No correlation was observed between vitamin D levels and disability of patients with multiple sclerosis between latitudes 18° and 30° South

Não foi observada correlação entre os níveis séricos de vitamina D e a incapacidade em pacientes com esclerose múltipla entre as latitudes Sul 18° e 30°

ABSTRACT

Objective:

Vitamin D has taken center stage in research and treatment of multiple sclerosis (MS). The objective of the present study was to assess the serum vitamin D levels of a large population of patients with MS and controls living in a restricted tropical area.

Methods:

Data from 535 patients with MS and 350 control subjects were obtained from 14 cities around the Tropic of Capricorn.

Results:

The mean serum 25-OH vitamin D level was 26.07 ± 10.27 ng/mL for the control subjects, and 28.03 ± 12.19 ng/mL for patients with MS. No correlation was observed between vitamin D levels and the disability of patients over the disease duration.

Conclusion:

At least for the region around the Tropic of Capricorn, serum levels of vitamin D typically are within the range of 20 to 30 ng/mL for controls and patients with MS.

Keywords:
vitamin D; multiple sclerosis; latitude

RESUMO

Objetivo:

Vitamina D assumiu um papel central na pesquisa e tratamento da esclerose múltipla (EM). O objetivo deste estudo foi avaliar os níveis séricos de vitamina D de pacientes com EM e controles que residem em uma área tropical.

Métodos:

Foram analisados dados de 535 pacientes com EM e 350 indivíduos controle em 14 cidades próximas ao Trópico de Capricórnio.

Resultados:

O valor médio da determinação de 25-OH vitamina D foi 26,07 ± 10,27 ng/mL para controles e 28,03 ± 12,19 ng/mL para pacientes com EM. Não houve correlação entre os níveis de vitamina D e o grau de incapacidade ao longo da duração da doença.

Conclusão:

Pelo menos na região que cerca o Trópico de Capricórnio, os níveis séricos de vitamina D estão entre valores de 20 a 30 ng/mL tanto para controles quanto para pacientes com EM.

Palavras-chave:
vitamina D; esclerose múltipla; latitude

There is no doubt that vitamin D has many biological effects on the human body. The potential effects of this hormone on bone metabolism, immunological responses and degenerative diseases has led to a dramatic surge of vitamin D testing in the fields of health and disease¹. Within multiple sclerosis (MS), a disease with marked predominance in areas of high latitude and long winters, serum assessment and supplementation of vitamin D rapidly took on great importance with regard to evaluating and treating MS patients. Nonetheless, while there is mounting evidence that vitamin D exerts broad regulatory effects on cells of the adaptive and innate immune systems^2,3, there is remarkably little evidence that treatment with vitamin D can influence MS evolution and prognosis^4,5,6,7. So far, no clinical trial has provided any clear evidence that vitamin D alone can alter the course of an extremely complex disease like MS. Other vitamins^8,9,10, genetic predisposition^11,12 and several environmental factors^13,14,15,16 may also play a substantial role in MS.

However strong the role of vitamin D in the orchestra of factors associated with MS may be, this might be better seen in high-latitude countries. The main source of vitamin D is through endogenous production, whereby the ultraviolet rays in sunlight irradiate the 7-dehydrocholesterol present in the skin, to generate cholecalciferol¹⁷, which is subsequently activated in the liver and kidney. Therefore, vitamin D levels may be higher in areas of the world where individuals have more exposure to sunlight, such as the tropics. The present study aimed to assess the potential effects of vitamin D levels on the development and progression of disability due to MS in an area at latitudes around the Tropic of Capricorn.

