The aging thyroid. Increased prevalence of elevated serum thyrotropin levels in the elderly.

Of 344 relatively healthy persons older than 60 years, 22 (5.9%) had a clearly elevated level of serum thyrotropin (TSH) (greater than 10 muU/mL), a finding more common in women than in men. Ten of the 22 had low values for serum thyroxine (T4) and free T4 (FT4) index, but only one had a low value for serum triiodothyronine (T3) or free T3 (FT3) index. A further 14.4% had a slightly elevated level of serum TSH (greater than 5 less than or equal to 10 muU/mL), but none had low values for serum T4 or FT4 index. Age alone has little effect on the measurements of T4; age is associated with slightly lower T3 levels, but only in men 60 years or older or in women 80 years or older. Longitudinal studies should determine if a slightly elevated serum TSH rises further with age and if there is a causal relationship between a high level of serum TSH and cardiovascular disease.