Hyperthyroidism/Too Much Thyroid Hormone Increase Risk Osteoporisis

by Mary J. Shomon

April, 2001 -- According to research reported on in the April 3, 2001 issue of the Annals of Internal Medicine, older women who are taking too much thyroid replacement hormone, or who have a medical history of an overactive thyroid -- hyperthyroidism -- may face an increased risk of bone fracture.

The researchers did indicate, however, that women who were being treated with proper levels of the hormone did not face any increased bone fracturer risks.

"Too much" thyroid replacement hormone was defined as a TSH level of "less than 0.1" which is substantially hyperthyroid by most lab's ranges. The normal range at most laboratories in the United States runs from 0.5 at the low end to 5.5 at the high end. Below 0.5 is hyperthyroid, above 5.5 is considered hypothyroid.

The study followed nearly 700 women, age 65 and older, and found that women with a low TSH level (less than 0.1) had three times the risk of hip fracture and four times greater risk for vertebral fracture compared with women who had normal TSH levels (0.5 to 5.5).

The low TSH levels were associated with either taking too mjuch thyroid replacement hormone, or a hyperthyroid condition.

The study also showed that women with a history of hyperthyroidism had double the risk of hip fracture, but no increased risk of vertebral fracture.

One of the researchers, Dr. Douglas C. Bauer, associate professor of medicine at the University of California, San Francisco, told Reuters Health, "An important point is if your (thyroid level) was in the (normal) ballpark, there's been no clear evidence that thyroid hormone was bad for you."

This research is the latest in a series of research efforts that have presented conflicting findings on whether hyperthyroidism or taking too much thyroid hormone contribute to bone loss and risk of osteoporosis and bone fracture.

Last year, an article I did on the subject, [link url=http://thyroid.about.com/library/weekly/aa061100a.htm]The Thyroid Treatment/Osteoporosis Controversy[/link], presented a number of research studies that found no link between suppressive doses of thyroid hormone and increased bone loss or fracture risk, as well as other studies that, like the current one, support this theory.

Not many physicians do maintain their patients at suppressive doses such as the level described in this study. Typically, only thyroid cancer survivors -- whose TSH is suppressed to prevent cancer recurrence -- are kept at these levels. Occasionally, a physician will treat patients with suppressive doses to reduce symptoms, but this is not common. If a physician is maintaining a patient at a suppressive dose, they will typically prescribe supplemental calcium, as well as an exercise program for building and maintaining bone. For more details, read The Thyroid Treatment/Osteoporosis Controversy.

SOURCE: Annals of Internal Medicine 2001;134:561-568, 3 April 2001 Volume 134 Number 7