METHODS

The latitude of the Tropic of Capricorn is 23°27’ S and the geographic area included in the present study ranged from latitudes 18° to 30°S. Only patients and control subjects living in this restricted area were included in the study. This is a tropical to subtropical zone, with long summers and mild winters. No snow has ever been detected in any of the cities in this study. The length of the day varies between 10.30 hours (southern winter solstice) and 15.30 hours (southern summer solstice). Rainfall typically varies between 1,000 and 1,500 millimeters per year in this area. The 14 cities participating in the study were Blumenau, Curitiba, Florianopolis, Joinville, Juiz de Fora, Jundiai, Niteroi, Passo Fundo, Porto Alegre, Rio de Janeiro, Santos, Sao Paulo, Sorocaba, and Uberlandia. Their locations are shown on the map in Figure 1.

Figure 1
Schematic map of the location of the participant cities and their geographical information in relation to the Tropic of Capricorn (Blumenau, Curitiba, Florianopolis, Joinville, Juiz de Fora, Jundiai, Niteroi, Passo Fundo, Porto Alegre, Rio de Janeiro, Santos, Sao Paulo, Sorocaba, and Uberlandia).

This study was approved by the Ethics Committee. Neurologists from different cities within the established latitude levels collected data from their patients with MS and from control subjects of similar age and gender distribution. Patients were included in the MS group if they fulfilled the McDonald's criteria revised in 2005¹⁸. Patients and control subjects were only included in the study if they had not been taking vitamins (vitamin D or multivitamin compounds) as supplements for at least six months. Smoking habits were considered positive if the patient or control subject had smoked within the previous three years, independently of smoking at the time of blood collection for vitamin D assessment. No dietary restrictions were imposed on the subjects of this study, except for fasting for at least eight hours at the time of blood sampling. The 25-OH vitamin D levels were detected by means of chemiluminescent immunoassay. Although each participant's serum level was assessed in a clinical laboratory in his or her own city, the method used for this assessment was uniform.

Statistical analyses were performed blindly by one of the authors not involved in other phases of the project (PNS). The data were analyzed using GraphPad Prism, using two-way and one-way ANOVA, Spearman correlation, Kruskal-Wallis test, Mann-Whitney test and Student's t test. Significant values were considered to be those with p < 0.05.

RESULTS

Data were obtained from 350 controls (22% males, median age 36 years, smokers = 7.4%) and 535 patients with MS (25.9% males, median age 35 years, smokers = 14%). The mean serum 25-OH vitamin D level was 26.07 ± 10.27 ng/ml for the control subjects and 28.03 ± 12.19 ng/ml for patients with MS. Although the difference was considered to be significant through direct comparison using Student's t test (p = 0.01), the levels both for healthy subjects and for patients were within the range of 20–30 ng/ml, which can be considered to be low, but without characterizing vitamin D deficiency. Analysis on the patients and controls for values < 20 ng/ml or > 30 ng/ml did not show any significant difference between the groups (p = 0.10). The same was observed for all the data in this study, such that the majority of the participants systematically presented with serum vitamin D levels within the range of 20–30 ng/ml for all the parameters assessed (gender, age, MS variables, etc.). Fewer than 15% of the patients and controls showed serum vitamin D levels < 20 ng/ml. A summary of the data is presented in the Table and Figure 2.

Table
Vitamin D levels in serum of patients with multiple sclerosis and control subjects.

Variable	Population	Serum vitamin D (ng/ml) Average plasma levels	Smoking habits		EDSS
			Smokers	Non-smokers	≤ 5.0 (n = 480)	≥ 5.5 (n = 55)
Patients with MS	n = 535	28.03 ± 12.19	28.10 ± 12.42	27.61 ± 10.84	28.18 ± 12.14	26.69 ± 12.67
	M = 139
	F = 396
	med age = 35
Control subjects	n = 350	26.07 ± 10.27	26.09 ± 10.14	25.77 ± 11.90
	M = 79
	F = 271
	med age = 36

• MS: multiple sclerosis; M: males; F: females; med age: median age in years; EDSS: expanded disability scale score.

