MILWAUKEE — Paul Ryan works out and watches his diet, but a new study shows that clean living can only go so far to help people like the vice presidential candidate overcome a strong family history of heart disease.

The study of 4 million people — the largest ever on heart risks that run in families — found that having a close relative die young of cardiovascular disease doubles a person’s odds of developing it by age 50. This risk was independent of other factors like high cholesterol, high blood pressure and diabetes, and was even higher if more than one close family member had died young.

Ryan has said his father, grandfather and great-grandfather all died of heart attacks in their 50s, and the 42-year-old Wisconsin congressman has cited that as the reason for his devotion to exercise.

“I’d sure like to see him in my clinic,” said Dr. Patrick McBride, a preventive cardiology specialist at the University of Wisconsin in Madison.

Heart attacks can result from genetic factors, an abnormal heart rhythm or a heart muscle problem — not just clogged arteries from poor health habits, said McBride, who had no role in this study but has published other work on the topic.

“What’s important for anybody with that kind of story is that they sit down with their physician and get a very thorough, detailed family history and try to identify what factors may be present in the family — not just on their own think they can fix their problem,” McBride said. “Exercise alone won’t obviate this risk.”

It’s not known if Ryan has had such an evaluation, although McBride noted that as a congressman, Ryan has excellent insurance and access to care. A Mitt Romney campaign spokesman said Ryan was not available for an interview on his health, and did not answer questions about whether Ryan is taking medicines for heart risk factors such as high cholesterol or high blood pressure.

In an email message, the spokesman, Brendan Buck, said Ryan has never smoked, “works out five times a week, eats healthy, gets regular checkups, avoids sweets and limits alcohol consumption.”

The Wisconsin congressman joked “my veins run with cheese” when he was named Romney’s running mate, but it is clear that he takes the health of his arteries seriously.

Ryan’s family history of heart disease “is dramatic,” and his efforts to modify whatever risks he can control is “very wise,” said the leader of the new study, Dr. Mattis Ranthe, a scientist at the Danish Ministry of Health.

The study involved 4 million people from Denmark, which has detailed medical registries on families dating to 1949 because of universal health care.