Researchers examined data from 34 previous studies involving more than two million people. Overall, they found that compared to married people, adults who were divorced, widowed or never married were 42 percent more likely to develop cardiovascular disease and 16 percent more likely to develop coronary artery disease.
Unmarried people were also 43 percent more likely to die from heart disease and 55 percent more likely to die from strokes, researchers report in the journal Heart.
While the study wasn't a controlled experiment designed to prove whether or how marriage might help improve heart health, there are many reasons marriage might have a protective effect including potentially more financial stability and social support, said senior study author Dr. Mamas Mamas of the University of Keele in the U.K.
"For example, it is well known that patients are more likely to take important medications after an event such as a heart attack or a stroke if they are married, perhaps because of spousal pressure," Mamas said by email. "Similarly, they are more likely to take part in rehabilitation which improves outcomes after strokes or heart attacks."
Having a spouse around may also help patients recognize early symptoms from heart disease or the start of a heart attack, Mamas added.
Marriage isn't the biggest predictor of heart disease, however. Well-known risk factors like age, sex, high blood pressure, elevated cholesterol, smoking and diabetes account for about 80 percent of the risk, researchers note.
All of the studies in the current analysis were published between 1963 and 2015 and included people ranging in age from 42 to 77 from Europe, Scandinavia, North America, the Middle East, and Asia.
Divorce was associated with 33 percent higher odds of death from coronary heart disease and a more than doubled risk of death from strokes, the study found. Men and women who divorced were also 35 percent more likely to develop heart disease than married people.
Widows, meanwhile, were 16 percent more likely to have a stroke than married couples, but they didn't appear to have an increased risk of heart attacks.
Even though previous research has linked marriage to better outcomes for patients with heart problems, the current study offers fresh evidence of the risk for people unmarried for different reasons, said Brian Chin, a psychology researcher at Carnegie Mellon University in Pittsburgh, Pennsylvania who wasn't involved in the study.
"Given that previous work has suggested that the health benefits of marriage are significantly stronger for men than women, it was especially surprising that this study found no differences between men and women in how marital status affected cardiovascular disease risk," Chin said by email.
Gender relations may still play a role in the different outcomes for married and unmarried patients, Dr. Stefania Basili of Sapienza University of Rome and colleagues write in an accompanying editorial.
"A wide range of behavioral factors, psychosocial processes, and personal and cultural factors can create, suppress or amplify underlying biological differences in cardiovascular disease," Basili and colleagues write.
Limitations of the study include the lack of data on same-sex couples or the quality of marital relationships, researchers note.
It's possible that single people might not take care of their heart health as much as married individuals, Mamas said.
Regardless of marital status, people can reduce their risk by leading a healthy lifestyle, not smoking, and getting regular physicals, Mamas added. Exercise is important, too.
"I often advise couples to exercise together because they are more likely to stick with it," Mamas said. "Go to the gym together, run together or cycle together - doing activities together strengthens the relationship and improves both partners' cardiovascular health." - Reuters