The marital vows to stay true “in sickness and in health” seem to apply more to wives than husbands when one of the spouses becomes seriously ill, according to new research.

Social scientists found that the risk of divorce among older married heterosexual couples rises when the wife, not the husband, experiences a health crisis such as cancer, heart problems, lung disease, or stroke.

“When the wives became ill, about 50 percent of the marriages ended in divorce,” said study author Amelia Karraker, a postdoctoral researcher at the University of Michigan’s Institute for Social Research.

Karraker and her co-author analyzed 20 years of data on more than 2,700 heterosexual marriages. At the time of the first interviews in 1992, at least one of the spouses was over the age of 50.

Only a few prior studies have examined the role of poor health in subsequent divorce, with mixed findings, and most of these investigations examined younger couples, Karraker said.

She noted that the new study, presented recently at the annual meeting of the Population Association of America in Boston, “speaks to a different season of life,” but her data didn’t indicate which spouse initiated divorce.

Prior research suggests that women initiate about two-thirds of divorce proceedings.

If the wife decides to exit the marriage after she becomes ill, it may be because she’s dissatisfied with her husband’s care for her, Karraker said.

If the husband decides to leave, he may do so to pursue a relationship with a healthy partner.

The new study couldn’t explain exactly why the divorce risk is elevated when wives become ill, but Karraker said she hopes to glean insight into these aspects through further research.