Figure 2
Levels of serum 25(OH) vitamin D in control subjects (n = 350) and patients with multiple sclerosis (n = 535). Average and median levels of vitamin D are similar for both groups and within the 20–30 ng/ml. According to different sources, this level is considered to be low, but not insufficient; while other sources state this level is normal. No correlation was observed between levels of vitamin D and disability over time.

No correlation was found between smoking and vitamin D levels among either the controls (p = 0.87) or the patients (p = 0.74). Through taking age to be a factor with the potential to modify vitamin levels, it was observed that, for the controls, there was a negative correlation between age and serum 25(OH) vitamin D levels (p = 0.01). The same was not observed for patients, for whom age did not seem to affect serum vitamin D levels (p = 0.3). However, once again, even though the serum vitamin D levels were significantly different, the patients and controls typically showed levels within the range of 20-30 ng/ml.

Men showed significantly higher vitamin D levels than women, among the patients (p = 0.005), and borderline higher values among the controls (p = 0.06). Again, serum vitamin D levels were mostly within the 20-30 ng/ml range for both genders and there was no difference between the groups regarding values < 20 ng/ml or > 30 ng/ml.

Disease duration (p = 0.20) and disability (p = 0.39) measured using the Expanded Disability Score Scale¹⁸ (EDSS) did not show correlations with the serum vitamin D levels in patients with MS (Figure 2). Aggressiveness of the disease, measured as higher EDSS values with shorter disease duration, was not shown to differ between patients whose serum vitamin D levels were higher or lower in this study (p = 0.65) (Figure 2).

DISCUSSION

Sunlight is essential to life on Earth. Ultraviolet radiation, infrared and visible light are all part of the solar light spectrum, and around 90% of the radiation received on Earth arrives in the form of ultraviolet light¹⁹. Ultraviolet radiation influences vitamin D synthesis and it is beneficial for complex metabolic pathways of homeostasis in the human body. At the same time, ultraviolet radiation is a very important environmental hazard for human skin, and exposure needs to be restricted to a few hours a day. Early morning and late afternoon are the best times of the day for exposure to the sun in the tropics and many people take daily walks or do activities at these times. This is considered to be good for health, and is recommended by many health-care personnel.

Although the Endocrine Medical Society recommends vitamin D levels of at least 30 ng/ml²⁰, the Food and Nutrition Board considers that serum vitamin D levels > 20 ng/ml are adequate²¹. The vast majority of the participants in this study presented with levels > 20 ng/ml.

The present study showed that there were no differences in the average vitamin D levels assessed, between healthy controls and patients with MS. These subjects were not supplementing their diets with vitamins and were continuously exposed to the mild climate at latitudes around the Tropic of Capricorn, between 18° and 30° South. Thus, exposure to the sun may have played an important part in maintaining uniform vitamin D levels among the participants of this study. However, the authors are aware that daily sun exposure was not a parameter assessed in this study, and this may be a limitation to interpretation of results. Nevertheless, the large number of patients and controls enrolled in this study may overcome the limitations of measuring daily sun exposure. In addition, results were not different in any of the cities or between control subjects and patients, which further suggests that sun exposure and vitamin D were average for these individuals.

It is important to remember that ultraviolet radiation has other effects beyond metabolism of vitamin D that might explain the beneficial effects of living in the tropics. Ultraviolet radiation induces cytokines with immunosuppressive behavior (CXCL12), affects the non-vitamin D pathway in dendritic cells, and induces production of the immunoregulatory molecule cis-urocanic acid^22,23. An MRI study on people with MS showed that sun exposure, independently of vitamin D levels, was associated with better outcomes²⁴. A study on the age of onset of MS did not show correlation with vitamin D levels²⁵. A very recent multicenter study showed that, although potentially present, the relationship between vitamin D levels and the conversion from clinically isolated syndrome into clinically defined MS may be attenuated by other factors²⁶. In fact, the Cochrane database states that “the current level of evidence for the effectiveness of vitamin D supplementation in the management of people with MS does not, at present, allow confident decision-making about the use of vitamin D in MS”²⁷.

