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High Frequency of and Factors Associated with Thyroid Hormone Over-Replacement and Under-Replacement in Men and Women Aged 65 and Over

Department of Medicine (L.L.S., A.R.C., N.J.) and Division of Endocrinology, Diabetes, and Metabolism (A.R.C.), University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104; Department of Biostatistics (A.M.A.), University of Washington, Seattle, Washington 98155; and Department of Epidemiology (L.P.F.), Mailman School of Public Health, Columbia University, New York, New York 10032

Address all correspondence and requests for reprints to: Anne R. Cappola, M.D., Sc.M., Division of Endocrinology, Diabetes, and Metabolism, University of Pennsylvania School of Medicine, 764 CRB, 415 Curie Boulevard, Philadelphia, Pennsylvania 19104. E-mail: acappola{at}mail.med.upenn.edu.

Context: Thyroid hormone use is common in older populations, but the frequency of over- or under-replacement is debated.

Objective: We sought to describe the frequency of and factors associated with thyroid hormone over- or under-replacement in a population of older men and women.

Design: Participants were 3678 U.S. community dwelling individuals aged 65 yr or older enrolled in the Cardiovascular Health Study who had thyroid function tests in 1989–1990. Thyroid hormone users (n = 339) were identified and classified into low TSH (<0.45 mU/liter), euthyroid (0.45–4.5 mU/liter), and high TSH (>4.5 mU/liter).

Results: Of the 339 thyroid hormone users, 41% had a low TSH, 16% had a high TSH, and 43% were in the euthyroid range. In multivariable analyses, lower weight (P < 0.001) was independently associated with low TSH status. For every 10 kg lower weight, the likelihood of having low TSH increased by 65% [odd ratio (OR) 1.65; 95% confidence interval (CI) 1.31–2.07]. Those with renal insufficiency were less likely to have low TSH levels (P = 0.02). The presence of diabetes was independently associated with having low (OR 3.35; 95% CI 1.46–7.65) and high TSH levels (OR 2.66; 95% CI 1.14–6.21).

Conclusions: There is a very high prevalence of thyroid function testing abnormalities in older people taking thyroid hormone preparations, particularly in those of low weight or with diabetes. Because of potential adverse cardiovascular and skeletal effects from over-replacement, older people represent a key population for increased TSH monitoring on therapy.