Married partners don't just have a lower risk of heart problems, the researchers said. They also have a lower risk of cardiovascular disease affecting the legs, neck or abdominal areas.
"We found that being married was associated with lower risks of cardiovascular disease in general," said study researcher Dr. Carlos Alviar, a cardiology fellow at NYU Langone Medical Center in New York City.
Alviar is scheduled to present the findings Saturday at the annual meeting of the American College of Cardiology, in Washington, D.C.
Although several other studies have found that marriage helps the heart and overall health, this newest one is believed to be the largest, Alviar said. And although some other studies have found the benefit greater for married men than for married women, this study did not find gender differences, he said.
For the new study, the researchers analyzed records from a database of more than 3.5 million people nationwide. All had been evaluated for cardiovascular disease, including heart disease and vascular problems in the limbs and other areas. The database included information on whether they had high blood pressure or diabetes, were smokers or were obese -- all risk factors for heart disease.
The participants' ages ranged from 21 to 102, and the average age was 64. Of all the people studied, 69 percent were married, 14 percent were widowed, 9 percent were divorced and 8 percent were single. The singles were considered the comparison group.
Even after taking into account risk factors such as age, gender and race, marriage was still protective, researchers found.
"Married men and women had 5 percent lower odds of any vascular disease," Alviar said, comparing them to singles. "Widowed men and women had 3 percent higher odds, and divorced men and women had 5 percent higher odds of any vascular disease."
Alviar called that degree of risk reduction good, but "not substantial." In younger people, however, the protection for the married men and women was even more pronounced, he said.
Although the researchers found a link between marriage and lower risk for heart disease, they didn't prove a cause-and-effect relationship.
"It's such a large population that you can't cast this study off," said Dr. J. Jeffrey Marshall, past president of the Society for Cardiovascular Angiography and Interventions. Marshall reviewed the findings but wasn't involved in the study.
Although other studies have looked at death rates from heart disease, this study is looking at the odds of getting cardiovascular disease, said Marshall, a cardiologist in Gainesville, Ga.
Neither Marshall nor Alviar could explain the apparent protective factor of marriage, but both have some thoughts about the reasoning behind it. "Maybe married people look out for each other," Marshall said. "They may exercise together. Your spouse may help you watch your diet."
Although the new study did not find gender differences, Marshall said, he finds that many of his male patients with heart problems are "dragged to the emergency room" by their wives.
Alviar agreed that partners might look out for each other. "Those who have a spouse may be more likely to comply with doctors' appointments and medications," he said.
The study findings suggest that doctors might need to be more clued in to the heart risk factors of unmarried patients, Alviar said.
Marshall said he tells patients -- regardless of their marital status -- to follow five simple steps to lower their risk: "Don't smoke; eat a low-fat, low-cholesterol diet; sweat every day; achieve your ideal body weight; and stay on your medicines."
Because this study was presented at a medical meeting, it should be viewed as preliminary until published in a peer-reviewed journal.
To learn more about heart health, see the American Heart Association.