When your body produces too-high levels of thyroid hormones, it’s called hyperthyroidism. You might feel irritable, find it hard to tolerate heat, have trouble sleeping and have a rapid heartbeat. But there’s a more subtle condition, often without symptoms, in which thyroid hormone levels tend to be “normal” but on the high side of the range. In an attempt to reduce them, your body sends out much less “thyroid stimulating hormone” (TSH). It’s called subclinical hyperthyroidism.
Until now, there’s been debate about how it can affect bone health. Now a meta-analysis of 13 studies with more than 70,000 participants has made it clear—subclinical hyperthyroidism increases the risk for fractures. Compared with people who had normal thyroid function, those with subclinical hyperthyroidism had a 28% higher overall fracture risk, including 36% higher risk for hip fracture and 51% higher risk for spine fracture. Why is fracture risk higher? One theory is that even slightly elevated thyroid hormone levels subtly tilt the balance toward bone loss. It’s a big issue, because subclinical hyperthyroidism is far from rare. If you randomly put 100 US adults in a room, three to five of them would have it. If everyone in the room were 65 years old or older, 15 would have it. Here’s what you need to know.
SHOULD YOU GET TESTED? AND TREATED?
Blood tests can diagnose the condition, and treatment usually means taking a medication that inhibits thyroid hormone. If medication fails, radiation may be considered.
There’s no harm in getting thyroid function tests, but there is substantial debate about who benefits from treatment. That’s because no clinical trials have shown that treating the condition actually reduces fracture risk. It’s a similar story with another known risk associated with the condition—atrial fibrillation, a serious heart disorder. We know that subclinical hyperthyroidism increases the risk for atrial fibrillation, but we don’t know if treating the thyroid condition reduces the risk.
Whether treatment makes sense depends not just on your thyroid function but on your age and your risk for osteoporosis as well as heart disease. A normal range for TSH is between 0.45 and 4.49 mIU/L, while subclinical hyperthyroidism is defined as having a TSH level of less than 0.45 mIU/L with thyroid hormones in the normal range. Here is the best current clinical guidance…
• If you are 65 or older and your TSH is very low (under 0.1 mIU/L), you should be treated.
• If you are 65 or older and your TSH is at least 0.1 but still low (under 0.45), talk to your doctor about treatment.
• If you are under 65 and your TSH is very low (under 0.1), talk to your doctor about treatment.
• What would tilt the scales toward treatment? If you have a cardiovascular condition or are a woman who has been through menopause and you aren’t taking hormones (which reduce osteoporosis risk), you may be a particularly strong candidate.
• If you do get tested, it’s fine to wait a few months and get tested again before jumping into treatment. Why? Because subclinical hyperthyroidism sometimes just goes away on its own.
Beware of over-the-counter thyroid supplements, too. These are marketed to help people with the opposite problem—low thyroid levels—but they often contain such high levels of thyroid hormones that they can boost you into hyperthyroidism, at least temporarily. See the Bottom Line article “Thyroid Supplements Contain Potentially Dangerous Levels of Hormones.”
Whether you are considering thyroid hormone replacement or medications to reduce thyroid hormones, do so under the careful guidance of your health-care provider. And if you’re concerned about your thyroid function affecting your heart or bones, don’t forget that we already know many effective ways to prevent heart disease and strengthen bones.