Prevalence of Vitamin D Deficiency and its Association with Thyroid Autoimmunity and Thyroid Hormones in Newly Diagnosed Patients with Autoimmune Thyroid Disease (AITD)

A BSTRACT Objective: To look for the prevalence of vitamin D deficiency (VDD) and its association with anti-TPO antibody and thyroid hormones (FT3, FT4, and TSH) levels in newly diagnosed patients with autoimmune thyroid disease (AITD). Methods: In this case-control study, new-onset AITD hypothyroidism/hyperthyroidism patients (anti-TPO-Ab levels >60 IU/ml) were recruited (n = 50). Fifty age, sex, and BMI-matched euthyroid healthy individuals were taken as controls. Detailed clinical examination and necessary investigations such as serum FT3, FT4, TSH, anti-TPO-Ab, 25 OHD (25 hydroxy vitamin D), and iPTH were measured. Results: The prevalence of VDD (25 OHD <20 ng/ml) was significantly higher in all AITD cases than that of controls (62% vs. 26%, P = 0.0003). No significant difference was found in the occurrence of VDD between hypothyroid and hyperthyroid AITD patients (69% vs. 50%, P = 0.189). AITD patients with VDD have significantly higher levels of anti-TPO-Ab (702.34 ± 498.54 IU/ml) as compared to vitamin D non deficient AITD subjects (234.64 ± 166.82 IU/ml) ( P = 0.0003). Anti-TPO-Ab levels correlated inversely and significantly with 25 OHD levels among all AITD subjects (r = -0.610, P < 0.0001) without any significant correlation with thyroid hormones. Multiple linear regression analysis revealed that only serum 25 OHD had a significant inverse association with anti-TPO-Ab levels (β = -0.323; P = 0.036) but not with thyroid hormones. Conclusions: Vitamin D deficiency is commonly found in AITD patients. There is a significant negative association between vitamin D levels and anti-TPO-Ab titers suggesting a link between low vitamin D and AITD.