الفهرس 
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Abstract
Alopecia areata is a chronic relapsing immune-mediated inflammatory disorder that affects hair follicles resulting in non- scarring hair loss. The severity of the disorder ranges from small patches of alopecia on any hair-bearing area to the complete loss of scalp, eyebrow, eyelash, and body hair. The etiology of AA is not known exactly; however factors such as genetic predisposition, autoimmunity, and environmental factors have been suggested. The autoimmune etiology has been proposed on the basis of its association with various autoimmune diseases, the presence of autoantibodies, the presence of inflammatory lymphocytes around and within affected hair follicles and the ability to promote hair regrowth with the use of immunosuppressive agents. Vitamin D is a fat soluble vitamin that has three sources; endogenous synthesis in the skin, which is induced by ultraviolet B radiation, dietary intake and vitamin D supplementation. The main function of vitamin D is to keep normal calcium and phosphorus levels in the body to enable normal mineralization of bone, maintains strong teeth and nail.
Vitamin D has other roles in the body, including modulation of cell growth, neuromuscular function, immune function, and reduction of inflammation. Research also suggests that vitamin D may provide protection from cardiovascular diseases and hypertension. Vitamin D is a modulator of both the innate and adaptive immune systems through its varied effects on T and B lymphocytes, DCs, and macrophages. A connection between some autoimmune diseases. including type I diabetes mellitus, rheumatoid arthritis, systemic lupus erythematosis, vitiligo, psoriasis, multiple sclerosis and inflammatory bowel disease, and vitamin D deficiency has been reported. This finding suggests that vitamin D deficiency might be an environmental trigger for the induction of autoimmunity. On the other hand, it has been demonstrated that VDRs are strongly expressed in the key structures of hair follicles. Expression of VDRs in keratinocytes is necessary for maintenance of the normal hair cycle. It has also been shown that a lack of VDRs reduces epidermal differentiation and hair follicle growth. Our study aimed at measuring serum 25(OH)D level in patients with AA in comparison to controls in an attempt to evaluate its role in the pathogenesis of the disease. The study recruited 60 subjects, 30 AA patients and 30 controls. All patients were subjected to detailed history taking and examination. Venous blood samples were taken from all subjects to assess serum 25(OH)D level. The obtained data was tabulated and statistically analyzed. The results revealed significant decrease in serum 25(OH)D levels in AA patients in comparison to controls. Low vitamin D level (insufficiency/deficiency) was present in 83.3% of AA patients compared with only 23.3% healthy controls.
There was statistically significant association between the vitamin D status and severity of AA and pattern of hair loss. There was statistically significant negative association between serum 25(OH) D levels and age of patients. There was no statistically significant association between the vitamin D status and gender of patients, disease duration, nail affection, recurrence and family history of AA.