Thyroid Hormone Supplementation and All-Cause Mortality in Community-Dwelling Older Adults: Results from the Baltimore Longitudinal Study of Aging

Background: Although elevated thyrotropin (TSH) is common in older adults, controversy exists over what degree of elevation should be treated with thyroid hormone supplements. Isolated, elevated TSH in this population can be consistent with aging-related adaptations rather than indicative of primary thyroid disease, raising the possibility that thyroid hormone replacement may be harmful. Objectives: Determine the association between all-cause mortality and levothyroxine use among older adults. Design: Longitudinal observational study. Setting: Baltimore Longitudinal Study of Aging. Participants: One thousand two hundred and fifty eight community dwelling adult participants aged 65+ with an average of 9 years of follow up. Measurements: Thyroid and pituitary hormone levels and thyroid hormone supplementation were determined at each visit. Incident rate ratios (IRR) for all-cause mortality were calculated using time-dependent Poisson regression models to accommodate the varying start times. To isolate the effects of hormone replacement from its effects on TSH, the association between treatment and all-cause mortality was analyzed in participants with stable thyroid function status throughout follow-up (N = 638). Results: Thyroid hormone supplementation was not associated with a significant increase all-cause mortality in the subsequent year in the fully adjusted model (IRR = 1.40, 95% confidence interval (CI) = 0.93–2.12). In a stratified analysis of euthyroid participants, thyroid hormone use was associated with significantly greater mortality, with an adjusted IRR = 1.81 (95% CI = 1.10–2.98). Conclusion: The increased mortality associated with thyroid hormone use among the subclass of euthyroid community dwelling older adults is consistent with a model in which TSH elevation can result from a variety of underlying pathophysiologic processes, not all of which should be treated with thyroid hormone supplementation. Clinicians should consider overall clinical status when interpreting an isolated elevated TSH in older adults.