Thyroid hormone concentrations, disease, physical function, and mortality in elderly men

Context: Physiological changes in thyroid hormone concentrations might be related to changes in the overall physical function in the elderly. Objective: We determined to what extent thyroid hormone concentrations are related to physical function and mortality in elderly men. Design: A longitudinal population study (the Zoetermeer study) was conducted. Mortality was registered in the subsequent 4 yr. Participants: Four hundred three independently and ambulatory living men (aged 73-94 yr) participated. Main Outcome Measures: The study examined the association between serum thyroid hormones and parameters of physical function as well as the association with mortality. Methods: TSH, free T-4 (FT4) total T-4, T-3, rT(3), and T-4-binding globulin were measured. Physical function was estimated by the number of problems in activities of daily living, a measure of physical performance score (PPS), leg extensor strength and grip strength, bone density, and body composition. Results: Serum rT(3) increased significantly with age and the presence of disease. Sixty-three men met the biochemical criteria for the low T-3 syndrome (decreased serum T-3 and increased serum rT(3)). This was associated with a lower PPS, independent of disease. Furthermore, higher serum FT4 (within the normal range of healthy adults) and rT(3) (above the normal range of healthy adults) were related with a lower grip strength and PPS, independent of age and disease. Isolated low T-3 was associated with a better PPS and a higher lean body mass. Low FT4 was related to a decreased risk of 4-yr mortality. Conclusions: In a population of independently living elderly men, higher FT4 and rT(3) concentrations are associated with a lower physical function. High serum rT(3) may result from a decreased peripheral metabolism of thyroid hormones due to the aging process itself and/or disease and may reflect a catabolic state. Low serum FT4 is associated with a better 4-yr survival; this may reflect an adaptive mechanism to prevent excessive catabolism.