People who have an underactive thyroid without symptoms appear to have an increased risk of heart disease, according to a review of published studies that appears in the American Journal of Medicine.

However, more evidence is still needed before any recommendations for screening can be made. Better studies that include more people who have had an episode of coronary heart disease will help confirm these results, lead investigator Dr. Nicolas Rodondi told Reuters Health.

Dr. Rodondi, of the University of Lausanne, Switzerland and colleagues examined data covering thousands of subjects taking part in 14 observational studies.

Overall, subjects with an underactive thyroid without symptoms, also referred to as subclinical hypothyroidism, had a 65 percent increased risk of coronary heart disease.

Nine studies included a comparison group without hypothyroidism, matched to the hypothyroid group for age and demographic factors - those with subclinical hypothyroidism had an increased risk of 81 percent for heart disease.

In studies that accounted for the potential influence of the presence of cardiovascular risk factors, the heart disease risk in subjects with subclinical hypothyroidism was more than doubled.

However, “in my opinion, the data are not good enough to recommend screening in healthy adults without any symptoms,” Rodondi added.

“Before recommending screening,” he concluded, “clinical trials are needed to assess whether thyroxine treatment reduces the risk of coronary heart disease in subjects with subclinical hypothyroidism.”

SOURCE: American Journal of Medicine, July 2006.