Low Serum Vitamin D Is Associated with Anti-Thyroid Peroxidase Antibody in Autoimmune Thyroiditis

PURPOSE: The association between autoimmune thyroid diseases (AITDs) and vitamin D deficiency is controversial. We aimed to evaluate the relationship between serum 25-hydroxy-vitamin D(3) [25(OH)D(3)] and anti-thyroid antibody levels. MATERIALS AND METHODS: 25(OH)D(3), anti-thyroid antibodies, and thyroid function measured in 304 patients who visited the endocrinology clinic were analyzed. The patients were subgrouped into the AITDs or non-AITDs category according to the presence or absence of anti-thyroid antibodies. The relationship between anti-thyroid peroxidase antibody (TPOAb) and 25(OH)D(3) was evaluated. RESULTS: The patients with elevated anti-thyroid antibodies had lower levels of serum 25(OH)D(3) than those who did not (12.6±5.5 ng/mL vs. 14.5±7.3 ng/mL, respectively, p<0.001). Importantly, after adjusting for age, sex, and body mass index, a negative correlation (r=-0.252, p<0.001) was recognized between 25(OH)D(3) and TPOAb levels in the AITDs group, but this correlation did not exist in the non-AITDs group (r=0.117, p=0.127). 25(OH)D(3) level was confirmed as an independent factor after adjusting for co-factors that may affect the presence of TPOAb in the AITDs group. CONCLUSION: 25(OH)D(3) level is an independent factor affecting the presence of TPOAb in AITDs. The causal effect of 25(OH)D(3) deficiency to AITDs is to be elucidated.