Thyroid status, disability and cognitive function, and survival in old age

CONTEXT: Despite the equivocal outcomes of randomized controlled trials, general clinical opinion favors screening and treatment of elderly individuals with subclinical thyroid disorders.

OBJECTIVES: To determine whether subclinical thyroid dysfunction should be treated in old age and the long-term impact of thyroid dysfunction on performance and survival in old age.

DESIGN, SETTING, AND PARTICIPANTS: A prospective, observational, population-based follow-up study within the Leiden 85-Plus Study of 87% of a 2-year birth cohort (1912-1914) in the municipality of Leiden, the Netherlands. A total of 599 participants were followed up from age 85 years through age 89 years (mean [SD] follow-up, 3.7 [1.4] years).

MAIN OUTCOME MEASURES: Complete thyroid status at baseline; disability in daily life, depressive symptoms, cognitive function, and mortality from age 85 years through 89 years.

RESULTS: Plasma levels of thyrotropin and free thyroxine were not associated with disability in daily life, depressive symptoms, and cognitive impairment at baseline or during follow-up. Increasing levels of thyrotropin were associated with a lower mortality rate that remained after adjustments were made for baseline disability and health status. The hazard ratio (HR) for mortality per SD increase of 2.71 mIU/L of thyrotropin was 0.77 (95% confidence interval [CI], 0.63-0.94; P = .009). The HR for mortality per SD increase of 0.21 ng/dL (2.67 pmol/L) of free thyroxine increased 1.16-fold (95% CI, 1.04-1.30; P = .009).

CONCLUSIONS: In the general population of the oldest old, elderly individuals with abnormally high levels of thyrotropin do not experience adverse effects and may have a prolonged life span. However, evidence for not treating elderly individuals can only come from a well-designed, randomized placebo-controlled clinical trial.