. Recommendations of the Brazilian Society of Endocrinology and Metabology (SBEM) for the diagnosis and treatment of hypovitaminosis D. Arq Bras Endocrinol Metabol. 2014;58(5):411-33.
• ⁴
  Rosen CJ, Gallagher JC. The 2011 IOM report on vitamin D and calcium requirements for North America: clinical implications for providers treating patients with low bone mineral density. J Clin Densitom. 2011;14(2):79-84.
• ⁵
  Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911-30.
• ⁶
  Cosman F, de Beur SJ, LeBoff MS, Lewiecki EM, Tanner B, Randall S, et al. Clinician’s Guide to Prevention and Treatment of Osteoporosis. Osteoporos Int. 2014;25(10):2359-81.
• ⁷
  Camacho PM, Petak SM, Binkley N, Clarke BL, Harris ST, Hurley DL, et al. American Association of Clinical Endocrinologists and American College of Endocrinology Clinical Practice Guidelines for the Diagnosis and Treatment of Postmenopausal Osteoporosis – 2016 – Executive Summary. Endocr Pract. 2016;22(9):1111-8.
• ⁸
  Kanis JA, Cooper C, Rizzoli R, Reginster JY; Scientific Advisory Board of the European Society for Clinical and Economic Aspects of Osteoporosis (ESCEO) and the Committees of Scientific Advisors and National Societies of the International Osteoporosis Foundation (IOF). European guidance for the diagnosis and management of osteoporosis in postmenopausal women. Osteoporos Int. 2019;30(1):3-44.
• ⁹
  Cesareo R, Attanasio R, Caputo M, Castello R, Chiodini I, Falchetti A, et al. Italian Association of Clinical Endocrinologists (AME) and Italian Chapter of the American Association of Clinical Endocrinologists (AACE) Position Statement: Clinical Management of Vitamin D Deficiency in Adults. Nutrients. 2018;10(5).
• ¹⁰
  Ferreira CE, Maeda S, Batista MC, Lazaretti-Castro M, Vasconcellos LS, Madeira M, et al. Consensus – reference ranges of vitamin D [25(OH)D] from the Brazilian medical societies. Brazilian Society of Clinical Pathology/Laboratory Medicine (SBPC/ML) and Brazilian Society of Endocrinology and Metabolism (SBEM). J Bras Patol Med Lab. 2017;53(6):377-81.
• ¹¹
  Pazirandeh S, Burns DL. Overview of vitamin D. UpToDate. 2019.
• ¹²
  Herrmann M, Farrell CL, Pusceddu I, Fabregat-Cabello N, Cavalier E. Assessment of vitamin D status – a changing landscape. Clin Chem Lab Med. 2017;55(1):3-26.
• ¹³
  Glendenning P, Inderjeeth CA. Controversy and consensus regarding vitamin D: Recent methodological changes and the risks and benefits of vitamin D supplementation. Crit Rev Clin Lab Sci. 2016;53(1):13-28.
• ¹⁴
  Atef SH. Vitamin D assays in clinical laboratory: past, present and future challenges. J Steroid Biochem Mol Biol. 2018;175:136-7.
• ¹⁵
  Carter GD, Berry J, Durazo-Arvizu R, Gunter E, Jones G, Jones J, et al. Hydroxyvitamin D assays: an historical perspective from DEQAS. J Steroid Biochem Mol Biol. 2018;177:30-5.
• ¹⁶
  Carter GD, Jones JC, Shannon J, Williams EL, Jones G, Kaufmann M, et al. 25-Hydroxyvitamin D assays: potential interference from other circulating vitamin D metabolites. J Steroid Biochem Mol Biol. 2016;164:134-8.
• ¹⁷
  Carter GD, Berry J, Durazo-Arvizu R, Gunter E, Jones G, Jones J, et al. Quality assessment of vitamin D metabolite assays used by clinical and research laboratories. J Steroid Biochem Mol Biol. 2017;173:100-4.
• ¹⁸
  Heijboer AC, Blankenstein MA, Kema IP, Buijs MM. Accuracy of 6 routine 25-hydroxyvitamin D assays: influence of vitamin D binding protein concentration. Clin Chem. 2012;58(3):543-8.
• ¹⁹
  Binkley N, Carter GD. Toward clarity in clinical vitamin D status assessment: 25(OH)D assay standardization. Endocrinol Metab Clin North Am. 2017;46(4):885-99.
• ²⁰
  Denimal D, Ducros V, Dupre T, Dousset B, Meunier C, Aho S, et al. Agreement of seven 25-hydroxy vitamin D(3) immunoassays and three high performance liquid chromatography methods with liquid chromatography tandem mass spectrometry. Clin Chem Lab Med. 2014;52(4):511-20.
• ²¹
  Wyness SP, Straseski JA. Performance characteristics of six automated 25-hydroxyvitamin D assays: mind your 3s and 2s. Clin Biochem. 2015;48(16-17):1089-96.
• ²²
  Saleh L, Mueller D, von Eckardstein A. Analytical and clinical performance of the new Fujirebio 25-OH vitamin D assay, a comparison with liquid chromatography-tandem mass spectrometry (LC-MS/MS) and three other automated assays. Clin Chem Lab Med. 2016;54(4):617-25.
