A lousy marriage might literally make you sick.

Marital strife and other bad personal relationships can raise your risk for heart disease, researchers reported Monday.

What it likely boils down to is stress — a well-known contributor to health problems, as well as a potential byproduct of troubled relationships, the scientists said.

In a study of 9,011 British civil servants, most of them married, those with the worst close relationships were 34 percent more likely to have heart attacks or other heart trouble during 12 years of follow-up than those with good relationships. That included partners, close relatives and friends.

The study, in Monday's Archives of Internal Medicine, follows previous research that has linked health problems with being single and having few close relationships. In the new study, researchers focused more on the quality of marriage and other important relationships.

"What we add here is that, 'OK, being married is in general good, but be careful about the kind of person you have married.' The quality of the relationship matters," said lead author Roberto De Vogli, a researcher with University College in London.

De Vogli said his research team is doing tests to see if study participants with bad relationships have any biological evidence of stress that could contribute to heart disease. That includes inflammation and elevated levels of stress hormones.

Another recent study also looked at quality of relationships but had different results. There was no association between marital woes in general and risks for heart disease or early death. But it did find, over a 10-year follow-up, that women who keep silent during marital arguments had an increased risk of dying compared with wives who expressed their feelings during fights. What appeared to matter more for men was just being married; married men were less likely to die during the follow-up than single men.

That study, of nearly 4,000 men and women, was published online in July in the journal Psychosomatic Medicine.

In De Vogli's study, men and women with bad relationships faced equal risks. Volunteers filled out questionnaires asking them to rate the person to whom they felt closest on several measures. These included questions about to what extent does that person "give you worries, problems and stress?"

They also were asked about whether they felt they could confide in that person, or whether talking with that person made them feel worse.

Over the following 12 years, 589 participants had heart attacks or other heart problems. Those with the highest negative scores on the questionnaire had the highest risks, even taking into account other factors related to heart disease such as obesity, high blood pressure and smoking.

James Coyne, a University of Pennsylvania psychology professor who also has examined the health impact of social relationships, said De Vogli's results "make intuitive sense." But he said the study found only a weak association that doesn't prove bad relationships can cause heart disease.

"It is still not clear what to recommend," Coyne said.

"Do we tell people who have negative relationships to get therapy? They may have other reasons to do so, but I see no basis for them doing so only to avoid a heart attack," Coyne said.

Ending a bad marriage is not necessarily the answer either, he said, given evidence that being unmarried also could be a risk.