25-Hydroxyvitamin D as a biomarker of vitamin D status in plaque psoriasis and other dermatological diseases: a cross-sectional study

ABSTRACT BACKGROUND: Hypovitaminosis D is a public health problem associated with several chronic inflammatory and immunological diseases, including psoriasis. OBJECTIVES: This study aimed to determine the prevalence of hypovitaminosis D in patients with plaque psoriasis. A comparison was made between vitamin D levels in patients with psoriasis and those with other non-inflammatory dermatoses without photosensitivity. In addition, it evaluated the effects of the patients’ Fitzpatrick skin phototype and the season of the year on the serum levels of vitamin D. DESIGN AND SETTINGS: A retrospective cross-sectional study was conducted at an outpatient clinic in a university center in Juiz de Fora (MG), Brazil. METHODS: A review of dermatology patients’ demographic data, including skin phototype and serum levels of 25-hydroxyvitamin D [25(OH)D], over 12 months in 2016. RESULTS: This study included 554 patients: 300 patients allocated to the plaque psoriasis group and 254 control patients with other dermatological diseases. Regarding the season of the year, 229, 132, 62, and 131 participants were evaluated in summer, autumn, winter, and spring, respectively. As for the skin phototype, 397, 139, and 18 patients had phototypes III, IV, and V, respectively. The serum levels of 25(OH)D were significantly lower in the psoriasis group (24.91 ± 7.16 ng/mL) than in the control group (30.37 ± 8.14 ng/mL). CONCLUSIONS: Hypovitaminosis D (< 30 ng/mL) was present in 76.66% of patients with psoriasis versus 53.94% of control patients. Vitamin D deficiency (< 20 ng/mL) was observed in 25% of the patients with psoriasis versus 8.66% in the control group (P < 0.001). The season and patient’s skin phototype were independent predictors of serum vitamin D levels.


INTRODUCTION
Psoriasis is a chronic inflammatory disease with a genetic predisposition involving the skin, joints, and immunological effector mechanisms, affecting approximately 2-5% of the world population. The pathogenesis is multifactorial, involving innate and adaptive immunity, and potentially associated with several comorbidities. 1,2 Vitamin D is a steroid hormone that acts genomically and non-genomically in different metabolic processes in most tissues. In the skin it plays several important biological functions in the physiology of keratinocytes and cells of innate and adaptive immunity. Several studies have demonstrated a high prevalence of vitamin D deficiency in the general population and its various associations with bone, autoimmune, inflammatory, hormonal, cardiac, and neoplastic diseases. [3][4][5][6][7][8] Scientific literature suggests an association between psoriasis and inadequate levels of vitamin D. 9,10 Therefore, it is believed that the prevalence of hypovitaminosis D is higher in patients with psoriasis. Although vitamin D analogs treat psoriasis, its exact mechanism of action and relationship with the disease is unclear. 11

OBJECTIVES
The present study aimed to evaluate the serum levels of 25- 13 the following parameters were adopted: values lower than 20 ng/mL were considered deficient, values from 20 ng/mL to lower than 30 ng/mL were considered insufficient, and values equal to or above 30 ng/mL were considered sufficient.

Statistical analysis
A descriptive data analysis was performed, and the normality of

RESULTS
The demographic characteristics and parameters of the two groups are shown in Table 1. Our sample consisted of 554 patients, 300 with plaque psoriasis (54.15%) and 254 patients (45.85%) with other dermatoses. The mean age in the case group was significantly higher (47.23 ± 12.82 versus 41.59 ± 12.09 years; P < 0.001). Regarding sex distribution, 338 were women, and 216 were men. The distribution by sex showed statistically significant differences between the two groups (P < 0.001). The case group had more men (53.6%), and the control group had more women (78.4%). Serum 25(OH)D levels were significantly lower in the psoriasis group (24.91 ± 7.16 ng/mL) than in controls (30.37 ± 8.14 ng/mL), with P < 0.001 (Figure 1).
Regarding the skin phototype, there was a predominance of phototype III (397 patients, 71.   According to the American Academy of Endocrinology guidelines, 13    dietary intake, and year's season. 21 In the multivariate analysis, phototype and season of the year were the independent variables statistically significantly associated with 25(OH)D serum concentrations.

Juiz de Fora is a city in the Zona da Mata region of Minas
Gerais, located in the intertropical zone. Therefore, it receives a large amount of sunlight throughout the year, and this study was conducted in a city with a high ultraviolet index, ranging from moderate to high. Although more than 40% of the tests were performed during summer and to a lesser extent in winter (11%), a high insufficiency rate of 25(OH)D was detected.
In a review carried out by Corrêa 22  The exacerbation of psoriasis in winter may be partly due to low sun exposure and the subsequent low vitamin D production in the skin. Therefore, the therapeutic effect of UVB therapy in treating psoriasis may be, at least in part, mediated by UVB causing the synthesis of vitamin D in the skin. In addition, UVB therapy increased serum 25(OH)D levels in patients with psoriasis in parallel with disease improvement. 26  Although sunlight was the primary source of vitamin D during more than 99% of human evolution, it is clear that mainly owing to increased longevity, people need to try to accomplish a delicate balance between limiting sunlight exposure, avoiding skin damage, and optimizing vitamin D status. In many cases, this balance implies that vitamin D supplementation is necessary.
A Brazilian study conducted by Coutinho et al. 31 in 174 fishermen analyzed the relationship between sun exposure index, vitamin D levels, and clinical changes in the skin caused by the sun. Vitamin D deficiency was verified in only 11.46% of the patients due to chronic sun exposure in Brazil's northeast region, with high levels of UVI throughout the year. The lack of association between our study and that conducted by Coutinho et al. can be explained by the fact that our study showed a higher prevalence of vitamin D deficiency, as it was performed in a geographic region with a variation in sun exposure according to the season of the year, as well as the presence of atmospheric pollution in the Southeast region. On the other hand, our findings are similar to those of Cabral et al., 32

found in another
Brazilian study in the Northeast region.
To the best of our knowledge, this is the first Brazilian study to assess the prevalence of hypovitaminosis D in dermatological patients for 12 months in an expressive cohort. Therefore, the data from this study can be considered representative of a considerable proportion of dermatological patients, including patients with psoriasis in Brazil.
The limitations of our study include the absence of a dietary and sun-exposure survey (with time and duration of exposure). In addition, 25(OH)D production and degradation is a continuous process. Therefore, establishing an ideal period to study the effects of UV radiation on vitamin D production and its action on immunosuppression is a challenge in clinical research. Consequently, it needs to be better evaluated in prospective studies. In addition, as this study was cross-sectional, the patients were not followed up over a long period of restrictive selection criteria.

CONCLUSION
Considering the geographic location in which the study was carried out, with moderate to high levels of ultraviolet radiation throughout the year and the predominance of skin phototype III, it can be concluded that daily solar radiation was insufficient to promote the adequate synthesis of 25(OH)D. Furthermore, vitamin D deficiency was greater in the psoriasis group. A negative association was found among 25(OH)D, psoriasis, and phototypes IV and V, and a positive association between 25(OH)D and summer. Future randomized, blinded, long-term studies investigating the role of vitamin D supplementation in psoriasis are necessary.