Serum 25 hydroxyvitamin D in non-scarring alopecia: A systematic review and meta-analysis.

INTRODUCTION: Non-scarring alopecia mainly includes androgenetic alopecia (AGA), female pattern hair loss (FPHL), alopecia areata (AA), telogen effluvium (TE), anagen effluvium (AE) and so on. Many studies had investigated the serum 25-hydroxyvitamin D level and vitamin D deficiency of patients with these diseases, but opinions varied, and no conclusion was reached. METHODS: Relevant articles were retrieved through PubMed, Web of Science, EMBASE, Cochrane Library, China National Knowledge Infrastructure (CNKI) and other databases. Serum 25-hydroxyvitamin D [25(OH) D] levels and vitamin D deficiency were used as our primary outcome. The odds ratio (OR) and the standardized mean difference (SMD) with 95% confidence interval were both examined for vitamin D deficiency and levels. RESULTS: Our meta-analysis had included a total of 3374 non-scarring alopecia patients and 7296 healthy controls from 23 studies through the inclusion criteria and exclusion criteria. We found non-scarring alopecia had decreased serum 25(OH)D level (WMD -7.29; 95% CI -9.21, -5.38) and increased vitamin D deficiency incidence (OR 3.11 95% CI 2.29, 4.22), compared with healthy controls. This meta-analysis chose to conduct random-effect model and subgroup analysis, because of the high heterogeneity (serum 25(OH)D level: I 2 = 95%, vitamin D deficiency: I 2 = 0%). CONCLUSION: Patients with non-scarring alopecia (including AA, FPHL, AGA and TE) have insufficient serum level of 25(OH)D and increased incidence of vitamin D deficiency. Vitamin D supplementation and monitoring for vitamin D deficiency may be helpful in treating non-scarring alopecia.