Objective: Some evidence suggests that higher serum TSH may be part of normal aging, but studies are limited to a 13-year follow-up. We examined TSH changes over a 22-year follow-up across the adult lifespan.
Design: Longitudinal analyses of the population-based HUNT Study, Norway, with TSH measurements from 1995-1997, 2006-2008, and 2017-2019, and linkage to the Norwegian Prescribed Drug Registry.
Methods: In individuals without thyroid medication or overt thyroid dysfunction, we estimated (1) geometric mean serum TSH by age, integrating cross-sectional and longitudinal measurements using linear mixed models, (2) percentiles of the TSH distribution by age, and (3) within-individual TSH change during follow-up, expressed by geometric mean ratios (GMR) reflecting the fold change in geometric mean TSH.
Results: We included 127 483 TSH measurements among 80 284 participants, of whom 36 886 had ≥2 measurements and 11 749 had ∼22-year follow-up. When integrating all cross-sectional and longitudinal measurements, mean TSH was higher at older age in men, while the association with age was weaker and less consistently observed in women. When examining within-individual change, mean TSH increased modestly by 0.13 mIU/L (GMR 1.09; 95%CI 1.07, 1.10) over 22 years in men, but not in women (GMR 0.97; 95%CI 0.96, 0.98). This increase was stronger at 0.5 mIU/L in men aged ≥70 years at baseline (GMR 1.32; 95%CI 1.15, 1.48). The TSH distribution widened at older age in both sexes.
Conclusions: Mean serum TSH increased with age in older men, but showed only modest or no age-related change in younger men and in women. The wider TSH distribution at older age supports the need for age-specific TSH reference ranges.
Keywords: TSH; aging; cohort; thyroid.
© The Author(s) 2026. Published by Oxford University Press on behalf of European Society of Endocrinology.