High-Normal Thyroid Function and Its Impact on Longevity in Men

Serum free T4 (FT4) is an independent predictor of adverse health outcomes and mortality risk in older men, according to findings of a study from Sweden published in the Journal of the Endocrine Society.1

The prospective, population-based study was conducted to examine if serum free thyroxine (FT4) or thyroid-stimulating hormone (TSH) could predict mortality, cardiovascular disease (CVD), or cancer risk in older men. A total of 1801 Swedish men, mean age 75 years, from the Gothenburg and Malmö sub cohorts of the prospective, population-based Osteoporotic Fractures in Men Study-Sweden (MrOS-Sweden) study were followed for a median of 12.2 years for all-cause mortality and 5.1 years for incident CVD and cancer. During follow-up, 338 participants developed incident CVD, and 249 developed cancer; 1207 (67%) deaths occurred. Eligibility criteria were limited to men who could walk unaided, self-report information, and provide informed consent.

High levels of FT4, per one standard deviation (SD) increase, showed a significant association with increased all-cause mortality [hazard ratio (HR) 1.23] and incident CVD events (HR 1.25). No such association was noted for risk of cancer. Of note, the association between FT4 and CVD was driven mainly by cerebrovascular events (HR 1.56). Serum TSH showed no association with mortality, CVD, or cancer risk.

This study demonstrates an association between raised FT4, and higher mortality and cerebrovascular risk. Analyses was performed both in the overall cohort and specifically in men with normal serum TSH levels. Hence, it would be more prudent to monitor FT4 levels in older men rather than relying on TSH for cardiovascular risk stratification. The authors also state,“…if FT4 levels are measured early, preventive actions can be initialized to minimize the risk of mortality and CVD events”.

Source:   Svensson J, et al. Higher serum free T4 is associated with increased risk of mortality and cerebrovascular events in elderly men. J Endocr Soc. 2025 Jul 18;9(9):bvaf121. doi: 10.1210/jendso/bvaf121.