MONDAY, Aug. 22 (HealthDay News) -- New research finds that married people are more than twice as likely as single people to be alive 15 years after coronary bypass surgery, although the findings can't prove that having a spouse has a protective effect.

In fact, the limitations of ethical research may make it impossible to ever prove that marriage is good for your health. Still, the study provides more evidence that having a long-term mate is good for you, said study co-author Harry T. Reis, a professor of psychology at the University of Rochester.

In recent years, a number of studies have hinted at several apparent health benefits of marriage: it may slightly boost the odds of survival from colon cancer, for one thing, and it might help reduce pain in rheumatoid arthritis patients.

The problem is that it's hard to know for sure if marriage directly produces health benefits. It's possible, for example, that people who are naturally healthier are more likely to get married in the first place, maybe because they're happier than sicker folks.

In the new study, researchers tracked what happened to 225 people who underwent coronary bypass surgery from 1987 to 1990. Overall, 124 patients -- 55 percent -- survived for at least the next 15 years: 61 percent of the married patients and 30 percent of the unmarried.

Post-bypass survival odds fell for both unmarried women (only 26 percent of them were still alive at the end of the period) and unmarried men (only 36 percent were still alive). But a whopping 83 percent of happily married women and men were still around, the study found.

However, there was a catch: unhappy marriages -- defined as those in which patients said they weren't very satisfied -- spelled trouble for women. Only about 29 percent of those in unhappy marriages survived, while 60 percent of the men in unhappy marriages did.

There are caveats to the research: the big differences between married women and unmarried women shrunk significantly when the researchers adjusted their statistics so they wouldn't be thrown off by the various ages of the women. And fewer women were in the sample of patients, possibly affecting the results for them.

Why might marriage be good for a patient's recovery? "Marriage gives you purpose in life, and feeling like you have a reason to live is an important part of doing the things you need to do to stay alive," Reis said. "Married people also help each other, remind each other it's time to take their pills. And they probably eat healthier."

On the reverse side of things, he said, "when people are not married and living alone, that's when they really let themselves go, especially when they're in their 60s or 70s and living alone."

However, an actual marriage license isn't absolutely necessary to stay healthy, Reis stressed. There's "every reason to believe" that long-term committed relationships have the same effect, he said.

Why is this study important? "This kind of research may ultimately shed light on some mechanisms behind the association between high-quality marriages and health. This can, in turn, inform health initiatives and policy," said Jennifer Barsky Reese, a researcher into the marriage-health connection and a postdoctoral fellow at Johns Hopkins University School of Medicine's department of psychiatry and behavioral sciences in Baltimore.

The study is published online Aug. 22 in the journal Health Psychology.

More information

There's more on maintaining a healthy marriage at the University of Maryland.