Thyroid function and all-cause mortality in the context of multimorbidity: results from two population-based studies.

Abstract

Background: Thyroid dysfunction is common in aging populations and associated with increased non-communicable disease risk. Complex disease interactions in multimorbidity may influence this association. We aimed to examine the association between thyroid function and all-cause mortality in the context of multimorbidity.

Methods: We included participants with thyroid function measurements and recorded disease status from the PREVEND and the Rotterdam studies and categorized them into three groups (no disease, one disease and multimorbidity). We utilized cox-proportional hazards models for the associations between thyroid function and all-cause mortality. Hazard ratios (HRs) were expressed per one unit increment in thyroid function Z-scores.

Results: 5537 participants (mean age 53.0 years) from PREVEND and 9080 participants (mean age 64.9 years) from the Rotterdam Study were included. Higher FT4 concentrations were associated with a higher all-cause mortality risk in the Rotterdam Study, with HRs per 1 unit increase in Z-score of 1.07 (1.03-1.12), 1.09 (1.04-1.15), 1.21 (1.11-1.31) for individuals with no disease, one disease, and multimorbidity respectively (p for trend<0.001), while a similar but non-significant trend was observed in PREVEND. We show a lower mortality risk for higher FT3 concentrations among individuals with one disease (HR per 1 unit increase in Z-sore: 0.82, 0.70-0.97) and multimorbidity (HR 0.80, 0.61-1.05) (p for trend=0.002).

Conclusion: We show an association between higher FT4 and mortality for individuals with multimorbidity, while lower FT3 was associated with poor survival in individuals with multimorbidity. Our results extend findings from patient populations to people with multimorbidity from the general population. Future research is needed to investigate whether these findings extend to levothyroxine users.