Objective:

To examine the association between thyroid function and all-cause mortality, particularly emphasizing the role of multimorbidity.

Key Findings:

• Higher free T4 concentrations were associated with increased all-cause mortality risk in the Rotterdam Study (HR per 1-unit increase in Z-score: 1.07 for no disease, 1.09 for 1 disease, 1.21 for multimorbidity).
• Lower free T3 concentrations were linked to poorer survival in individuals with 1 disease (HR: 0.82) and multimorbidity (HR: 0.80).
• The association between thyroid function and mortality varied significantly based on the presence of multimorbidity.

Interpretation:

The findings suggest that thyroid function impacts mortality risk differently depending on the presence of multimorbidity, highlighting the need for tailored approaches in managing thyroid dysfunction in older populations, particularly in clinical settings.

Limitations:

• The study excluded participants taking thyroid medications and those with thyroid diseases, which may limit generalizability to the broader population.
• The observational nature of the study does not establish causation, which should be considered when interpreting the results.

Conclusion:

The study extends previous findings on thyroid function and mortality to a general population context, indicating the need for further research, especially regarding levothyroxine users, to inform public health strategies.