title: Age-related changes in thyroid function: a longitudinal study of a community-based cohort.
abstract: BACKGROUND
  In cross-sectional studies, serum TSH concentrations increase with age. This has not been examined longitudinally, and it is uncertain whether the TSH increase reflects healthy aging or occult thyroid failure.
  
  
  METHODS
  We measured serum TSH, free T(4), thyroid peroxidase, and thyroglobulin antibodies in 1100 participants in the 1981 and 1994 Busselton Health Surveys and derived a reference group of 908 individuals without thyroid disease or thyroid antibodies. We examined changes in thyroid function longitudinally and, in 781 participants, explored associations with the CAPZB polymorphism rs10917469.
  
  
  RESULTS
  At 13 yr follow-up, mean serum TSH increased from 1.49 to 1.81 mU/liter, a change in mean TSH (ΔTSH) of 0.32 mU/liter [95% confidence interval (CI) 0.27, 0.38, P < 0.001], whereas mean free T(4) concentration was unchanged (16.6 vs. 16.6 pmol/liter, P = 0.7). The TSH increase was most marked in the elderly, such that gender-adjusted ΔTSH 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 proportionally smaller increases in TSH, with each additional 1.0 mU/liter of baseline TSH associated with a 0.13 mU/liter decrease (age and gender adjusted) in ΔTSH (95% CI 0.09, 0.16). The ΔTSH did not differ significantly by CAPZB genotype.
  
  
  CONCLUSIONS
  Aging is associated with increased serum TSH concentrations, with no change in free T(4) concentrations. The largest TSH increase is in people with the lowest TSH at baseline. This suggests that the TSH increase arises from age-related alteration in the TSH set point or reduced TSH bioactivity rather than occult thyroid disease.
authors.affiliation: School of Population Health, The University of Western Australia, Nedlands, Western Australia 6009, Australia.
authors.forename: Alexandra P
authors.initials: AP
authors.lastname: Bremner
authors.forename: Peter
authors.initials: P
authors.lastname: Feddema
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Leedman
authors.forename: Suzanne J
authors.initials: SJ
authors.lastname: Brown
authors.forename: John P
authors.initials: JP
authors.lastname: Beilby
authors.forename: Ee Mun
authors.initials: EM
authors.lastname: Lim
authors.forename: Scott G
authors.initials: SG
authors.lastname: Wilson
authors.forename: Peter C
authors.initials: PC
authors.lastname: O'Leary
authors.forename: John P
authors.initials: JP
authors.lastname: Walsh
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D001323:Autoantibodies / Q000097:blood; D003430:Cross-Sectional Studies; D005260:Female; D006306:Health Surveys; D006801:Humans; D007453:Iodide Peroxidase / Q000097:blood; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D013954:Thyroglobulin / Q000276:immunology; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000502:physiology*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood
chemical_list: D001323:Autoantibodies; C006606:anti-thyroglobulin; D013972:Thyrotropin; D013954:Thyroglobulin; D007453:Iodide Peroxidase; D013974:Thyroxine