OR11-6 Thyroid Function Testing in Older Adults Taking Levothyroxine and Risk of Adverse Outcomes

Program: Abstracts - Orals, Poster Previews, and Posters
Session: OR11-Thyroid Hormone Action, Cancer and Clinical Thyroid
Friday, April 1, 2016: 11:45 AM-1:15 PM
Presentation Start Time: 1:00 PM
Room 109 (BCEC)

Outstanding Abstract Award
Paige Meizlik*1, Alice Arnold2, Michelle Carlson3, John Robbins4, Bruce Psaty2 and Anne R Cappola5
1Hospital of the University of Pennsylvania, Philadelphia, PA, 2University of Washington, Seattle, WA, 3Johns Hopkins University, Baltimore, MD, 4UC Davis Health System, Sacramento, CA, 5Perelman School of Medicine at the University of Pennsylvania, Philadelphia, PA
Background:Thyroid hormone use is common in older people, and overreplacement occurs frequently. Endogenous subclinical hyperthyroidism is associated with increased risk of fracture and atrial fibrillation. However, at similar TSH concentrations, T4 levels are higher and T3 levels are lower in levothyroxine users, and extrapolation of findings from untreated endogenous thyroid dysfunction to thyroid hormone use may not be appropriate. We sought to determine the relationship between thyroid function and adverse outcomes in older adults taking levothyroxine.

Methods:We examined associations between TSH (mIU/L), free T4 (pmol/L), and total T3 (nmol/L) and incidence of hip fracture, atrial fibrillation, dementia, coronary heart disease (CHD), heart failure, and total mortality in 360 US community-dwelling men and women aged 65 years and over who were enrolled in the Cardiovascular Health Study and taking levothyroxine. Cox proportional hazard models were used to examine the relationship between each thyroid test and incident events; TSH was log-transformed. All models were adjusted for age, sex, race, and outcome specific covariates.

Results:Mean age was 74.8 years and 79% were women. Only 51% of these levothyroxine users were euthyroid; 13% had overt hyperthyroidism, 16% had subclinical hyperthyroidism, and 20% had an elevated TSH.  There were 28 cases of incident hip fracture. Higher TSH levels were associated with a lower risk of hip fracture (HR 0.84; 95% CI 0.71-0.98, p=0.03 for lnTSH) and, concordantly, higher free T4 levels were associated with a higher risk of hip fracture (HR 2.63, 95% CI 1.26-5.50, p=0.01). There were 31 cases of incident dementia and 57 cases of incident CHD. Higher free T4 levels were associated with a higher risk of dementia (HR 2.57, 95% CI 1.18-5.56), p=0.02) and a lower risk of CHD (HR 0.42, 95% CI 0.19-0.93, p=0.03). There were 57 cases of incident atrial fibrillation and 70 cases of incident heart failure. There were no associations between any thyroid function test and atrial fibrillation or heart failure. There were 122 deaths. Higher total T3 levels were associated with lower risk of mortality (HR 0.35, 95% CI 0.19-0.64, p=0.001), consistent with nonthyroidal illness syndrome.

Conclusions: Higher free T4 concentrations are associated with a higher risk of hip fracture and dementia, and a lower risk of CHD, in older levothyroxine users. Clinical trials are needed to evaluate the optimal target concentrations for thyroid hormone replacement in older people.

Nothing to Disclose: PM, AA, MC, JR, BP, ARC

*Please take note of The Endocrine Society's News Embargo Policy at https://www.endocrine.org/news-room/endo-annual-meeting/pr-resources-for-endo

Sources of Research Support: The research reported in this article was supported by R01AG032317 and K24AG042765 from the National Institute on Aging, contracts HHSN268201200036C, HHSN268200800007C, N01 HC55222, N01HC85079, N01HC85080, N01HC85081, N01HC85082, N01HC85083, N01HC85086, and grant HL080295 from the National Heart, Lung, and Blood Institute, with additional contribution from the National Institute of Neurological Disorders and Stroke. Additional support was provided by AG023629 from the National Institute on Aging.