Postmenopausal women who reached menopause at an earlier age or who never gave birth are at a higher risk for heart failure, according to research published in the Journal of the American College of Cardiology.

Previous research has found that hormones present during a woman's reproductive period may influence her risk for heart disease and women who experience early menopause may be at an elevated risk for heart disease. Hormone levels during the reproductive period may be affected by menstrual cycling and pregnancy.

Researchers examined 28,516 postmenopausal women without cardiovascular disease from the Women's Health Initiative to test associations between total number of live births, age at first pregnancy lasting at least six months, and total reproductive duration with incident heart failure.

During an average follow–up of 13.1 years, 5.2 percent of women were hospitalized for heart failure. Short total reproductive duration was associated with an increased risk of heart failure, which was found to be related to an earlier age at menopause and was more pronounced in women who experienced natural, rather than surgical, menopause.

Women who never gave birth were found to be at an increased risk for diastolic heart failure, a type of heart failure where the left side of the heart does not relax as well as it should. The authors did not find that this relationship was due to infertility. Having more children was not associated with heart failure risk.

"Our finding that a shorter total reproductive duration was associated with a modestly increased risk of heart failure might be due to the increased coronary heart disease risk that accompanies early menopause," said Nisha I. Parikh, MD, MPH, assistant professor at the University of California, San Francisco School of Medicine and senior author of the study. "These findings warrant ongoing evaluation of the potential cardioprotective mechanisms of sex hormone exposure in women."

In an editorial comment published with the study, Nandita S. Scott, MD, co–director of the Corrigan Women's Heart Health Program at Massachusetts General Hospital, said that while the mechanisms of these findings are unclear, their importance and potential impact on women's health is real.

"There also remain many unresolved questions including the mechanisms of estrogen's cardioprotective effect, making this truly a work in progress," she said. "Altogether, these findings raise interesting questions about the cardiometabolic effects of sex hormone exposure over a woman's lifetime and continue to raise important questions for future research."