Researchers at the University of Utah studied more than 300 middle-aged and older couples who had been married more than 20 years. Each couple answered questionnaires about their relationship and mental state and took lab tests.

They found women in marriages with high levels of strife were more prone to depression and metabolic syndrome, a cluster of symptoms such a thick waist, high blood pressure, high cholesterol and abnormal blood sugar that significantly raise the risk of heart disease.

"What we found is that negative aspects of the marriage – a high level of conflict and discord – were associated with increased levels of metabolic syndrome for women and not for men," said Tim Smith of the University of Utah, who is studying marriage quality and heart disease.

"That seemed to be explained by the fact that women in strained marriages also reported more levels of depression," a known risk factor for heart disease, Smith said in a telephone interview.

The study is being presented at a meeting of the American Psychosomatic Society in Chicago.

Smith, who worked on the study with doctoral student Nancy Henry, said a bad marriage was roughly equivalent to leading a sedentary life in terms of raising the risk of metabolic syndrome.

He said the findings represent one of many factors a woman should address to reduce her risk of heart attack. But he said women should tackle other potentially more serious issues first.