Again, in the region of the Tropic of Capricorn, Australian researchers have not found that vitamin D supplementation has any effect on patients with MS²⁸. Serum vitamin D levels may have been a simplistic way to assess a very complex regulatory pathway in MS. No clinical trial has shown any success from vitamin D supplementation for controlling MS. Independently of vitamin D production and serum vitamin D levels, sunlight and particularly ultraviolet radiation may be responsible for combating disease incidence and progression, with a positive link with latitude. This has also been stated by other researchers^29,30,31. Despite a few hundred systematic reviews and meta-analyses, there is no highly convincing evidence of any clear role for vitamin D in controlling any disease outcome³². In fact, vitamin D may be a surrogate marker for ill health, rather than the cause of diseases it is blamed for.

The results shown here may not be reproducible in studies carried out in the higher northern latitudes. There have been studies showing, for example, a correlation between EDSS and serum vitamin D levels in Europe and North America^33,34. There have also been studies showing a potential role for serum vitamin D levels for MS relapse prevention in some populations^35,36,37, and control over lesions seen on MRI in some countries³⁸. The authors of the present study do not dispute the role of vitamin D in human health and the immune system. However, we question whether results from all parts of the world would be the same if vitamin D were the only parameter of importance in such a complex disease. It is important to highlight that many MS studies carried out in Latin America show results differing from those published by our peers at higher latitudes in the northern hemisphere. In Mexico, a country crossed by the Tropic of Cancer, vitamin D levels do not seem to differ between controls and MS patients either^39,40. A recent Brazilian study of 67 patients with MS showed that, although there was an association of low levels of vitamin D and MS relapses, no correlation between levels of vitamin D and disability could be observed⁴¹. In the Netherlands, similar results were found regarding the lack of clear association between levels of vitamin D and disability status in MS⁴².

Multiple sclerosis must not be seen as a simple disease, explained by deficiency of a particular vitamin, or having a uniform profile worldwide. At least for the latitudes of 18° to 30° South, serum vitamin D levels did not differ between controls and MS patients, and were not related to worse disease evolution.

Acknowledgements

The authors acknowledge the essential help of Mr David G. Elliff for technical design of Figure 1 and for revising the English language of the paper.

