BACKGROUND: Alopecia areata is postulated to be an autoimmune disease of which vitamin D may play a role being found in the immune system and hair.

OBJECTIVE: To determine the association between serum 25-hydroxyvitamin D levels in patients with alopecia areata compared with healthy controls.

METHODS: Observational studies on association of vitamin D levels on alopecia areata compared to healthy controls were obtained from all published articles until July 2018 on MEDLINE, Cochrane Library, TRIP, HERDIN, and Google. Review Manager 5.3 was used for the meta-analysis.

RESULTS: The search strategy yielded 13 qualified articles for the full-length review and 11 studies, containing 916 patients, were included in the meta-analysis using the pooled random effects model. The pooled mean difference of the serum 25-hydroxyvitamin D levels between alopecia areata patients and healthy controls was -9.55 (95% CI, -10.51 to -8.59) with heterogeneity (I2=85%).

CONCLUSION: In conclusion, there were reduced levels of serum 25-hydroxyvitamin D levels in alopecia areata compared to healthy controls and vitamin D deficiency was more prevalent in alopecia areata compared to healthy controls. There was also a trend of lower vitamin D levels in the more severe forms of alopecia.