• ²³
  Karvaly G, Meszaros K, Kovacs K, Patocs A, Sipak Z, Vasarhelyi B. Looking beyond linear regression and Bland-Altman plots: a comparison of the clinical performance of 25-hydroxyvitamin D tests. Clin Chem Lab Med. 2017;55(3):385-93.
• ²⁴
  Elsenberg E, Ten Boekel E, Huijgen H, Heijboer AC. Standardization of automated 25-hydroxyvitamin D assays: How successful is it? Clin Biochem. 2017;50(18):1126-30.
• ²⁵
  Bikle D, Bouillon R, Thadhani R, Schoenmakers I. Vitamin D metabolites in captivity? Should we measure free or total 25(OH)D to assess vitamin D status? J Steroid Biochem Mol Biol. 2017;173:105-16.
• ²⁶
  Bikle DD, Malmstroem S, Schwartz J. Current Controversies: Are Free Vitamin Metabolite Levels a More Accurate Assessment of Vitamin D Status than Total Levels? Endocrinol Metab Clin North Am. 2017;46(4):901-18.
• ²⁷
  Jassil NK, Sharma A, Bikle D, Wang X. Vitamin D binding protein and 25-hydroxyvitamin D levels: emerging clinical applications. Endocr Pract. 2017;23(5):605-13.
• ²⁸
  Shieh A, Aloia JF. Assessing Vitamin D Status in African Americans and the Influence of Vitamin D on Skeletal Health Parameters. Endocrinol Metab Clin North Am. 2017;46(1):135-52.
• ²⁹
  MacLaughlin J, Holick MF. Aging decreases the capacity of human skin to produce vitamin D3. J Clin Invest. 1985;76(4):1536-8.
• ³⁰
  Holick MF, Matsuoka LY, Wortsman J. Age, vitamin D, and solar ultraviolet. Lancet. 1989;2(8671):1104-5.
• ³¹
  van der Wielen RP, Lowik MR, van den Berg H, de Groot LC, Haller J, Moreiras O, et al. Serum vitamin D concentrations among elderly people in Europe. Lancet. 1995;346(8969):207-10.
• ³²
  Vieth R, Ladak Y, Walfish PG. Age-related changes in the 25-hydroxyvitamin D versus parathyroid hormone relationship suggest a different reason why older adults require more vitamin D. J Clin Endocrinol Metab. 2003;88(1):185-91.
• ³³
  Tous M, Villalobos M, Iglesias L, Fernandez-Barres S, Arija V. Vitamin D status during pregnancy and offspring outcomes: a systematic review and meta-analysis of observational studies. Eur J Clin Nutr. 2019.
• ³⁴
  Tardio V, Blais JP, Julien AS, Douville P, Lebel S, Biertho L, et al. Serum parathyroid hormone and 25-hydroxyvitamin D concentrations before and after biliopancreatic diversion. Obes Surg. 2018;28(7):1886-94.
• ³⁵
  Lang F, Leibrock C, Pandyra AA, Stournaras C, Wagner CA, Foller M. Phosphate Homeostasis, Inflammation and the Regulation of FGF-23. Kidney Blood Press Res. 2018;43(6):1742-8.
• ³⁶
  Zhou C, Assem M, Tay JC, Watkins PB, Blumberg B, Schuetz EG, et al. Steroid and xenobiotic receptor and vitamin D receptor crosstalk mediates CYP24 expression and drug-induced osteomalacia. J Clin Invest. 2006;116(6):1703-12.
• ³⁷
  Escota GV, Mondy K, Bush T, Conley L, Brooks JT, Onen N, et al. High Prevalence of Low Bone Mineral Density and Substantial Bone Loss over 4 Years Among HIV-Infected Persons in the Era of Modern Antiretroviral Therapy. AIDS Res Hum Retroviruses. 2016;32(1):59-67.
• ³⁸
  Dutta C, Kakati S, Barman B, Bora K. Vitamin D status and its relationship with systemic lupus erythematosus as a determinant and outcome of disease activity. Horm Mol Biol Clin Investig. 2019.
• ³⁹
  Borba VZ, Vieira JG, Kasamatsu T, Radominski SC, Sato EI, Lazaretti-Castro M. Vitamin D deficiency in patients with active systemic lupus erythematosus. Osteoporos Int. 2009;20(3):427-33.
• ⁴⁰
  Joo MH, Han MA, Park SM, Shin HH. Vitamin D Deficiency among Adults with History of Pulmonary Tuberculosis in Korea Based on a Nationwide Survey. Int J Environ Res Public Health. 2017;14(4).
• ⁴¹
  Bilezikian JP. Primary Hyperparathyroidism. J Clin Endocrinol Metab. 2018;103(11):3993-4004.
• ⁴²
  Kendler DL, Marin F, Zerbini CAF, Russo LA, Greenspan SL, Zikan V, et al. Effects of teriparatide and risedronate on new fractures in post-menopausal women with severe osteoporosis (VERO): a multicentre, double-blind, double-dummy, randomised controlled trial. Lancet. 2018;391(10117):230-40.
• ⁴³
  Clements MR, Davies M, Hayes ME, Hickey CD, Lumb GA, Mawer EB, et al. The role of 1,25-dihydroxyvitamin D in the mechanism of acquired vitamin D deficiency. Clin Endocrinol (Oxf). 1992;37(1):17-27.
