Background
Alopecia areata (AA) is a frequent autoimmune disease, the pathogenesis of which is still unknown. Androgenetic alopecia (AGA) is a noncicatricial type of patterned hair loss. Expression of vitamin D receptors (VDRs) on keratinocytes is essential for maintenance of normal hair cycle, especially anagen initiation.

Objective
To assess VDRs in the skin and blood of AA and AGA patients, in order to evaluate their possible role in these hair diseases.

Methods
This study recruited 20 patients with AA, 20 patients with AGA, and 20 healthy controls. Blood samples and lesional scalp biopsies were taken from all participants for detection of VDR levels.

Results
Serum and tissue VDR levels were lower in AA as well as AGA patients when compared to controls (P = 0.000). Serum and tissue VDR were positively correlated in each group. Tissue VDR was significantly lower in female patients with AA than males (P = 0.046) although serum and tissue VDR levels were significantly higher in female AGA patients than males (P = 0.004).

Conclusion
This study suggests an important role for VDR in the pathogenesis of AA and AGA through documenting lower serum and tissue VDR levels in AA and AGA patients in comparison with controls.