Background: The link between autoimmune thyroid diseases and Vitamin D deficiency has been reported. However, there are controversies in this regard. We conducted a double-blind randomized placebo-controlled clinical trial to investigate the effect of Vitamin D deficiency treatment on thyroid function and autoimmunity marker (thyroid peroxidase antibody [TPO-Ab]) in patients with Hashimoto's thyroiditis.
Materials and methods: Fifty-six patients with Hashimoto's thyroiditis and Vitamin D deficiency (25-hydroxyvitamin D level ≤20 ng/mL) were randomly allocated into two groups to receive Vitamin D (50000 IU/week, orally) or placebo for 12 weeks, as Vitamin D-treated (n = 30) and control (n = 26) groups, respectively. TPO-Ab, thyroid-stimulating hormone (TSH), parathormone, calcium, albumin, and creatinine concentrations were compared before and after trial between and within groups. The data were presented as mean (standard error [SE]) and analyzed by appropriate tests.
Results: Mean (SE) of Vitamin D was increased in Vitamin D-treated group (45.5 [1.8] ng/mL vs. 12.7 [0.7] ng/mL, P = 0.01). Mean (SE) of TPO-Ab did not significantly change in both groups (734 [102.93] IU/mL vs. 820.25 [98.92] IU/mL, P = 0.14 in Vitamin D-treated and 750.03 [108.7] [IU/mL] vs. 838.07 [99.4] [IU/mL] in placebo-treated group, P = 0.15). Mean (SE) of TSH was not changed in both groups after trial, P = 0.4 and P = 0.15 for Vitamin D-treated and control groups, respectively. No significant difference was observed between two study groups in none studied variables (P > 0.05).
Conclusion: Vitamin D treatment in Vitamin D deficient patients with Hashimoto's thyroiditis could not have significant effect on thyroid function and autoimmunity.
Keywords: Autoimmune thyroiditis; Iran; Vitamin D deficiency; clinical trial; peroxidase; thyroid-stimulating hormone.