Folate concentrations in thyroid disorders: a systematic review and meta-analysis

Nutritional factors, including folate, may modulate thyroid function; however, evidence comparing folate concentrations in adults with thyroid disorders (TD) and healthy individuals remains inconsistent. This systematic review and meta-analysis (PROSPERO registration number: CRD420251087038) synthesized evidence on differences in serum folate concentrations between these groups. Multiple databases were systematically searched without restrictions to identify observational studies comparing serum folate concentrations between adults with hypothyroidism, subclinical hypothyroidism (SH), autoimmune thyroid disease (AITD), or hyperthyroidism and healthy controls. Random-effects metanalyses were performed, with the standardized mean difference (SMD) as the effect measure. Overall, 28 studies ( n = 5492 participants) were included. No significant differences in serum folate concentrations were observed between healthy controls and patients with hypothyroidism (SMD: −0.73; 95% CI: −1.48 to 0.02; P > .05), SH (SMD: −0.35; 95% CI: −1.05 to 0.35; P > .05), AITD (SMD: 0.04; 95% CI: −0.37 to 0.29; P > .05), and hyperthyroidism (SMD: 0.79; 95% CI: −0.17 to 1.74; P > .05). No statistically significant differences were observed in serum folate concentrations between adults with TD (hypothyroidism, SH, AITD, and hyperthyroidism) and healthy controls.