Traditional marriage vows often include the promise to remain faithful “in sickness and in health,” but it appears many husbands are not keeping this promise when it comes time to stand by a seriously ill wife.

A new study suggests that married women who are diagnosed with a serious disease are 6 percent more likely to end up divorced than healthy women. As reported by Time, the study examined more than 2,700 marriages with at least one spouse over age 50. While nearly a quarter of the marriages ended with the death of a spouse, nearly one in three ended in divorce.

Researchers do not know for sure why this difference exists, but they have a theory.

Anyone who has ever gone through a major illness, like cancer, or who has supported a spouse or loved one during an illness knows that it can be a highly stressful time. The lead author of the divorce study suggested that this stress can test the marriages of ill women.

In many cases, the author said, the sick wife may object what she feels is inadequate care by her husband. Or the husband may resent having to take on the role of caregiver. In other cases, the situation may simply expose the fact that the marriage is not working, or make an already strained relationship worse.

Interestingly, illness befalling the husband seems to have no impact on the risk of divorce, the study says.

A person dealing with divorce and life-threatening illness at the same time has a lot on their plate. For example, they may be too ill to work, so they may need spousal support, at least temporarily. Special considerations like this should be part of the divorce attorney’s strategy.