People at genetic risk for heart disease can decrease chances of heart attack by getting active A new study examines how physical activity can help reduce heart health risks.

If you have a parent or sibling with heart disease, especially one that died at a young age, should you avoid exercise because of your genetic risk?

A new study says, quite clearly, no.

Many people likely know that staying active and physically fit, in addition to other healthy behaviors, can prevent heart disease.

Heart disease is the number one cause of death of men and women in the United States -- it kills more than 700,000 people yearly. Heart attacks, heart failure, stroke and abnormal heart rhythms such as atrial fibrillation are all under the “heart disease” umbrella, and most of these conditions involve narrowed or blocked blood vessels.

A new study published in the American Heart Journal, Circulation, looked at almost 5 million men and women of different ages and races in Europe and followed them over the course of about six years.

All were at risk for heart disease due to genetics but had other risk factors as well -- from high blood pressure and diabetes to high cholesterol and smoking. Researchers measured fitness and physical activity of the study's participants through a survey, and by fitness monitors, such as a Fitbit.

People in the study were deemed as a high, moderate or low risk for heart disease based on their family history.

The results were surprising. The most active people -- even considering their other high-risk factors -- saw their risk of having a heart attack, stroke or atrial fibrillation drop by almost 50 percent. This was true of those with even a low or moderate genetic risk for heart disease.

Every year, one in every six U.S. healthcare dollars will be spent on cardiovascular disease, and that dollar number will be expected to rise to approximately $818 billion by 2030, according to the Centers for Disease Control and Prevention (CDC).

However, exercise is the most cost-effective way to help prevent heart disease.

There is no magic number of minutes of weekly exercise that doctors can recommend to make a difference, but the American Heart Association currently recommends 40 minutes of moderate to vigorous intensity exercise three to four times per week to prevent a heart attack or stroke. So to maintain a healthy heart despite those bad genes -- avoid smoking, eat a heart-healthy diet and push activity levels up to get that risk down.

Dr. Roshini Malaney is a cardiology fellow at Stony Brook University Hospital working with the ABC News Medical Unit.