Feb. 20 (HealthDay News) -- Two treatments aren't always better than one, suggests new research comparing thyroid hormone levels before and after thyroid removal surgery.

The study, published in the Feb. 20 issue of the Journal of the American Medical Association, found that when people are only given synthetic levothyroxine (T4) after thyroid removal surgery, their levels of another hormone, triiodothyronine (T3), stay about the same as they were before surgery, suggesting that treatment with additional T3 isn't necessary.

"Basically, each patient's T3 levels remained the same after surgery as it was before," said study author Dr. Jacqueline Jonklaas, an assistant professor of medicine in the division of endocrinology at Georgetown University Hospital in Washington, D.C.

As many as 27 million Americans have some type of thyroid disease, according to the American Association of Clinical Endocrinologists; about half of these people are undiagnosed.

Normally, the thyroid makes two hormones -- T3 and T4. As much as 20 percent of T3 in the blood is directly produced by the thyroid, but the rest is made in tissues outside of the thyroid that convert T4 into T3, according to Jonklaas. Most people who've had their thyroids removed or who have had thyroid tissue destroyed as a result of treatment with radioactive iodine take supplemental T4 produce adequate levels of both hormones and feel fine.

But, said Jonklaas, in a small group of people taking just T4, cognitive problems occur, and experts thought maybe it was because these people were missing the extra dose of T3 normally produced in the thyroid, rather than converted from T4.

To try to alleviate these symptoms, some physicians have prescribed combination therapy that included T4 and T3. Jonklaas said that many clinical studies have been done on the combination and that no clear benefit has been shown to prescribing T3 in addition to T4.

The addition of T3 also makes treatment and monitoring more complex. Treatment with T4 provides steady levels of both T3 and T4 hormones. However, when synthetic T3 is given, it builds up and then dissipates quickly, according to Jonklaas, who added that if patients on combination therapy aren't carefully monitored, they can develop symptoms of thyroid overactivity, such as heart palpitations and trouble sleeping.

In an attempt to put this debate to rest, Jonklaas and her colleagues followed 50 people between the ages of 18 and 65 who needed to have their thyroid removed due to thyroid nodules, cancer or a goiter. None of the volunteers had symptoms of underactive (hypo) or overactive (hyper) thyroid glands at the start of the study.

All of the study participants were treated with T4 alone after surgery.

The researchers measured T4 and T3 levels both before and after surgery and essentially found no change.

"This is further evidence that combination therapy is unlikely to be of use to people who've had thyroid surgery," said Dr. David Cooper, director of the division of endocrinology at Sinai Hospital of Baltimore and director of Johns Hopkins University's thyroid clinic. He wrote an editorial that accompanied the study.

Cooper did point out that there were some people who had slightly lower levels of T3 after surgery and that these people may be the ones who are candidates for combination therapy.

Both Jonklaas and Cooper said the findings are likely applicable to people who have improperly functioning thyroid glands as well, particularly for people with overactive thyroids that either have their thyroids removed or destroyed with radioactive iodine.

SOURCES: Jacqueline Jonklaas, M.D., Ph.D., assistant professor, medicine, division of endocrinology, Georgetown University Hospital, Washington, D.C.; David S. Cooper, M.D., director, division of endocrinology, Sinai Hospital of Baltimore, professor, medicine, Johns Hopkins University School of Medicine, director, Johns Hopkins thyroid clinic, Baltimore, and contributing editor, Journal of the American Medical Association; Feb. 20, 2008, Journal of the American Medical Association