Other studies have shown that being single or living alone increases the risk for developing and dying from heart disease. Many of these studies, however, were only among men, the researchers said, while this new study includes both sexes.
"Our study suggests that marriage reduces the risk of acute coronary events and death due to acute coronary events in both men and women and at all ages," said lead researcher Dr. Aino Lammintausta, of Turku University Hospital.
"Furthermore, especially among middle-aged men and women, being married and cohabiting are associated with considerably better prognosis of incident acute coronary events both before hospitalization and after reaching the hospital alive," she said.
The report was published Jan. 31 in the European Journal of Preventive Cardiology.
For the study, Lammintausta's team collected data on more than 15,300 people who suffered heart attacks between 1993 and 2002. Among these people, about 7,700 died within 28 days of their attack.
Looking at the role marriage might play in the likelihood of having a heart attack, the researchers found that unmarried men were 58 percent to 66 percent more likely to have a heart attack, as were 60 percent to 65 percent of single women, compared to members of married couples.
The gap in risk of dying from a heart attack was even greater for single men and women, the researchers said. For single men, the risk of dying within 28 days of a heart attack was 60 percent to 168 percent higher than for married men; for single women, the risk of death due to heart attack was 71 percent to 175 percent higher than for married women.
The odds of dying from a heart attack were increased for unmarried men and women regardless of age, compared with similar-aged married couples, the researchers noted.
Why marriage might have this effect isn't clear. The researchers, however, suggest several possible reasons.
Single people may be more likely to be in poor health, they said. Married people may be better off financially, live healthier lives and have more friends and social support, all of which promotes health. Married people also may be more likely to call an ambulance sooner than single people, the researchers said.
In addition, married couples get better treatment in the hospital and after discharge, the researchers noted.
On the other hand, the researchers suggested, single people may be less likely to follow measures that might help prevent heart attacks -- such as taking daily aspirin, cholesterol-lowering statins and medications to control high blood pressure.
"For better or worse, marriage is associated with better cardiovascular health and a lower risk of death due to an acute coronary event," said Dr. Gregg Fonarow, a professor of cardiology at the University of California, Los Angeles.
The reasons marriage or cohabitation may protect people from heart attacks requires further study, he added. Further research is also needed to establish a cause-and-effect relationship between marital status and heart attack incidence and survival.
To learn more about heart attacks, visit the American Heart Association.