• ⁴⁴
  Wang X, Sheng Z, Meng L, Su C, Trooskin S, Shapses SA. 25-Hydroxyvitamin D and Vitamin D Binding Protein Levels in Patients With Primary Hyperparathyroidism Before and After Parathyroidectomy. Front Endocrinol (Lausanne). 2019;10:171.
• ⁴⁵
  Rigterink T, Appleton L, Day AS. Vitamin D therapy in children with inflammatory bowel disease: a systematic review. World J Clin Pediatr. 2019;8(1):1-14.
• ⁴⁶
  Pasco JA, Henry MJ, Kotowicz MA, Sanders KM, Seeman E, Pasco JR, et al. Seasonal periodicity of serum vitamin D and parathyroid hormone, bone resorption, and fractures: the Geelong Osteoporosis Study. J Bone Miner Res. 2004;19(5):752-8.
• ⁴⁷
  Silva BC, Camargos BM, Fujii JB, Dias EP, Soares MM. [Prevalence of vitamin D deficiency and its correlation with PTH, biochemical bone turnover markers and bone mineral density, among patients from ambulatories]. Arq Bras Endocrinol Metabol. 2008;52(3):482-8.
• ⁴⁸
  Maeda SS, Kunii IS, Hayashi LF, Lazaretti-Castro M. Increases in summer serum 25-hydroxyvitamin D (25OHD) concentrations in elderly subjects in Sao Paulo, Brazil vary with age, gender and ethnicity. BMC Endocr Disord. 2010;10:12.
• ⁴⁹
  Sai AJ, Walters RW, Fang X, Gallagher JC. Relationship between vitamin D, parathyroid hormone, and bone health. J Clin Endocrinol Metab. 2011;96(3):E436-46.
• ⁵⁰
  Bischoff-Ferrari HA, Willett WC, Orav EJ, Lips P, Meunier PJ, Lyons RA, et al. A pooled analysis of vitamin D dose requirements for fracture prevention. N Engl J Med. 2012;367(1):40-9.
• ⁵¹
  Zhao JG, Zeng XT, Wang J, Liu L. Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults: A Systematic Review and Meta-analysis. JAMA. 2017;318(24):2466-82.
• ⁵²
  Bischoff-Ferrari HA, Dawson-Hughes B, Willett WC. Issues of trial selection and subgroup considerations in the recent meta-analysis of Zhao and colleagues on fracture reduction by calcium and vitamin D supplementation in community-dwelling older adults. Osteoporos Int. 2018;29(9):2151-2.
• ⁵³
  Bischoff-Ferrari HA, Borchers M, Gudat F, Durmuller U, Stahelin HB, Dick W. Vitamin D receptor expression in human muscle tissue decreases with age. J Bone Miner Res. 2004;19(2):265-9.
• ⁵⁴
  Olsson K, Saini A, Stromberg A, Alam S, Lilja M, Rullman E, et al. Evidence for Vitamin D Receptor Expression and Direct Effects of 1alpha,25(OH)2D3 in Human Skeletal Muscle Precursor Cells. Endocrinology. 2016;157(1):98-111.
• ⁵⁵
  Ceglia L, Niramitmahapanya S, da Silva Morais M, Rivas DA, Harris SS, Bischoff-Ferrari H, et al. A randomized study on the effect of vitamin D(3) supplementation on skeletal muscle morphology and vitamin D receptor concentration in older women. J Clin Endocrinol Metab. 2013;98(12):E1927-35.
• ⁵⁶
  Dawson-Hughes B. Vitamin D and muscle function. J Steroid Biochem Mol Biol. 2017;173:313-6.
• ⁵⁷
  Iolascon G, Letizia Mauro G, Fiore P, Cisari C, Benedetti MG, Panella L, et al. Can vitamin D deficiency influence muscle performance in post-menopausal women? A multicenter retrospective study. Eur J Phys Rehabil Med. 2017.
• ⁵⁸
  LeBlanc ES, Chou R. Vitamin D and falls-fitting new data with current guidelines. JAMA Intern Med. 2015;175(5):712-3.
• ⁵⁹
  Moreira-Pfrimer LD, Pedrosa MA, Teixeira L, Lazaretti-Castro M. Treatment of vitamin D deficiency increases lower limb muscle strength in institutionalized older people independently of regular physical activity: a randomized double-blind controlled trial. Ann Nutr Metab. 2009;54(4):291-300.
• ⁶⁰
  Beaudart C, Buckinx F, Rabenda V, Gillain S, Cavalier E, Slomian J, et al. The effects of vitamin D on skeletal muscle strength, muscle mass, and muscle power: a systematic review and meta-analysis of randomized controlled trials. J Clin Endocrinol Metab. 2014;99(11):4336-45.
• ⁶¹
  Aoki K, Sakuma M, Endo N. The impact of exercise and vitamin D supplementation on physical function in community-dwelling elderly individuals: A randomized trial. J Orthop Sci. 2018;23(4):682-7.
• ⁶²
  Cameron ID, Gillespie LD, Robertson MC, Murray GR, Hill KD, Cumming RG, et al. Interventions for preventing falls in older people in care facilities and hospitals. Cochrane Database Syst Rev. 2012;12:CD005465.
