In a new study, researchers found that thyroid hormone replacement therapy in older adults is associated with a higher risk of death compared with no treatment.
The research was conducted by a team at Johns Hopkins University in Baltimore.
When people have too little thyroid hormone, called hypothyroidism, they usually require lifelong treatment with levothyroxine to supplement the body’s thyroid hormone, thyroxine (T4).
Some people have subclinical hypothyroidism, which occurs when the thyroid gland needs more stimulation to produce adequate thyroid hormone levels.
These individuals will have modest elevations in thyroid-stimulating hormone (TSH), which stimulates thyroid hormone production.
According to the team, subclinical hypothyroidism is a mild or early form of thyroid disease, and these patients also routinely receive thyroid hormone replacement.
However, this interpretation of high TSH with normal T4 levels may not be correct in all older adults.
The researchers studied the effects of levothyroxine therapy on survival in adults ages 65 and older.
They used data from 1,054 participants of the Baltimore Longitudinal Study of Aging, a long-running observational study from the National Institute on Aging.
All participants had at least one TSH and T4 measurement since 2003.
The team looked at the risk of dying during one-year intervals from 2003 to 2018.
They found that among older adults, the use of thyroid hormone increased risk of death 60% year over year.
They also limited the analysis to compare individuals with normal TSH levels, reflecting normal thyroid function, to those on thyroid hormone with normal TSH levels, who were therefore treated to target, and found those on treatment had almost double the risk of dying compared with untreated people.
Despite studies showing that hormone treatment of an isolated high TSH may not benefit older people, the researchers were surprised that we were able to demonstrate harm associated with thyroid hormone supplementation.
The work supports the growing calls to use age-specific TSH reference intervals to determine the threshold for thyroid hormone treatment.
The team also recommended repeating testing after finding an isolated elevation of TSH in older adults, because levels can fluctuate.
The lead author of the study is Jennifer Mammen, M.D., Ph.D., an assistant professor at Johns Hopkins University in Baltimore.
The study is published in a special supplemental section of the Journal of the Endocrine Society.
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