The association between vitamin D and hypothyroidism: a systematic review and meta-analysis

Hypothyroidism is a prevalent pathological condition resulting from insufficient thyroid hormone production by the thyroid gland. The potential role of vitamin D supplementation in the prevention and treatment of various diseases is well-recognized. However, its specific impact on individuals with hypothyroidism remains unclear.

This systematic review follows the PRISMA 2020 flowchart. The review aimed to evaluate the effects of vitamin D on hypothyroidism by synthesizing available evidence. A comprehensive search was conducted across several databases, including PubMed, Embase, Web of Science, and the Cochrane Library, up to February 2024. Standard mean differences (SMDs) and odds ratios (ORs) with their 95% confidence intervals (CIs) were calculated using fixed or random effects models, based on heterogeneity assessed by the I² statistic. Sensitivity analyses and assessments of publication bias were also performed. The certainty of evidence was evaluated using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system.

A total of 5 randomized controlled trials and 11 observational studies, encompassing 4,152 subjects, met the inclusion criteria. The analysis revealed that vitamin D supplementation significantly reduced thyroid-stimulating hormone (TSH) (SMD = -1.76 mIU L^- 1, 95% CI [-3.23, -0.29] mIU L^- 1), and thyroid peroxidase antibody (TPO-Ab) (SMD = -113.31 U ml^- 1, 95% CI [-141.42, -85.21] U ml^- 1). Additionally, serum vitamin D deficiency was significantly associated with the prevalence of hypothyroidism (OR = 4.06, 95% CI [1.96, 8.39]).

The results indicate that patients with hypothyroidism are more likely to have low serum vitamin D levels compared to healthy individuals. Moreover, vitamin D supplementation significantly reduced TSH and TPO-Ab levels. It is recommended that patients with hypothyroidism have serum vitamin D levels routinely monitored in clinical practice.