• ⁶³
  Bischoff-Ferrari HA, Dawson-Hughes B, Orav EJ, Staehelin HB, Meyer OW, Theiler R, et al. Monthly High-Dose Vitamin D Treatment for the Prevention of Functional Decline: A Randomized Clinical Trial. JAMA Intern Med. 2016;176(2):175-83.
• ⁶⁴
  Scragg RKR. Overview of results from the Vitamin D Assessment (ViDA) study. J Endocrinol Invest. 2019.
• ⁶⁵
  Cangussu LM, Nahas-Neto J, Orsatti CL, Poloni PF, Schmitt EB, Almeida-Filho B, et al. Effect of isolated vitamin D supplementation on the rate of falls and postural balance in postmenopausal women fallers: a randomized, double-blind, placebo-controlled trial. Menopause. 2016;23(3):267-74.
• ⁶⁶
  Cangussu LM, Nahas-Neto J, Orsatti CL, Bueloni-Dias FN, Nahas EA. Effect of vitamin D supplementation alone on muscle function in postmenopausal women: a randomized, double-blind, placebo-controlled clinical trial. Osteoporos Int. 2015;26(10):2413-21.
• ⁶⁷
  Bouillon R, Marcocci C, Carmeliet G, Bikle D, White JH, Dawson-Hughes B, et al. Skeletal and Extraskeletal Actions of Vitamin D: Current Evidence and Outstanding Questions. Endocr Rev. 2019;40(4):1109-51.
• ⁶⁸
  Amegah AK, Klevor MK, Wagner CL. Maternal vitamin D insufficiency and risk of adverse pregnancy and birth outcomes: a systematic review and meta-analysis of longitudinal studies. PLoS One. 2017;12(3):e0173605.
• ⁶⁹
  Sharma N, Nath C, Mohammad J. Vitamin D status in pregnant women visiting a tertiary care center of North Eastern India. J Family Med Prim Care. 2019;8(2):356-60.
• ⁷⁰
  Santamaria C, Bi WG, Leduc L, Tabatabaei N, Jantchou P, Luo ZC, et al. Prenatal vitamin D status and offspring’s growth, adiposity and metabolic health: a systematic review and meta-analysis. Br J Nutr. 2018;119(3):310-9.
• ⁷¹
  Mirzakhani H, Litonjua AA, McElrath TF, O’Connor G, Lee-Parritz A, Iverson R, et al. Early pregnancy vitamin D status and risk of preeclampsia. J Clin Invest. 2016;126(12):4702-15.
• ⁷²
  Wang H, Xiao Y, Zhang L, Gao Q. Maternal early pregnancy vitamin D status in relation to low birth weight and small-for-gestational-age offspring. J Steroid Biochem Mol Biol. 2018;175:146-50.
• ⁷³
  Ali AM, Alobaid A, Malhis TN, Khattab AF. Effect of vitamin D3 supplementation in pregnancy on risk of pre-eclampsia – Randomized controlled trial. Clin Nutr. 2018.
• ⁷⁴
  Pereira-Santos M, Carvalho GQ, Louro ID, Dos Santos DB, Oliveira AM. Polymorphism in the vitamin D receptor gene is associated with maternal vitamin D concentration and neonatal outcomes: A Brazilian cohort study. Am J Hum Biol. 2019;31(4):e23250.
• ⁷⁵
  Wagner CL, Baggerly C, McDonnell SL, Baggerly L, Hamilton SA, Winkler J, et al. Post-hoc comparison of vitamin D status at three timepoints during pregnancy demonstrates lower risk of preterm birth with higher vitamin D closer to delivery. J Steroid Biochem Mol Biol. 2015;148:256-60.
• ⁷⁶
  Roth DE, Gernand AD, Al Mahmud A. Vitamin D Supplementation in Pregnancy and Lactation and Infant Growth. N Engl J Med. 2018;379(19):1881.
• ⁷⁷
  Palacios C, Kostiuk LK, Pena-Rosas JP. Vitamin D supplementation for women during pregnancy. Cochrane Database Syst Rev. 2019;7:CD008873.
• ⁷⁸
  Chon SJ, Koh YK, Heo JY, Lee J, Kim MK, Yun BH, et al. Effects of vitamin D deficiency and daily calcium intake on bone mineral density and osteoporosis in Korean postmenopausal woman. Obstet Gynecol Sci. 2017;60(1):53-62.
• ⁷⁹
  Bolland MJ, Grey A, Avenell A. Effects of vitamin D supplementation on musculoskeletal health: a systematic review, meta-analysis, and trial sequential analysis. Lancet Diabetes Endocrinol. 2018;6(11):847-58.
• ⁸⁰
  Bischoff-Ferrari HA, Willett WC, Wong JB, Giovannucci E, Dietrich T, Dawson-Hughes B. Fracture prevention with vitamin D supplementation: a meta-analysis of randomized controlled trials. JAMA. 2005;293(18):2257-64.
• ⁸¹
  Jackson RD, LaCroix AZ, Gass M, Wallace RB, Robbins J, Lewis CE, et al. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006;354(7):669-83.
