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 T4 (FT4) total T4, T3, rT3, and T4-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 rT3 increased significantly with age and the presence of disease. Sixty-three men met the biochemical criteria for the low T3 syndrome (decreased serum T3 and increased serum rT3). This was associated with a lower PPS, independent of disease. Furthermore, higher serum FT4 (within the normal range of healthy adults) and rT3 (above the normal range of healthy adults) were related with a lower grip strength and PPS, independent of age and disease. Isolated low T3 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 rT3 concentrations are associated with a lower physical function. High serum rT3 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.