Working single mothers may have a higher risk of heart disease and stroke than their married peers, a study suggests.

Researchers examined data on health, work and marital status for almost 11,000 women in Europe and 6,000 women in the U.S. who were born between 1935 and 1956.

The odds of being a single working mother were twice as high in the U.S. as in Europe, with 11 percent of U.S. women in the study and 5 percent of the women in Europe having been in that role at some point in their lives.

Compared with working married mothers, single women with children and jobs were 40 percent more likely to have heart disease, 74 percent more likely to have a stroke and 77 percent more likely to smoke, the study found.

"Work and marriage offer, or at least increase, the possibility of financial and social security," said senior study author Frank van Lenthe of Erasmus University Medical Center in Rotterdam, The Netherlands.

"Losing support from a partner, or the security of a job, may cause stress and result in unhealthy behaviors," van Lenthe said by email.

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In both the U.S. and in Europe, roughly 10 percent of women were single, working and childless, the study found.

More than 31 percent of U.S. women and 25 percent of European women were married mothers who returned to work after a few years out of the labor market.

About 29 percent of European women were married working mothers, compared with 23 percent of American women.

When researchers looked at risk factors for cardiovascular disease, they found working, single and childless women had lower odds of having high blood pressure than working married mothers.

Single women without kids in Europe were less likely to have high blood pressure and more likely to have a history of smoking than their U.S. peers.

Even though single working motherhood was associated with worse cardiovascular health outcomes, researchers didn't find any evidence that this association was stronger for women in the U.S. than in Europe, researchers note in the American Journal of Public Health.

When the study team adjusted the data for U.S. women to make their marital, work and parental status match the distribution for women in Europe, the U.S. women's risk of stroke went down by 1 percentage point and their risk of high blood pressure fell 2 percentage points.

That indicates the differences in "work-life trajectories" between European and U.S. women don't fully explain why American women have much higher rates of heart disease and stroke, researchers say.

One limitation of the study is its reliance on women to accurately report their health and work status at several points in time, the authors note. They also lacked information on the number of children women had, family support, longtime relationships that didn't involve marriage and the hours or type of work done by employed women.

It's possible that financial factors influence the odds of cardiovascular disease, said Margot Witvliet, a researcher at Norwegian University of Science and Technology in Trondheim who wasn't involved in the study.

"Having one child is very different from having two or more, which is often the case for American single mothers," Witvliet said by email. "Perhaps other factors such as economics might be more important. Further research is needed to really understand the situation."