• ⁸²
  Tang BM, Eslick GD, Nowson C, Smith C, Bensoussan A. Use of calcium or calcium in combination with vitamin D supplementation to prevent fractures and bone loss in people aged 50 years and older: a meta-analysis. Lancet. 2007;370(9588):657-66.
• ⁸³
  Reid IR, Horne AM, Mihov B, Gamble GD, Al-Abuwsi F, Singh M, et al. Effect of monthly high-dose vitamin D on bone density in community-dwelling older adults substudy of a randomized controlled trial. J Intern Med. 2017;282(5):452-60.
• ⁸⁴
  Stein EM, Dempster DW, Udesky J, Zhou H, Bilezikian JP, Shane E, et al. Vitamin D deficiency influences histomorphometric features of bone in primary hyperparathyroidism. Bone. 2011;48(3):557-61.
• ⁸⁵
  Pallan S, Khan A. Primary hyperparathyroidism: Update on presentation, diagnosis, and management in primary care. Can Fam Physician. 2011;57(2):184-9.
• ⁸⁶
  Bilezikian JP, Brandi ML, Eastell R, Silverberg SJ, Udelsman R, Marcocci C, et al. Guidelines for the management of asymptomatic primary hyperparathyroidism: summary statement from the Fourth International Workshop. J Clin Endocrinol Metab. 2014;99(10):3561-9.
• ⁸⁷
  Munns CF, Shaw N, Kiely M, Specker BL, Thacher TD, Ozono K, et al. Global Consensus Recommendations on Prevention and Management of Nutritional Rickets. Horm Res Paediatr. 2016;85(2):83-106.
• ⁸⁸
  Autier P, Boniol M, Pizot C, Mullie P. Vitamin D status and ill health: a systematic review. Lancet Diabetes Endocrinol. 2014;2(1):76-89.
• ⁸⁹
  Domiciano DS, Machado LG, Lopes JB, Figueiredo CP, Caparbo VF, Oliveira RM, et al. Bone Mineral Density and Parathyroid Hormone as Independent Risk Factors for Mortality in Community-Dwelling Older Adults: A Population-Based Prospective Cohort Study in Brazil. The Sao Paulo Ageing & Health (SPAH) Study. J Bone Miner Res. 2016;31(6):1146-57.
• ⁹⁰
  Osima M, Borgen TT, Lukic M, Grimnes G, Joakimsen RM, Eriksen EF, et al. Serum parathyroid hormone is associated with increased cortical porosity of the inner transitional zone at the proximal femur in postmenopausal women: the Tromso Study. Osteoporos Int. 2018;29(2):421-31.
• ⁹¹
  Curtis JR, Ewing SK, Bauer DC, Cauley JA, Cawthon PM, Barrett-Connor E, et al. Association of intact parathyroid hormone levels with subsequent hip BMD loss: the Osteoporotic Fractures in Men (MrOS) Study. J Clin Endocrinol Metab. 2012;97(6):1937-44.
• ⁹²
  Cusano NE, Silverberg SJ, Bilezikian JP. Normocalcemic primary hyperparathyroidism. J Clin Densitom. 2013;16(1):33-9.
• ⁹³
  Eastell R, Brandi ML, Costa AG, D’Amour P, Shoback DM, Thakker RV. Diagnosis of asymptomatic primary hyperparathyroidism: proceedings of the Fourth International Workshop. J Clin Endocrinol Metab. 2014;99(10):3570-9.
• ⁹⁴
  Vilaça T, Camargo MB, Rocha OF, Lazaretti-Castro M. Vitamin D supplementation and strontium ranelate absorption in postmenopausal women with low bone mass. Eur J Endocrinol. 2014;170(4):469-75.
• ⁹⁵
  Maeda SS, Saraiva GL, Kunii IS, Hayashi LF, Cendoroglo MS, Ramos LR, et al. Factors affecting vitamin D status in different populations in the city of Sao Paulo, Brazil: the Sao PAulo vitamin D Evaluation Study (SPADES). BMC Endocr Disord. 2013;13:14.
• ⁹⁶
  Valcour A, Blocki F, Hawkins DM, Rao SD. Effects of age and serum 25-OH-vitamin D on serum parathyroid hormone levels. J Clin Endocrinol Metab. 2012;97(11):3989-95.
• ⁹⁷
  Santos MT, Souza FI, Fonseca FL, Lazaretti-Castro M, Sarni RO. [Changes in bone metabolism markers in women after Roux-en-Y gastric bypass]. Arq Bras Endocrinol Metabol. 2012;56(6):376-82.
• ⁹⁸
  Peterson LA. Bariatric surgery and vitamin D: key messages for surgeons and clinicians before and after bariatric surgery. Minerva Chir. 2016;71(5):322-36.
• ⁹⁹
  Borges JLC, Miranda ISM, Sarquis MMS, Borba V, Maeda SS, Lazaretti-Castro M, et al. Obesity, Bariatric Surgery, and Vitamin D. J Clin Densitom. 2017.
• ¹⁰⁰
  Plesner JL, Dahl M, Fonvig CE, Nielsen TRH, Kloppenborg JT, Pedersen O, et al. Obesity is associated with vitamin D deficiency in Danish children and adolescents. J Pediatr Endocrinol Metab. 2018;31(1):53-61.
