What do thyroid function profiles look like in older adults?
Interpreting data from studies done in elderly subjects regarding thyroid function is difficult because evaluation is often complicated by the increased prevalence of chronic diseases and medication use. Nevertheless, serum TSH concentrations and distributions appear to increase with age, independent of the presence of antithyroid antibodies. This has been hypothesized to be caused by an age-related decline in thyroid function or to recalibration of the baseline TSH setpoint; however serum free thyroxine (fT 4 ) levels tend to remain stable with age. Older individuals with higher fT 4 levels have been reported to have a lower physical function status and an increase in overall 4-year mortality. Total triiodothyronine (T 3 ) levels have been shown to be inversely related to physical performance and lean body mass. Serum reverse T 3 (rT3) levels appear to increase with age, presence of disease, and lower physical function status. These trends in thyroid hormone levels may indicate that it is beneficial to have lower activity of the thyroid hormone axis in older age.
Establishment and widespread use of age-specific reference ranges have been proposed and would have important implications for defining subclinical hypothyroidism in the elderly and treatment targets for thyroid hormone replacement.