WASHINGTON, Feb. 24 -- Nearly half of adolescents born with HIV may be at increased risk of cardiovascular diseases, including heart attack and stroke later in life, according to a study released Monday by the U.S. National Institutes of Health ( NIH).

The results, published online in the journal Circulation, are based on clinical assessments of 165 teens aged 15 or older with HIV, who were born to mothers with HIV and who have been treated with anti-HIV medications since birth.

"Our results show that a large proportion of teens who have had HIV their whole lives appear to be at significant risk for cardiovascular disease later in life," said co-author George Siberry of the National Institute of Child Health and Human Development, one of the NIH institutes supporting the study. " These results indicate that individuals who have had HIV since birth should be monitored carefully by their health care providers for signs of cardiovascular disease."

Previous studies have showed that the severity of HIV infection and a history of taking specific HIV drugs are linked to cardiovascular diseases in adults.

In this study, the researchers estimated each participant's overall cardiovascular risk using a scoring system called the Pathobiological Determinants of Atherosclerosis in Youth (PDAY), which is based on measures of cholesterol levels, blood sugar level, smoking, blood pressure, and weight.

The score estimates the likelihood that a person has a build-up of artery clogging plaque in the coronary arteries or in the abdominal aorta, the main artery in the abdomen, both known to increase the risk for conditions such as heart attack and stroke.

A PDAY score of one indicates an 18 percent or 24 percent greater chance of plaque build-up in the coronary arteries or abdominal aorta, respectively, while a score of zero is thought to indicate the chances for cardiovascular disease among those of the same age and sex with no known risk factors.

Study results showed that 48 percent of the teens infected with HIV since birth had a score of one or higher for the coronary artery measure, and 24 percent scored one or above for the abdominal aorta measure. No major trends were observed in PDAY score changes over a four-year time period.

The researchers said that PDAY scores of one or higher were primarily attributable to high cholesterol levels and that patients who were treated with protease inhibitors or those with a history of AIDS were more likely to have higher PDAY scores.

The study authors called for more research to understand all the potential factors that could influence cardiovascular risk in this group.

"It's too soon to recommend changing treatment regimens on the basis of our findings," said first author Kunjal Patel of the Harvard School of Public Health. "Until we can learn more, we can best serve adolescents who have HIV by monitoring their risk factors for heart disease carefully and urging them to adopt other measures that have been found to reduce the risk of heart disease in the general population: exercising, maintaining a healthy diet, and not smoking."