1 McElwee K.J.

Gilhar A.

Tobin D.J.

et al. What causes alopecia areata?. 2 Kriegel M.A.

Manson J.E.

Costenbader K.H. Does vitamin D affect risk of developing autoimmune disease?: a systematic review. , 3 Upala S.

Sanguankeo A. Low 25-hydroxyvitamin D levels are associated with vitiligo: a systematic review and meta-analysis. Alopecia areata (AA) is a T cell–mediated autoimmune disease that causes nonscarring hair loss.Some autoimmune diseases are associated with a vitamin D deficiency, including inflammatory bowel disease, multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosus, and vitiligo.Previous studies that evaluated vitamin D levels in patients with AA have reached inconsistent conclusions. This study aimed to perform a systematic review and meta-analysis on the association between vitamin D levels and AA.

This study covered all literature published before May 15, 2017. We included case-control studies in English that compared the prevalence of vitamin D deficiency or vitamin D levels in patients with AA and in controls. Review articles, case reports, and conference reports were excluded. Odds ratios were used to compare the prevalence of vitamin D deficiency in patients with AA and controls. Continuous data were analyzed using standardized mean difference, which accounted for the varied and nonstandardized outcomes across studies. A random effects model was used for all studies because of greater heterogeneity. All analyses were performed using Comprehensive Meta-Analysis software (version 3; Biostat, Inc, Englewood, NJ).

Fig 1 Forest plots. The forest plots showed that patients with alopecia areata had a significantly higher prevalence of 25-hydroxyvitamin D deficiency than those in the control group. (Odds ratio = 4.86 [95% confidence interval 1.60-14.76], I2 = 89.0%.) Fig 2 Forest plots. The forest plots showed that patients with alopecia areata had a significantly lower level of 25-hydroxyvitamin D than those in the control group. (Standardized mean difference = −1.08 [95% confidence interval −1.58 to −0.58], I2 = 89.5%.) Std, Standardized. Eleven studies including 456 patients with AA met the inclusion criteria. Eight of the 11 studies provided data on the prevalence of vitamin D deficiency; 5 of these 8 studies showed a higher prevalence of vitamin D deficiency in patients with AA. Nine of the 11 studies presented vitamin D levels; of these studies, 8 demonstrated significantly lower levels of vitamin D in patients with AA than in the control group. Patients with AA had a significantly higher prevalence of 25-hydroxyvitamin D deficiency (OR = 4.86 [95% confidence interval {CI} 1.60-14.76]; Fig 1 ) and lower levels of 25-hydroxyvitamin D (standardized mean difference = -1.08 [95% CI -1.58 to -0.58]; Fig 2 ) than those in the control group.

H ) 1 cytokine secretion and stimulates T H 2 cytokine secretion. 4 Hewison M. An update on vitamin D and human immunity. H 2 phenotype suppresses T H 1-mediated autoimmune diseases. 4 Hewison M. An update on vitamin D and human immunity. , 5 Di Rosa M.

Malaguarnera M.

Nicoletti F.

et al. Vitamin D3: a helpful immuno-modulator. H 17 cells, which are potent inducers of autoimmune diseases. 4 Hewison M. An update on vitamin D and human immunity. , 5 Di Rosa M.

Malaguarnera M.

Nicoletti F.

et al. Vitamin D3: a helpful immuno-modulator. 4 Hewison M. An update on vitamin D and human immunity. , 5 Di Rosa M.

Malaguarnera M.

Nicoletti F.

et al. Vitamin D3: a helpful immuno-modulator. Studies have shown that 1,25-dihydroxyvitamin D inhibits T helper (T) 1 cytokine secretion and stimulates T2 cytokine secretion.Polarization of the immune system toward the T2 phenotype suppresses T1-mediated autoimmune diseases.In addition, 1,25-dihydroxyvitamin D inhibits the function of T17 cells, which are potent inducers of autoimmune diseases.Additionally, it enhances regulatory T cells, which play a key role in suppressing autoimmune responses.

Our study had several limitations. The baseline characteristics of the included subjects were heterogeneous. Serum 25-hydroxyvitamin D concentration is modulated by sex, age, ethnicity, comorbidity, diet, sun exposure level, season of blood sampling, and treatments, such as phototherapy. Subgroup analysis and metaregression were not performed because only a few studies provided detailed data on disease pattern and severity.

In conclusion, our meta-analysis found that patients with AA have a higher prevalence of 25-hydroxyvitamin D deficiency and lower 25-hydroxyvitamin D levels than the control group. Further research is needed to elucidate the underlying mechanisms and assess the efficacy of vitamin D supplementation in treating AA.

Article Info Footnotes Funding sources: None. Conflicts of interest: None declared. Identification DOI: https://doi.org/10.1016/j.jaad.2017.07.051 Copyright © 2017 by the American Academy of Dermatology, Inc. ScienceDirect Access this article on ScienceDirect

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