Researchers at Iowa State University found that divorce was6% likely if the wife fell ill, than if she remained in good health.
In contrast, a husband's health did not change the likelihood of divorce. As part of the study, researchers monitored 2,701 marriages over almost two decades; at the start of the study one of the partners had to be at least 51 years old.
In the end, 32% ended in divorce while 24% led to one of the partners becoming a widow or widower, the research found.
Divorce was more common when couples in the study were younger, whereas death was more likely as got older.
Dr Amelia Karraker, who led the study, explained that illness often can take a serious toll on couples, largely for financial reasons, and can hasten divorce.
For example, the healthy spouse is often the primary caregiver, may have to take sole responsibility of managing the household, and might be the only financial breadwinner.
"There is a difference between feeling too sick to make dinner and needing someone to actually feed you. That's something that can really change the dynamics within a marriage.
"If your spouse is too sick to work, we know that financial strain is a major predictor of divorce in and of itself,' Dr Karraker said.
And the quality of care-giving is also a major factor. Wives are largely less satisfied with the care from their husbands, Dr Karraker said.
She said that men, particularly older ones, often have not been socialised to be caregivers in the same way women often are.
"Life or death experiences may cause people to re-evaluate what's important in their lives. It could be that women are saying, 'You're doing a bad job of caring for me. I'm not happy with this, or I wasn't happy with the relationship to begin with, and I'd rather be alone than be in a bad marriage.'"
Other studies have found married couples have better physical and mental health.
Ironically, Dr Karraker's research shows that illness puts women at risk of losing those health benefits of marriage.
Dr Karraker said: "I think the research shows the potential vulnerabilities for people in society who are sick. There is an elevated risk for depression with illness and now you're also at risk for divorce.
"People in poor health may have less access to beneficial social relationships, which in turn can compromise their health further."