References

• ¹
  Glendenning P, Inderjeeth CA. Controversy and consensus regarding vitamin D: recent methodological changes and the risks and benefits ofvitamin D supplementation. Crit Rev Clin Lab Sci. 2016;53(1):13-28. doi:10.3109/10408363.2015.1074157
  » https://doi.org/10.3109/10408363.2015.1074157
• ²
  Calton EK, Keane KN, Newsholme P, Soares MJ. The impact of vitamin D levels on inflammatory status: a systematic review of immune cell studies. PLoS One. 2015;10(11):e0141770. doi:10.1371/journal.pone.0141770
  » https://doi.org/10.1371/journal.pone.0141770
• ³
  Shirvani-Farsani Z, Behmanesh M, Mohammadi SM, Naser Moghadasi A. Vitamin D levels in multiple sclerosis patients: association with TGF-β2, TGF-βRI, and TGF-βRII expression. Life Sci. 2015;134:63-7. doi:10.1016/j.lfs.2015.05.017
  » https://doi.org/10.1016/j.lfs.2015.05.017
• ⁴
  James E, Dobson R, Kuhle J, Baker D, Giovannoni G, Ramagopalan SV. The effect of vitamin D-related interventions on multiple sclerosis relapses: a meta-analysis. Mult Scler. 2013;19(12):1571-9. doi:10.1177/1352458513489756
  » https://doi.org/10.1177/1352458513489756
• ⁵
  Nikanfar M, Taheri-Aghdam AA, Yazdani M, Shaafi S, Masoudian N, Akbari H et al. Serum 25(OH) Vitamin D levels is not associated with disability in multiple sclerosis patients: a case-control study. Iran J Neurol. 2015;14(1):17-21.
• ⁶
  Røsjø E, Steffensen LH, Jørgensen L, Lindstrøm JC, Šaltytė Benth J, Michelsen AE et al. Vitamin D supplementation and systemic inflammation in relapsing-remitting multiple sclerosis. J Neurol. 2015;262(12):2713-21. doi:10.1007/s00415-015-7902-5
  » https://doi.org/10.1007/s00415-015-7902-5
• ⁷
  Pakpoor J, Ramagopalan S. Evidence for an association between vitamin D and multiple sclerosis. Curr Top Behav Neurosci. 2015;26:105-15. doi:10.1007/7854_2014_358
  » https://doi.org/10.1007/7854_2014_358
• ⁸
  Løken-Amsrud KI, Myhr KM, Bakke SJ, Beiske AG, Bjerve KS, Bjørnarå BT et al. Alpha-tocopherol and MRI outcomes in multiple sclerosis: association and prediction. PLoS One. 2013;8(1):e54417. doi:10.1371/journal.pone.0054417
  » https://doi.org/10.1371/journal.pone.0054417
• ⁹
  Fragoso YD, Stoney PN, McCaffery PJ. The evidence for a beneficial role of vitamin A in multiple sclerosis. CNS Drugs. 2014;28(4):291-9. doi:10.1007/s40263-014-0148-4
  » https://doi.org/10.1007/s40263-014-0148-4
• ¹⁰
  Røsjø E, Myhr KM, Løken-Amsrud KI, Bakke SJ, Beiske AG, Bjerve KS et al. Increasing serum levels of vitamin A, D and E are associated with alterations of different inflammation markers in patients with multiple sclerosis. J Neuroimmunol. 2014;271(1-2):60-5. doi:10.1016/j.jneuroim.2014.03.014
  » https://doi.org/10.1016/j.jneuroim.2014.03.014
• ¹¹
  Cree BA. Multiple sclerosis genetics. Handb Clin Neurol. 2014;122:193-209. doi:10.1016/B978-0-444-52001-2.00009-1
  » https://doi.org/10.1016/B978-0-444-52001-2.00009-1
• ¹²
  Hollenbach JA, Oksenberg JR. The immunogenetics of multiple sclerosis: A comprehensive review. J Autoimmun. 2015;64:13-25. doi:10.1016/j.jaut.2015.06.010
  » https://doi.org/10.1016/j.jaut.2015.06.010
• ¹³
  Belbasis L, Bellou V, Evangelou E, Ioannidis JP, Tzoulaki I. Environmental risk factors and multiple sclerosis: an umbrella review of systematic reviews and meta-analyses. Lancet Neurol. 2015;14(3):263-73. doi:10.1016/S1474-4422(14)70267-4
  » https://doi.org/10.1016/S1474-4422(14)70267-4
• ¹⁴
