People who have an underactive or overactive thyroid without symptoms appear to have a modestly increased risk of heart disease.

The data suggest that silent or “subclinical” thyroid dysfunction “might represent a potentially modifiable - albeit modest - risk factor for coronary heart disease and mortality,” Dr. Nicholas Rodondi, from the University of Lausanne in Switzerland, and colleagues wrote in a report.

Their findings are based on pooled data from 12 studies identified through a search of MEDLINE (1950 to 2008). Ten of the studies involved population-based groups that included 14,449 subjects.

All of the population-based studies examined the impact of subclinical hypothyroidism on heart disease and mortality, whereas only five looked at the effect of subclinical hyperthyroidism, the report indicates.

The likelihood of coronary heart disease, heart-related death, and death from any cause was higher by 20 percent, 18 percent, and 12 percent, respectively, in subjects with an underactive thyroid without symptoms - also referred to as subclinical hypothyroidism.

People with an overactive thyroid but without symptoms (i.e., silent hyperthyroidism) had a 21 percent, 19 percent, and 12 percent greater odds, respectively, of heart disease, heart-related death, and death from any cause.

Rodondi and colleagues say studies are needed to determine the impact of treating these two conditions on heart disease risk.

SOURCE: Annals of Internal Medicine, online May 20.