The study specifically focused on chronic stress, which is an ongoing circumstance occurring for more than a year and threatens to overwhelm an individual's resources, such as financial problems, difficulties at work or long-term caregiving.
Participants came from the nationally longitudinal Health and Retirement Study at the U-M Institute for Social Research. The sample included 2,042 married individuals who completed questions about their waist circumference, negative marriage quality, stress levels and other factors in 2006 and 2010. Couples were married for an average of 34 years.
Greater negative quality ties as reported by husbands exacerbated the effects of partner stress on both husbands' and wives' waist circumference.
Interestingly, lower negative quality ties reported by wives exacerbated the effect of wife stress on husbands' waist circumference, said Kira Birditt, a research associate professor at ISR's Survey Research Center.
For the increased risk of obesity, 59 percent of the husbands and 64 percent of the wives were at higher risk of disease in the study's first assessment, whereas 66 percent of husbands and 70 percent of wives were at increased risk at the study's conclusion.
About 9 percent of the participants showed a 10 percent increase in waist circumference, which represented an average increase of four inches of more over four years, the study indicated.
"Marriage has powerful influences on health," said Birditt, the study's lead author. "The stress experienced by partners, and not the individual's stress, was associated with increased waist circumference. This effect of stress was even stronger in particular spousal relationships."
Husbands, she said, usually experience lower negative marital quality and thus greater negative feelings may be less expected and more harmful. Because women tend to report greater negative marital quality, low levels of negative marital quality among wives may be an indicator of a lack of investment in the marriage.
Researchers said the study does not address what to do to lessen stress. However, other findings indicate that it's important for couples to cope with stress together, and that goals created by a couple can be more effective than goals created individually.
Birditt said the findings are applicable to younger couples. Previous research has shown that stress has strong effects on marital quality among this group, too.
"We can only assume that this may translate into health effects, although they are probably not as strong on younger, often healthier, samples," she said.
The study's other authors were Nicky Newton, assistant professor at Wilfrid Laurier University in Canada, and U-M researchers Jim Cranford and Noah Webster.
The findings appear in the Journals of Gerontology: Social Sciences.