Older adults may be taking “excessive” doses of thyroid medication that puts them at increased risk of fractures, Canadian researchers have found.
Hypothyroidism – an underactive thyroid gland – is more common in women than men. Symptoms include fatigue, weight gain, sluggish bowels and slower mental functioning. Patients are typically diagnosed in early or middle adulthood using a blood test, and prescribed levothyroxine
Although the need for the medication diminishes with age, prescribed doses often remain unchanged, according to a study published in the British Medical Journal.
“Our concern is that some people are getting perhaps a little bit too much,” says the study’s senior author, Lorraine Lipscombe
Using population-based data from Ontario, the study included 213,511 patients aged 70 and up with at least one prescription for thyroid medication dispensed over a five-year period. About 90 per cent were women.
Overall, the rate of fractures among patients was 10.4 per cent over the five years. But compared with patients on low-dose levothyroxine, patients on high and medium doses of the drug had a “significantly higher risk of fractures,” researchers concluded.
High doses of levothyroxine were associated with a 3.5-fold higher risk of fractures while the medium-dose group had a 2.5-fold higher risk.
The risk of bone breaks, including hip fractures, was higher even after accounting for other risk factors, such as osteoporosis, poor kidney function, other medications and previous fractures, Dr. Lipscombe says.
“The levothyroxine had a much stronger effect than any of these other things,” she says. “I think more research needs to be done to determine whether maybe in older people, the targets [for dosage] should be different.”
The age at which requirements for levothyroxine drop may vary, depending on decreasing kidney function and other age-related changes. And at menopause, women need less thyroid hormone because of changes in estrogen levels, Dr. Lipscombe says.
The study suggests that dosage should be adjusted and monitored over time, she says. “I think what’s under recognized is that as we age, we do need to keep on top of it.”
If dosage does not match the patient’s actual needs, elevated levels of the synthetic hormone may lead to lower bone density. As well, the medication may reduce muscle strength and increase the chances of falls, earlier research suggests.
Dr. Lipscombe recommends that older patients being treated for hypothyroidism ask a doctor about taking a blood test to see if they’re on the right dose. But she cautions against going off thyroid medication altogether because that could lead to weight gain, fatigue and other problems, she says.
