Thyroid status and 6-year mortality in elderly people living in a mildly iodine-deficient area: the aging in the Chianti Area Study

J Am Geriatr Soc. 2013 Jun;61(6):868-74. doi: 10.1111/jgs.12267. Epub 2013 May 6.

Abstract

Objectives: To test the hypothesis that, in older adults, living in a mildly iodine-deficient area, thyroid dysfunction may be associated with mortality independent of potential confounders.

Design: Longitudinal.

Setting: Community-based.

Participants: Nine hundred fifty-one individuals aged 65 and older.

Measurements: Plasma thyrotropin, free thyroxine, and free triiodothyronine concentrations and demographic features were evaluated in participants of the Invecchiare in Chianti Study aged 65 and older. Participants were classified according to thyroid function test. Kaplan-Meier survival and Cox proportional hazards models adjusted for confounders were used in the analysis.

Results: Eight hundred nineteen participants were euthyroid, 83 had subclinical hyperthyroidism (SHyper), and 29 had subclinical hypothyroidism (SHypo). Overt hypo- and hyperthyroidism were found in five and 15 subjects, respectively. During a median of 6 years of follow-up, 210 deaths occurred (22.1%), 98 (46.6%) of which were from cardiovascular causes. Kaplan-Meier analysis revealed higher overall mortality for SHyper (P = .04) than euthyroid subjects. After adjusting for multiple confounders, participants with SHyper (hazard ratio (HR) = 1.65, 95% confidence interval (CI) = 1.02-2.69) had significantly higher all-cause mortality than those with normal thyroid function. No significant association was found between SHyper and cardiovascular mortality. In euthyroid subjects, thyrotropin was found to be predictive of lower risk of all-cause mortality (HR = 0.76, 95% CI = 0.57-0.99).

Conclusion: SHyper is an independent risk factor for all-cause mortality in older adults. Low to normal circulating thyrotropin should be carefully monitored in elderly euthyroid individuals.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aged
  • Aged, 80 and over
  • Aging*
  • Cause of Death / trends
  • Confidence Intervals
  • Female
  • Follow-Up Studies
  • Goiter, Endemic / blood*
  • Goiter, Endemic / mortality
  • Humans
  • Iodine / blood*
  • Iodine / deficiency
  • Italy / epidemiology
  • Kaplan-Meier Estimate
  • Male
  • Proportional Hazards Models
  • Retrospective Studies
  • Risk Factors
  • Survival Rate / trends
  • Thyroid Function Tests
  • Thyroid Gland / metabolism*
  • Time Factors

Substances

  • Iodine