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Weight Gain: Thyroid Gland to Blame?

Even Low-Normal Thyroid Function Could Tip the Scales, Study Shows
By
WebMD Health News
Reviewed by Louise Chang, MD

March 24, 2008 -- If you're tempted to blame your thyroid gland for the numbers on the scale, researchers have some good news and some not-so-good news for you.

In a new study examining thyroid and weight, scientists have found that even a thyroid functioning on the lower end of the normal range is associated with weight gain.

It's long been known that a very overactive thyroid can be associated with weight loss, and a very underactive thyroid linked to weight gain. But the new research suggests that even variations within the normal range of thyroid function are associated with weight changes.

The bad news: It's too soon to know what, if anything, to do about it.

Study Details: Thyroid and Weight

The researchers evaluated the thyroid functioning of more than 2,400 men and women by looking at the results of their thyroid stimulating hormone or TSH test, a blood test to assess thyroid functioning.

"I was struck that small changes within the normal range of TSH were associated with increases in body weight," says Caroline S. Fox, MD, MPH, a study researcher and a medical officer at the National Heart, Lung, and Blood Institute's Framingham Heart Study.

The butterfly-shaped thyroid gland, located in the lower front of the neck, makes thyroid hormone, which in turn goes into the bloodstream and the rest of the body, helping it to use energy, stay warm, and function properly.

The results of the new study, published March 24 in the Archives of Internal Medicine, agree with at least two other recent studies, Fox says.

Fox and her colleagues zeroed in on 2,407 men and women who participated in the famed Framingham Heart Study -- Offspring Study, trying to find out if body weights vary within the range of normal TSH values and if changes in the TSH values over a 3.5-year follow-up affect a person's body weight.

A high TSH level reflects an underactive gland; a low TSH usually reflects hyperactivity.

The data were taken from exams done from 1983 to 1987 and 1987 to 1991. The average age at the first data collection was 48.

Results: Thyroid and Weight

"If TSH increased over time, weight was more likely to go up," Fox tells WebMD. They divided the patients into four groups, from those whose TSH increased the least to those whose TSH increased the most. "Women whose TSH changed the most gained 2.3 kilograms [about 5 pounds on average]." Some gained more.

A similar pattern was found in men, she says, although the increases were less. The men whose TSH increased the most gained on average 1.3 kilograms or nearly 3 pounds over the three-and-a-half-year follow-up.

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