Ask the Doctors

Dear Doctor: I have been taking levothyroxine for an underactive thyroid for about 40 years. I have progressed from 0.025 milligrams to 100 milligrams currently. I recently read an article indicating that long-term use of this drug increases the incidence of bone fractures by about 80 percent. I am 74 years old. What alternatives are available to treat this condition?

Dear Reader: I can understand your worry about thyroid hormone and an increased risk of fractures, especially after being on the medication for 40 years. After all, people with hyperthyroidism (an excess of thyroid production) have a greater risk for osteoporosis, and studies have found that thyroid hormone increases bone resorption while interfering with calcium metabolism within the bone.

In fact, people with hyperthyroidism have a 10 to 20 percent decrease in bone density compared to people with normal thyroid levels; they also have an increased risk of fracture. A 2014 study from Denmark showed that, after 7.5 years, women with hyperthyroidism showed a fracture rate of 12.5 percent while those who had normal thyroid levels had a fracture rate of 7.6 percent. (This increased fracture rate was not seen in men.)

The impact of taking thyroid hormone to keep your levels normal is less clear. So far, it appears to depend on where in the normal range you end up. A 2017 study combined data from 13 different studies with a total of 56,835 people who took thyroid hormone replacement therapy. The studies, on average, followed people for 12 years; the average age of participants was 64, and 60 percent were women. Thyroid levels were assessed by measuring both TSH (thyroid-stimulating hormone) and T4 (the thyroid hormone thyroxine).

Now, remember: A lower TSH is associated with a higher thyroid level.

The authors found that those with the lowest range of TSH (0.45-0.99 mIU/L) had a 24 percent increased risk of hip fracture compared to those with the highest range of TSH (3.5-4.49 mIU/L). Note that both of these groups were in the normal range, but those with the higher level of thyroid hormone had a greater risk. For non-hip fractures, the association with thyroid hormone intake and fracture risk was not as great, with an 8 to 10 percent increase in risk.

The study also found that higher levels of T4 were associated with an increased risk of fractures, a finding that has been corroborated in studies in both Europe and Taiwan.

Keep in mind that the studies have been of relatively short duration, so it's difficult to know how taking thyroid hormone may have affected you specifically. I wonder, however, about your current bone density. If it's low, you should consider supplementation with calcium, vitamin D and possibly a medication to help build up bone.

Regardless, I would try to take the lowest possible dose of thyroid hormone required to keep your thyroid levels on the lower end of normal. You should also make sure you walk and do weight-bearing exercises to help decrease your risk of osteoporosis.

As for supplements or lifestyle changes that promise to naturally boost thyroid hormone production, these are not reliable options. Nor will they reduce the risk for fractures. Stick with medications proven to work -- and at the lowest possible level.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

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