Low levels of physical activity can put healthy weight adults at the same risk for cardiovascular diseases as those who are overweight, a study has found.

"Our study demonstrates that a sedentary lifestyle counters the benefit of being at a normal weight when it comes to heart disease risk," said Arch G Mainous from University of Florida in the US.

"Achieving a body mass index, or BMI, in the normal range shouldn't give people a false sense of confidence they're in good health. If you're not exercising, you're not doing enough," Mainous said.

The study, published in the American Journal of Cardiology, found that 30 per cent of US adults at a normal weight are at increased risk of heart attack or stroke.

These adults had higher levels of belly fat, shortness of breath upon exertion, unhealthy waist circumference or less than recommended levels of physical activity, the researchers said.

The study focused on participants aged between 40 and 79 who did not have a previous diagnosis of coronary heart disease, stroke or heart attack.

Researchers examined participants' sagittal abdominal diameter, which is a measure of fat in the gut region, and waist circumference as well as self-reports on the amount of moderate to vigorous physical activity, the amount of time spent sitting and whether they experienced shortness of breath either when hurrying or walking up a slight hill.

In addition, researchers calculated the American College of Cardiology and the American Heart Association, or ASCVD risk score, of participants.

The ASCVD risk score uses weighted variables, including age, sex, race/ethnicity, smoking status, diabetes status, cholesterol, blood pressure and blood pressure medication status, to calculate individuals' risk of having a heart attack or stroke within the next 10 years. A score of 7.5 per cent or higher is considered high risk.