Serum 25-hydroxyvitamin D levels are associated with thyroid diseases: A systematic review and meta-analysis

Vitamin D, an important immunomodulator, has been implicated in the pathogenesis of thyroid disease. Although several studies have reported lower serum vitamin D levels in patients with autoimmune thyroid diseases (AITDS) and thyroid cancer, others have yielded shown inconsistent findings, leaving the clinical significance of vitamin D status in thyroid diseases unclear. This review aimed to clarify the association between serum vitamin D levels and thyroid diseases.

Observational studies, investigating the association between serum vitamin D levels and thyroid diseases, were identified through systematic searches of the PubMed, EMBASE, Web of Science, OVID, and Cochrane Library databases, with the search last updated in March 2024. Two reviewers independently screened the identified studies, extracted relevant data, and assessed study quality using the Newcastle-Ottawa Scale. Weighted mean differences (WMDs) with 95% confidence intervals (CIs) were calculated using a random-effects model. Statistical heterogeneity was assessed using the I2 statistic, and subgroup and sensitivity analyses were performed.

A total of 38 studies were included in the systematic searches. Serum vitamin D levels were significantly lower in patients with thyroid diseases than in the non-thyroid disease controls (WMD -5.42 ng/mL; 95% CI, -6.61--4.67; P < .001), especially in AITDs (Graves' disease ([WMD = -4.11 ng/mL, 95% CI: -7.37--0.85], Hashimoto's thyroiditis [WMD = -7.53 ng/mL, 95% CI: -11.27--3.8], and unclassified autoimmune thyroid disease (AITD) [WMD = -2.23 ng/mL, 95% CI: -3.25--1.21]).

Patients with thyroid disease had significantly lower vitamin D levels than individuals without thyroid diseases, and a more pronounced association was observed among patients with AITDs.