Do Small Age-Related Rises in Thyroid-Stimulating Hormone Levels Indicate Hypothyroidism?

In cross-sectional studies, serum thyroid-stimulating hormone (TSH) levels tend to be slightly higher in older people than in younger people (JW Gen Med Jan 3 2008). This observation could indicate either the earliest stage of age-related hypothyroidism or an age-related change in the relation between free thyroxine (T₄) and TSH (i.e., an age-related change in the “set point” governing the TSH response to a given free T₄ level). To help clarify this issue, Australian researchers performed a longitudinal study of 908 people (their ages ranged from 20s to 70s at study enrollment) whose thyroid function was tested twice, 13 years apart. People with overt hypothyroidism, overt hyperthyroidism, or antithyroid antibodies were excluded.

During 13 y…