Low thyroid function may worsen heart risk: study

WASHINGTON (Reuters) - Women with slightly low thyroid function may have a higher risk of death from heart disease, Norwegian researchers reported on Monday.

Even women whose thyroid function was considered clinically normal, but at the low end of the range, were more likely to die of heart disease, the researchers found.

They said doctors should take seriously readings of thyroid hormone levels and recommended more studies to see if treating low thyroid function reduces the risk of heart disease.

Thyroid function is measured indirectly, by looking at a hormone called thyrotropin, or thyroid stimulating hormone -- TSH for short.

Another gland, the pituitary gland, releases TSH, and high TSH levels can indicate low thyroid function. This can cause symptoms such as sluggishness, hair loss, weight gain and a feeling of being cold.

Clinically low thyroid function is seen in an estimated 10 percent of older women, who can take a daily thyroid hormone pill to correct it.

Dr. Bjorn Asvold of the Norwegian University of Science and Technology in Trondheim and colleagues studied 17,311 women and 8,002 men without known thyroid disease, cardiovascular disease or diabetes at the beginning of the study.

Over the next eight years, 1.3 percent of the women and 2.3 percent of the men died of heart disease.

The higher the TSH levels, indicating low thyroid function, the higher the risk of heart death. The link was not significant in men but it was significant in women, Asvold reported in the Archives of Internal Medicine.

And it was true even for levels that had been considered normal and healthy, they said.

"This study shows that coronary heart disease mortality increases in women with increasing levels of thyrotropin within the reference range," they wrote.

"These results indicate that relatively low but clinically normal thyroid function may increase the risk of fatal coronary heart disease."

Thyroid hormones may affect the heart and arteries in several different ways, the researchers said -- they affect heart and blood vessel muscle cells, cholesterol and other functions.

They said no one appears to have tested whether replacing thyroid hormone might affect heart disease risk, although patients who get replacement thyroid hormones do lose weight, show improved cholesterol levels and see improvements in artery health.

(Reporting by Maggie Fox)