If you have a relative who died of heart disease before age 60, your own risk of early heart trouble is higher as well, a study involving millions of people in Denmark over three decades has determined.

Family history of premature heart disease has long been considered a risk factor for heart problems in future generations, and the new study, which appeared in the Journal of the American College of Cardiology, strengthens this evidence.

Researchers found that people with a parent or sibling who died young of heart problems were roughly twice as likely as others to be diagnosed with coronary heart disease - where "plaques" build up in the heart arteries, raising the risk of heart attack before age 50.

They also had double the risk of suffering a ventricular arrhythmia, an often fatal rhythm disturbance in the heart's main pumping chamber.

"As with other chronic diseases, people should try to find out what they can about their family history," said Mattis Flyvholm Ranthe, the lead researcher on the study, in an email.

Researchers at the Statens Serum Institut in Copenhagen combed through public health data on almost four million Danish citizens born after 1949.

Between 1978 and 2008, almost 130,000 of them were diagnosed with some form of cardiovascular disease before age 50. Those odds were heightened when a first-degree relative had died of heart problems before hitting 60.

But those risks also were elevated when a second-degree relative, such as a grandparent or half-sibling, had died young. The risk of coronary disease, for example, was 43 percent higher in people with one second-degree relative who had died before age 60.

"This study tells us that a grandparent's history is meaningful too," said Amit Khera, who directs the preventative cardiology program at the University of Texas Southwestern Medical Center in Dallas.

The more relatives who died young, the greater the risk. When two or more first-degree relatives died of heart problems before age 60, a person's own risk of early heart disease rose five-fold.

It's not fully clear how much of a difference that lifestyle changes or medication for high blood pressure or cholesterol can make for people with heart disease in their family, but it's known that those steps help curb heart risk in general.

"There's no reason to suspect that preventive measures wouldn't apply to these folks as well," Khera said.

The study is published in the Journal of the American College of Cardiology.