In the classic marriage vow, couples promise to stay together in sickness and in health. But a new study finds that the risk of divorce among older married couples rises when the wife -- but not the husband -- becomes seriously ill.

"Married women diagnosed with a serious health condition may find themselves struggling with the impact of their disease while also experiencing the stress of divorce," said Amelia Karraker, a researcher at the University of Michigan Institute for Social Research.

Researchers analyzed 20 years of data on 2,717 marriages from the Health and Retirement Study, conducted by the Institute for Social Research since 1992. At the time of the first interview, at least one of the partners was over the age of 50.

The researchers examined how the onset of four serious physical illnesses -- cancer, heart problems, lung disease and stroke -- affected marriages.

They found that, overall, 31 percent of marriages ended in divorce over the period studied. The incidence of new chronic illness onset increased over time, as well, with more husbands than wives developing serious health problems.

"We found that women are doubly vulnerable to marital dissolution in the face of illness," Karraker said. "They are more likely to be widowed, and if they are the ones who become ill, they are more likely to get divorced."

--EUREKALERT