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.

Men and women with bad relationships faced equal risks, according to the study. 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.