  Fragoso YD. Modifiable environmental factors in multiple sclerosis. Arq Neuropsiquiatr. 2014;72(11):889-94. doi:10.1590/0004-282X20140159
  » https://doi.org/10.1590/0004-282X20140159
• ¹⁵
  Galland L. The gut microbiome and the brain. J Med Food. 2014;17(12):1261-72. doi:10.1089/jmf.2014.7000
  » https://doi.org/10.1089/jmf.2014.7000
• ¹⁶
  Heydarpour P, Amini H, Khoshkish S, Seidkhani H, Sahraian MA, Yunesian M. Potential impact of air pollution on multiple sclerosis in Tehran, Iran. Neuroepidemiology. 2014;43(3-4):233-8. doi:10.1159/000368553
  » https://doi.org/10.1159/000368553
• ¹⁷
  Liu J. Vitamin D content of food and its contribution to vitamin D status: a brief overview and Australian focus. Photochem Photobiol Sci. 2012;11(12):1802-7. doi:10.1039/c2pp25150g
  » https://doi.org/10.1039/c2pp25150g
• ¹⁸
  Kurtzke JF. Rating neurologic impairment in multiple sclerosis: an expanded disability status scale (EDSS). Neurology. 1983;33(11):1444-52. doi:10.1212/WNL.33.11.1444
  » https://doi.org/10.1212/WNL.33.11.1444
• ¹⁹
  Osmola-Mańkowska A, Silny W, Dańczak-Pazdrowska A, Olek-Hrab K, Mańkowski B, Osmola K. The sun-our friend or foe? Ann Agric Environ Med. 2012;19:805-9.
• ²⁰
  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. doi:10.1210/jc.2011-0385
  » https://doi.org/10.1210/jc.2011-0385
• ²¹
  Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: in National Academy Press, USA 2010.
• ²²
  Lucas RM, Byrne SN, Correale J, Ilschner S, Hart PH. Ultraviolet radiation, vitamin D and multiple sclerosis. Neurodegener Dis Manag. 2015;5(5):413-24. doi:10.2217/nmt.15.33
  » https://doi.org/10.2217/nmt.15.33
• ²³
  Byrne SN. How much sunlight is enough? Photochem Photobiol Sci. 2014;13(6):840-52. doi:10.1039/c4pp00051j
  » https://doi.org/10.1039/c4pp00051j
• ²⁴
  Zivadinov R, Treu CN, Weinstock-Guttman B, Turner C, Bergsland N, O'Connor K et al. Interdependence and contributions of sun exposure and vitamin D to MRI measures in multiple sclerosis. J Neurol Neurosurg Psychiatry. 2013;84(10):1075-81. doi:10.1136/jnnp-2012-304661
  » https://doi.org/10.1136/jnnp-2012-304661
• ²⁵
  Brenton JN, Koenig S, Goldman MD. Vitamin D status and age of onset of demyelinating disease. Mult Scler Relat Disord. 2014;3(6):684-8. doi:10.1016/j.msard.2014.07.004
  » https://doi.org/10.1016/j.msard.2014.07.004
• ²⁶
  Kuhle J, Disanto G, Dobson R, et al. Conversion from clinically isolated syndrome to multiple sclerosis: A large multicentre study. Mult Scler. 2015;21(8):1013-24. doi:10.1177/1352458514568827
  » https://doi.org/10.1177/1352458514568827
• ²⁷
  Jagannath VA, Fedorowicz Z, Asokan GV, Robak EW, Whamond L et al. Vitamin D for the management of multiple sclerosis. Cochrane Database Syst Rev. 2010;12(12):CD008422. doi:10.1002/14651858.CD008422.pub2
  » https://doi.org/10.1002/14651858.CD008422.pub2
• ²⁸
  Stein MS, Liu Y, Gray OM, Baker JE, Kolbe SC, Ditchfield MR et al. A randomized trial of high-dose vitamin D2 in relapsing-remitting multiple sclerosis. Neurology. 2011;77(17):1611-8. doi:10.1212/WNL.0b013e3182343274
  » https://doi.org/10.1212/WNL.0b013e3182343274
• ²⁹
  Hart PH. Vitamin D supplementation, moderate sun exposure, and control of immune diseases. Discov Med. 2012;13(73):397-404.
• ³⁰
  Lucas RM, Ponsonby AL, Dear K, Valery PC, Pender M P, Taylor BV et al. Sun exposure and vitamin D are independent risk factors for CNS demyelination. Neurology. 2011;76(6):540-8. doi:10.1212/WNL.0b013e31820af93d
