Increased serum thyroid-stimulating hormone (TSH) and normal free thyroxine (fT4) concentration is diagnostic of subclinical hypothyroidism. Age and population-specific reference intervals are therefore critically important. Previous reports indicate that serum TSH concentrations and distribution gradually increase with age. This paper examined the TSH concentrations in a population of Ashkenazi Jews with exceptional longevity. The study population consisted of 232 Ashkenazi Jewish centenarians (median age 98 y). Younger Ashkenazi Jews were recruited as a control group (n = 188, median age 71 y), along with a second control group (n = 605, median age 68 y) from the NHANES 1998–2002 data, which were used to exclude the possibility of an ethnicity-related bias.

Serum TSH (Immulite 2000) was significantly higher in the centenarians compared with the Ashkenazi controls, with a TSH distribution shifted to significantly higher concentrations. Serum fT4 concentrations were similar in the centenarians and Ashkenazi control group, with an inverse correlation between fT4 and TSH in both groups. Median TSH concentrations were similar in the Ashkenazi and NHANES control groups, with no significant difference in TSH distribution.

Previous studies have shown a progressive increase in median TSH concentration in the ageing population. This study demonstrates that this increase continues in individuals with extreme longevity. The authors discuss possible causes for this, including medications, age-related changes in TSH glycosylation, atrophic thyroid changes, alteration of the TSH set-point or autoimmune hypothyroidism. The inverse relationship between fT4 and TSH observed supports the latter of these two possibilities. The authors posit that the TSH and fT4 concentrations seen in the centenarians may have been present from a young age and contribute to healthy ageing, although autoimmune thyroid disease (also known to increase in prevalence with age) may contribute. The authors advise against routinely prescribing levothyroxine to elderly patients with minimally increased TSH.