Lower thyroid activity tied to weight gain

NEW YORK (Reuters Health) - Middle-aged adults whose thyroid gland is mildly underactive, but still functioning in the normal range, may be more prone to weight gain, a new study suggests.

The thyroid is a gland in the neck that produces hormones that regulate the body's metabolism. In a disorder called hypothyroidism, the gland is underactive, causing symptoms such as fatigue, sensitivity to cold, dry skin and weight gain.

But it has been unclear whether thyroid function within the standard range has an effect on body weight.

In the current study, reported in the Archives of Internal Medicine, researchers looked at the relationship between body weight and levels of thyroid-stimulating hormone (TSH) in more than 2,400 middle-aged adults.

TSH is released by the brain to stimulate hormone production in the thyroid gland. Higher TSH levels in the blood indicate relatively lower activity in the thyroid.

In this study, men and women with relatively high, but still normal, TSH levels tended to weigh more at the outset than those with lower TSH concentrations.

Moreover, those whose TSH levels tipped upward over the next several years were more prone to weight gain.

"Our findings raise the possibility that modest increases in serum TSH concentrations within the reference range may be associated with weight gain," write the researchers, led by Dr. Caroline S. Fox of the National Heart, Lung, and Blood Institute in Bethesda, Maryland.

It's too soon, however, to start tinkering with thyroid hormones in order to treat obesity, editorialists comment.