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; I (2 )= 90.0%, p (heterogeneity )< 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; I (2 )= 68.8%, p (heterogeneity )= 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.