• ¹⁰¹
  Pereira-Santos M, Costa PR, Assis AM, Santos CA, Santos DB. Obesity and vitamin D deficiency: a systematic review and meta-analysis. Obes Rev. 2015;16(4):341-9.
• ¹⁰²
  Pittas AG, Dawson-Hughes B, Sheehan P, Ware JH, Knowler WC, Aroda VR, et al. Vitamin D Supplementation and Prevention of Type 2 Diabetes. N Engl J Med. 2019;381(6):520-30.
• ¹⁰³
  Gabbay MA, Sato MN, Finazzo C, Duarte AJ, Dib SA. Effect of cholecalciferol as adjunctive therapy with insulin on protective immunologic profile and decline of residual beta-cell function in new-onset type 1 diabetes mellitus. Arch Pediatr Adolesc Med. 2012;166(7):601-7.
• ¹⁰⁴
  Vilarta CF, Unger MD, Dos Reis LM, Dominguez WV, David-Neto E, Moyses RM, et al. Hypovitaminosis D in patients undergoing kidney transplant: the importance of sunlight exposure. Clinics (Sao Paulo). 2017;72(7):415-21.
• ¹⁰⁵
  Ketteler M, Block GA, Evenepoel P, Fukagawa M, Herzog CA, McCann L, et al. Diagnosis, Evaluation, Prevention, and Treatment of Chronic Kidney Disease-Mineral and Bone Disorder: Synopsis of the Kidney Disease: Improving Global Outcomes 2017 Clinical Practice Guideline Update. Ann Intern Med. 2018.
• ¹⁰⁶
  Jayedi A, Soltani S, Shab-Bidar S. Vitamin D status and all-cause mortality in patients with chronic kidney disease: A systematic review and dose-response meta-analysis. J Clin Endocrinol Metab. 2017.
• ¹⁰⁷
  Yadav AK, Kumar V, Banerjee D, Gupta KL, Jha V. The Effect of Vitamin D Supplementation on Bone Metabolic Markers in Chronic Kidney Disease. J Bone Miner Res. 2018;33(3):404-9.
• ¹⁰⁸
  Feldman D, Krishnan AV, Swami S, Giovannucci E, Feldman BJ. The role of vitamin D in reducing cancer risk and progression. Nat Rev Cancer. 2014;14(5):342-57.
• ¹⁰⁹
  Wong G, Lim WH, Lewis J, Craig JC, Turner R, Zhu K, et al. Vitamin D and cancer mortality in elderly women. BMC Cancer. 2015;15:106.
• ¹¹⁰
  Yao S, Kwan ML, Ergas IJ, Roh JM, Cheng TD, Hong CC, et al. Association of Serum Level of Vitamin D at Diagnosis With Breast Cancer Survival: A Case-Cohort Analysis in the Pathways Study. JAMA Oncol. 2017;3(3):351-7.
• ¹¹¹
  O’Brien KM, Sandler DP, Taylor JA, Weinberg CR. Serum Vitamin D and Risk of Breast Cancer within Five Years. Environ Health Perspect. 2017;125(7):077004.
• ¹¹²
  Lee JE, Li H, Chan AT, Hollis BW, Lee IM, Stampfer MJ, et al. Circulating levels of vitamin D and colon and rectal cancer: the Physicians’ Health Study and a meta-analysis of prospective studies. Cancer Prev Res (Phila). 2011;4(5):735-43.
• ¹¹³
  Ammann EM, Drake MT, Haraldsson B, Wallace RB, Johnson KC, Desai P, et al. Incidence of hematologic malignancy and cause-specific mortality in the Women’s Health Initiative randomized controlled trial of calcium and vitamin D supplementation. Cancer. 2017;123(21):4168-77.
• ¹¹⁴
  Lappe J, Garland C, Gorham E. Vitamin D Supplementation and Cancer Risk. JAMA. 2017;318(3):299-300.
• ¹¹⁵
  Scragg R, Khaw KT, Toop L, Sluyter J, Lawes CMM, Waayer D, et al. Monthly High-Dose Vitamin D Supplementation and Cancer Risk: A Post Hoc Analysis of the Vitamin D Assessment Randomized Clinical Trial. JAMA Oncol. 2018;4(11):e182178.
• ¹¹⁶
  Urashima M, Ohdaira H, Akutsu T, Okada S, Yoshida M, Kitajima M, et al. Effect of Vitamin D Supplementation on Relapse-Free Survival Among Patients With Digestive Tract Cancers: The AMATERASU Randomized Clinical Trial. JAMA. 2019;321(14):1361-9.
• ¹¹⁷
  Manson JE, Cook NR, Lee IM, Christen W, Bassuk SS, Mora S, et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. N Engl J Med. 2019;380(1):33-44.
• ¹¹⁸
  Cianferotti L, Bertoldo F, Bischoff-Ferrari HA, Bruyere O, Cooper C, Cutolo M, et al. Vitamin D supplementation in the prevention and management of major chronic diseases not related to mineral homeostasis in adults: research for evidence and a scientific statement from the European society for clinical and economic aspects of osteoporosis and osteoarthritis (ESCEO). Endocrine. 2017;56(2):245-61.
• ¹¹⁹
  Keum N, Giovannucci E. Vitamin D supplements and cancer incidence and mortality: a meta-analysis. Br J Cancer. 2014;111(5):976-80.