  » https://doi.org/10.1212/WNL.0b013e31820af93d
• ³¹
  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. doi:10.1016/S2213-8587(13)70165-7
  » https://doi.org/10.1016/S2213-8587(13)70165-7
• ³²
  Theodoratou E, Tzoulaki I, Zgaga L, Ioannidis JP. Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of observational studies and randomised trials. BMJ. 2014;348:g2035. doi:10.1136/bmj.g2035
  » https://doi.org/10.1136/bmj.g2035
• ³³
  Thouvenot E, Orsini M, Daures JP, Camu W. Vitamin D is associated with degree of disability in patients with fully ambulatory relapsing-remitting multiple sclerosis. Eur J Neurol. 2015;22(3):564-9. doi:10.1111/ene.12617
  » https://doi.org/10.1111/ene.12617
• ³⁴
  Fitzgerald KC, Munger KL, Köchert K, Arnason BG, Comi G, Cook S et al. Association of vitamin D levels with multiple sclerosis activity and progression in patients receiving interferon beta-1b. JAMA Neurol. 2015;72(12):1458-65. doi:10.1001/jamaneurol.2015.2742
  » https://doi.org/10.1001/jamaneurol.2015.2742
• ³⁵
  Simpson S Jr, Taylor B, Blizzard L, Ponsonby AL, Pittas F, Tremlett H et al. Higher 25-hydroxyvitamin D is associated with lower relapse risk in multiple sclerosis. Ann Neurol. 2010;68(2):193-203. doi:10.1002/ana.22043
  » https://doi.org/10.1002/ana.22043
• ³⁶
  Pierrot-Deseilligny C, Rivaud-Péchoux S, Clerson P, Paz R, Souberbielle JC. Relationship between 25-OH-D serum level and relapse rate in multiple sclerosis patients before and after vitamin D supplementation. Ther Adv Neurol Disorder. 2012;5(4):187-98. doi:10.1177/1756285612447090
  » https://doi.org/10.1177/1756285612447090
• ³⁷
  Scott TF, Hackett CT, Dworek DC, Schramke CJ. Low vitamin D level is associated with higher relapse rate in natalizumab treated MS patients. J Neurol Sci. 2013;330(1-2):27-31. doi:10.1016/j.jns.2013.03.020
  » https://doi.org/10.1016/j.jns.2013.03.020
• ³⁸
  Mowry EM, Waubant E, McCulloch CE, Okuda DT, Evangelista AA, Lincoln RR et al. Vitamin D status predicts new brain magnetic resonance imaging activity in multiple sclerosis. Ann Neurol. 2012;72(2):234-40. doi:10.1002/ana.23591
  » https://doi.org/10.1002/ana.23591
• ³⁹
  Rito Y, Flores J, Fernández Aguilar Á, Escalante Membrillo C, Gutiérrez Lanz E, Barboza MA et al. Vitamin D in multiple sclerosis patients: Not the same risk for everybody. Mult Scler. 2016;22(1):126-7. doi:10.1177/1352458515576986
  » https://doi.org/10.1177/1352458515576986
• ⁴⁰
  Espinosa-Ramírez G, Ordoñez G, Flores-Rivera J, Sotelo J. Sunlight exposure and multiple sclerosis in a tropical country. Neurol Res. 2014;36(7):647-50. doi:10.1179/1743132813Y.0000000307
  » https://doi.org/10.1179/1743132813Y.0000000307
• ⁴¹
  Becker J, Callegaro D, Lana-Peixoto MA, Talim N, Vidaletti T, Corrêa MP et al. Hypovitaminosis D association with disease activity in relapsing remitting multiple sclerosis in Brazil. J Neurol Sci. 2016;363:236-9. doi:10.1016/j.jns.2016.02.064
  » https://doi.org/10.1016/j.jns.2016.02.064
• ⁴²
  Muris AH, Smolders J, Rolf L, Klinkenberg LJ, van der Linden N, Meex S et al. Vitamin D status does not affect disability progression of patients with multiple sclerosis over three year follow-up. PLoS One. 2016;11(6):e0156122. doi:10.1371/journal.pone.0156122
  » https://doi.org/10.1371/journal.pone.0156122

Publication Dates

• Publication in this collection
  Jan 2017

History

• Received
  07 Aug 2016
• Reviewed
  26 Aug 2016
• Accepted
  09 Aug 2016