A study from the universities of Cambridge and North Carolina found that women who gave birth to five or more children were 38% more likely to have a heart attack compared with women who carried only one or two pregnancies to term.
The study showed the risks increased with each successive child.
Pregnancy and childbirth each put significant strain on the heart, the researchers suggest, and this is in addition to the stress and demands of raising a larger family which leaves less time for self-care.
Having five or more children was also associated with a 30% increased risk of heart disease – the major cause of heart attacks – as well as a 25% increased risk of stroke and a 17% increase in the risk of heart failure compared with one or two children.
The authors said they hoped the findings would help provide "extra motivation" for parents of large families to take extra steps to protect their heart in other ways, such as diet and exercise.
The report says previous studies have suggested that breastfeeding may help protect the heart, but this research found it did not completely offset the extra risk of having more children.
The study, which is being presented at the British Cardiovascular Society Conference in Manchester, saw the team study data from more than 8,000 white and African-American women from the US who were aged 45 to 64. It also looked at women who had a history of pregnancy loss, through miscarriage or other factors, and found these women had a 60% higher risk of heart disease than women who had one or two children.
They said this is likely to reflect underlying health problems that increase the risk of pregnancy loss as well as heart disease and heart failure.
Dr Clare Oliver-Williams, who led the study at the University of Cambridge, said in the report: “The aim of my research is not to scare women but to bring to their attention as early as possible whether they might be at increased risk of heart attacks. We know that pregnancy and childbirth put a tremendous strain on the heart, and raising children can be very stressful, too.”
She added that the number of children a woman has "is an easy sign" of increased risk, and hopefully this research will provide "extra motivation" to keep healthy.
Professor Jeremy Pearson, associate medical director at the British Heart Foundation, which funded the study, said: “Research like this reminds us that – regardless of the stereotype of the overweight, middle-aged man having a heart attack – heart disease strikes men and women alike.
“As the major cause of heart attacks and strokes, heart disease cruelly tears families apart.
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[link url="https://www.independent.co.uk/news/health/women-more-children-heart-attack-risk-mothers-pregnancy-childbirth-parenting-stress-a8381846.html"]The Independent report[/link]