Age-related changes in thyroid function: a longitudinal study of a community-based cohort

Abstract

Context: In cross-sectional studies, serum TSH concentrations increase with age. This has not beenexamined longitudinally, and it is uncertain whether the TSH increase reflects healthy aging oroccult thyroid failure.Methods: We measured serum TSH, free T4, thyroid peroxidase, and thyroglobulin antibodies in1100 participants in the 1981 and 1994 Busselton Health Surveys and derived a reference group of908 individuals without thyroid disease or thyroid antibodies. We examined changes in thyroidfunction longitudinally and, in 781 participants, explored associations with the CAPZB polymorphismrs10917469.Results: At 13 yr follow-up, mean serum TSH increased from 1.49 to 1.81 mU/liter, a change in meanTSH (TSH) of 0.32 mU/liter [95% confidence interval (CI) 0.27, 0.38, P0.001], whereas mean freeT4 concentration was unchanged (16.6 vs. 16.6 pmol/liter, P 0.7). The TSH increase was mostmarked in the elderly, such that gender-adjusted TSH increased by 0.08 mU/liter (95% CI 0.04,0.11) for each decade of baseline age. People with higher baseline TSH values had proportionallysmaller increases in TSH, with each additional 1.0 mU/liter of baseline TSH associated with a 0.13mU/liter decrease (age and gender adjusted) in TSH (95% CI 0.09, 0.16). The TSH did not differsignificantly by CAPZB genotype.Conclusions: Aging is associated with increased serum TSH concentrations, with no change in freeT4 concentrations. The largest TSH increase is in people with the lowest TSH at baseline. Thissuggests that the TSH increase arises from age-related alteration in the TSH set point or reducedTSH bioactivity rather than occult thyroid disease. (J Clin Endocrinol Metab 97: 0000–0000, 2012)