Hypothyroidism, lower FT4 levels tied to greater T2D risk

People with hypothyroidism and lower free thyroxine (FT4) levels in the reference range have a higher risk of type 2 diabetes (T2D), suggests a recent study.

In this systematic review and meta-analysis, the authors combined the evidence from prospective studies addressing the association between thyroid function and T2D. They searched the databases of Embase, Medline, Web of Science, Cochrane, and Google Scholar for relevant studies.

Two independent reviewers extracted data using a standardized protocol. The authors evaluated the quality of studies using the Newcastle-Ottawa Scale and calculated the pooled hazard ratios (HRs) and 95 percent confidence intervals (CIs) using random-effects models.

Out of 4,574 publications identified, only seven met the eligibility criteria and were included in the qualitative synthesis. Of these, six were included in the meta-analysis. Studies examined hypothyroidism (n=6), hyperthyroidism (n=5), thyrotropin (TSH) in the reference range (n=4), and FT4 in the reference range (n=3) in relation to incident T2D.

The pooled HR for T2D risk was 1.26 (95 percent CI, 1.05‒1.52) for hypothyroidism, 1.16 (95 percent CI, 0.90‒1.49) for hyperthyroidism, 1.06 (95 percent CI, 0.96‒1.17) for TSH in the reference range, and 0.95 (95 percent CI, 0.91‒0.98) for FT4 in the reference range.

“Further population-based studies are needed to address this association given the limited evidence,” the authors said.

“Thyroid hormones are important regulators of glucose metabolism, and studies investigating the association between thyroid function and T2D incidence have shown conflicting results,” they noted.