Effects of vitamin D treatment on thyroid function and autoimmunity markers in patients with Hashimoto's thyroiditis—A meta‐analysis of randomized controlled trials

Introduction Recent evidence suggested that vitamin D deficiency was associated with Hashimoto's thyroiditis (HT) pathogenesis and thyroid hypofunction. This study aimed to investigate whether vitamin D supplementation would be effective in the prevention and progression of hypothyroidism in patients with HT. Methods PubMed, Embase and the Cochrane library were searched for randomized controlled trials (RCTs) and prospective cohort studies published from inception to August 2021. Results A total of 7 cohorts of patients from six clinical trials with 258 patients with HT were included. Significant difference was found (WMD = 19.00, 95% CI: 12.43, 25.58, p < 0.001; I2 = 90.0%, pheterogeneity < 0.001) between the vitamin D group and control group in serum 25-hydroxyvitamin D level. And the combined results indicated vitamin D supplementation significantly reduced the level of thyroid peroxidase antibodies (TPO-Ab) compared to the control group (WMD = −158.18, 95% CI: −301.92, −14.45, p = 0.031; I2 = 68.8%, pheterogeneity = 0.007). Whereas no significant differences were found on the levels of thyroid-stimulating hormone (TSH), free triiodothyronine (FT3), free thyroxine (FT4) compared to the control group (p > 0.05). What is New and Conclusion Our study demonstrated that vitamin D treatment might significantly increase the serum 25(OH)D levels and produce changes in TPO-Ab titres. No significant association was found between serum vitamin D treatment and the levels of TG-Ab, TSH, FT3 and FT4, suggesting that vitamin D is not associated with the function of the thyroid in patients with HT.