• ¹²⁰
  Rossini M, Viapiana O, Vitiello M, Malavolta N, La Montagna G, Maddali Bongi S, et al. Prevalence and incidence of osteoporotic fractures in patients on long-term glucocorticoid treatment for rheumatic diseases: the Glucocorticoid Induced OsTeoporosis TOol (GIOTTO) study. Reumatismo. 2017;69(1):30-9.
• ¹²¹
  Amiche MA, Albaum JM, Tadrous M, Pechlivanoglou P, Levesque LE, Adachi JD, et al. Efficacy of osteoporosis pharmacotherapies in preventing fracture among oral glucocorticoid users: a network meta-analysis. Osteoporos Int. 2016;27(6):1989-98.
• ¹²²
  Ortego-Jurado M, Callejas-Rubio JL, Rios-Fernandez R, Gonzalez-Moreno J, Gonzalez Ramirez AR, Gonzalez-Gay MA, et al. Oral Calcidiol Is More Effective Than Cholecalciferol Supplementation to Reach Adequate 25(OH)D Levels in Patients with Autoimmune Diseases Chronically Treated with Low Doses of Glucocorticoids: A “Real-Life” Study. J Osteoporos. 2015;2015:729451.
• ¹²³
  Skversky AL, Kumar J, Abramowitz MK, Kaskel FJ, Melamed ML. Association of glucocorticoid use and low 25-hydroxyvitamin D levels: results from the National Health and Nutrition Examination Survey (NHANES): 2001-2006. J Clin Endocrinol Metab. 2011;96(12):3838-45.
• ¹²⁴
  Buckley L, Guyatt G, Fink H, McAlindon T. 2017 American College of Rheumatology Guideline for the Prevention and Treatment of Glucocorticoid-Induced Osteoporosis. Arthritis Care Res (Hoboken). 2017.
• ¹²⁵
  Mazziotti G, Formenti AM, Adler RA, Bilezikian JP, Grossman A, Sbardella E, et al. Glucocorticoid-induced osteoporosis: pathophysiological role of GH/IGF-I and PTH/VITAMIN D axes, treatment options and guidelines. Endocrine. 2016;54(3):603-11.
• ¹²⁶
  Lima GL, Paupitz JA, Aikawa NE, Alvarenga JC, Pereira RMR. A randomized double-blind placebo-controlled trial of vitamin D supplementation in juvenile-onset systemic lupus erythematosus: positive effect on trabecular microarchitecture using HR-pQCT. Osteoporos Int. 2018;29(3):587-94.
• ¹²⁷
  Jette N, Lix LM, Metge CJ, Prior HJ, McChesney J, Leslie WD. Association of antiepileptic drugs with nontraumatic fractures: a population-based analysis. Arch Neurol. 2011;68(1):107-12.
• ¹²⁸
  Nicholas JM, Ridsdale L, Richardson MP, Grieve AP, Gulliford MC. Fracture risk with use of liver enzyme inducing antiepileptic drugs in people with active epilepsy: cohort study using the general practice research database. Seizure. 2013;22(1):37-42.
• ¹²⁹
  Kulak CA, Borba VZ, Bilezikian JP, Silvado CE, Paola L, Boguszewski CL. Bone mineral density and serum levels of 25 OH vitamin D in chronic users of antiepileptic drugs. Arq Neuropsiquiatr. 2004;62(4):940-8.
• ¹³⁰
  Lazzari AA, Dussault PM, Thakore-James M, Gagnon D, Baker E, Davis SA, et al. Prevention of bone loss and vertebral fractures in patients with chronic epilepsy – antiepileptic drug and osteoporosis prevention trial. Epilepsia. 2013;54(11):1997-2004.
• ¹³¹
  Mikati MA, Dib L, Yamout B, Sawaya R, Rahi AC, Fuleihan Gel H. Two randomized vitamin D trials in ambulatory patients on anticonvulsants: impact on bone. Neurology. 2006;67(11):2005-14.
• ¹³²
  Overton ET, Chan ES, Brown TT, Tebas P, McComsey GA, Melbourne KM, et al. Vitamin D and Calcium Attenuate Bone Loss With Antiretroviral Therapy Initiation: A Randomized Trial. Ann Intern Med. 2015;162(12):815-24.
• ¹³³
  Wohl DA, Orkin C, Doroana M, Pilotto JH, Sungkanuparph S, Yeni P, et al. Change in vitamin D levels and risk of severe vitamin D deficiency over 48 weeks among HIV-1-infected, treatment-naive adults receiving rilpivirine or efavirenz in a Phase III trial (ECHO). Antivir Ther. 2014;19(2):191-200.
• ¹³⁴
  Stallings VA, Schall JI, Hediger ML, Zemel BS, Tuluc F, Dougherty KA, et al. High-dose vitamin D3 supplementation in children and young adults with HIV: a randomized, placebo-controlled trial. Pediatr Infect Dis J. 2015;34(2):e32-40.
• ¹³⁵
  Longenecker CT, Hileman CO, Carman TL, Ross AC, Seydafkan S, Brown TT, et al. Vitamin D supplementation and endothelial function in vitamin D deficient HIV-infected patients: a randomized placebo-controlled trial. Antivir Ther. 2012;17(4):613-21.
