People who use over-the-counter "thyroid（甲状腺） support'' supplements may be putting their health at risk, according to a study being presented at the annual meeting of the American Thyroid Association. The supplements contain varying amounts of two different kinds of thyroid hormones apparently derived in large part from chopped up animal thyroid glands, says the study's senior investigator, Victor Bernet, M.D., an endocrinologist（内分泌学家） at Mayo Clinic in Florida. The hormones are known as T3, or triiodothyronine, and T4, or thyroxine. They are regulated by the U.S. Food and Drug Administration and intended for use only in prescription medication because they can cause significant health issues, such as an increase in heart rate, heart irregularities and palpitations（心悸） , nervousness, and diarrhea（腹泻） , Dr. Bernet says.

"These hormones have effects throughout the body, which is why they are controlled," he says.

Not only did nine of the 10 supplements studied have animal hormone, the amount of hormones in the products varied significantly, sometimes exceeding doses used for individual patients and comparable to levels found in prescription thyroid medication, Dr. Bernet says.

The supplements likely do not give most people the results they are seeking, such as weight loss or less fatigue, he says.

"The amount of thyroid hormone a normal person would have to take to lose weight would be dangerously high and there is no evidence that use of thyroid hormone effectively treats fatigue when used in people without actual hypothyroidism（甲状腺功能减退） ," he says.

Because physicians have seen a number of abnormal thyroid tests from patients using over-the-counter supplements, Dr. Bernet became interested in this issue when he heard reports of such cases as chairman of the American Thyroid Association's public health committee. He worked with researchers including endocrinologists at Walter Reed Army Medical Center, where he practiced at the time.

The researchers bought 10 commercially available thyroid supplements from stores or websites and used high-pressure liquid chromatography to separate and identify the chemical components of T3 and T4. Nine of the 10 contained T3 and five of them would deliver as much, or more, than 50 percent of the total amount of T3 produced by the body daily.

Four of the 10 supplements contained T4, and some of those contained a dose that could be twice as much as what an adult needs each day. Only one supplement had no detectable T3 or T4.

The results show there is a need for more effective monitoring of the contents of over-the-counter thyroid support products and more patient education about the products' potential health risks, Dr. Bernet says.

The study was funded by the Department of Clinical Investigation at Walter Reed Army Medical Center, which, in August 2011, became the Walter Reed National Military Medical Center.