• ¹³⁶
  Sharma LK, Dutta D, Sharma N, Gadpayle AK. The increasing problem of subclinical and overt hypervitaminosis D in India: An institutional experience and review. Nutrition. 2017;34:76-81.
• ¹³⁷
  Vanstone MB, Oberfield SE, Shader L, Ardeshirpour L, Carpenter TO. Hypercalcemia in children receiving pharmacologic doses of vitamin D. Pediatrics. 2012;129(4):e1060-3.
• ¹³⁸
  De Francesco Daher E, Mesquita Martiniano LV, Lopes Lima LL, Viana Leite Filho NC, de Oliveira Souza LE, Duarte Fernandes PH, et al. Acute kidney injury due to excessive and prolonged intramuscular injection of veterinary supplements containing vitamins A, D and E: A series of 16 cases. Nefrologia. 2017;37(1):61-7.
• ¹³⁹
  Ross AC, Manson JE, Abrams SA, Aloia JF, Brannon PM, Clinton SK, et al. The 2011 report on dietary reference intakes for calcium and vitamin D from the Institute of Medicine: what clinicians need to know. J Clin Endocrinol Metab. 2011;96(1):53-8.
• ¹⁴⁰
  Scientific Advisory Committee on Nutrition (SACN). Available from: https://www.gov.uk/government/groups/scientific-advisory- committee-on-nutrition
  » https://www.gov.uk/government/groups/scientific-advisory- committee-on-nutrition
• ¹⁴¹
  Nordic Nutrition Recommendations 2012. Integrating nutrition and physical activity. Available from: https://www.norden.org/en/publication/nordic-nutrition-recommendations-2012
  » https://www.norden.org/en/publication/nordic-nutrition-recommendations-2012
• ¹⁴²
  EFSA Technical report. Outcome of a public consultation on the Draft Scientific Opinion of the EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA) on Dietary Reference Values for vitamin D 2016. Available from: https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/sp.efsa.2016.EN-1078
  » https://efsa.onlinelibrary.wiley.com/doi/epdf/10.2903/sp.efsa.2016.EN-1078
• ¹⁴³
  Health Council of the Netherlands. 2012. Evaluation of dietary reference values for vitamin D. The Hague: Health Council of the Netherlands, publication no. 2012/15E.

• erratum
  DOI: 10.20945/2359-3997000000258
  Arch Endocrinol Metab. 2020;64(4):462-78
  Where you read (TITLE):
  Reference values of 25-hydroxyvitamin D revisited: a position statement from the Brazilian Society of Endocrinology and Metabolism (SBEM) and the Brazilian Society of Clinical Pathology/Laboratory Medicine (SBPC)
  Should read:
  Reference values of 25-hydroxyvitamin D revisited: a position statement from the Brazilian Society of Endocrinology and Metabolism (SBEM) and the Brazilian Society of Clinical Pathology/Laboratory Medicine ( SBPC/ML )
  Where you read (TEXT):
  These assays include a first step in which 25(OH)D is dissociated from its carrier proteins. In a second step, the 25(OH)D in the sample competes with an analogue for the same sites of the ligand's assay [anti-25(OH)D or DBP antibodies] .
  Should read:
  These assays include a first step in which 25(OH)D is dissociated from its carrier proteins. In a second step, the 25(OH)D in the sample competes with an analogue for the same sites of the ligand's assay [anti-25(OH)D antibodies and DBP] .
  Where you read:
  Table 2
  Clinical conditions and groups that benefit from 25-hydroxyvitamin (25[OH]D) concentrations above 30 ng/mL
  

  Groups	Clinical Conditions
  Elderly (> 65 years)	Osteoporosis (primary or secondary)
  Pregnant women	Fractures due to fragility
  	Metabolic bone diseases (osteomalacia, osteogenesis imperfecta, primary hyperparathyroidism) Secondary hyperparathyroidism
  	Sarcopenia
  	Recurring falls
  	Chronic renal disease
  	Malabsorption syndrome
  	Liver failure
  	Anorexia nervosa
  	Cancer

  Should read:
  Table 2
  Clinical conditions and groups that benefit from 25-hydroxyvitamin (25[OH]D) concentrations above 30 ng/mL
  

  Groups	Clinical Conditions
  Elderly (> 65 years)	Osteoporosis (primary or secondary)
  Pregnant women	Fractures due to fragility
  	Metabolic bone diseases (osteomalacia, osteogenesis imperfecta, primary hyperparathyroidism) Secondary hyperparathyroidism
  	Sarcopenia
  	Recurring falls
  	Chronic renal disease
  	Malabsorption syndrome
  	Liver failure
  	Diabetes mellitus type 1
  	Cancer

  Where you read:
  Correspondence to:
  Carolina Moreira
  Rua Leão Júnior, 285
  80060-000 – Curitiba, PR Brasil
  [e-mail]
  Should read:
  Carolina Moreira
  Av Agostinho Leão Júnior, 285
  80060-000 – Curitiba, PR Brasil
  [e-mail]

Publication Dates

• Publication in this collection
  05 June 2020
• Date of issue
  Jul-Aug 2020

History

• Received
  2 June 2019
• Accepted
  1 Mar 2020