The study, led by Marni Jacobs at the University of California, San Diego involved close to 1,300 women from Rancho Bernardo in Southern California.
The research began in the mid-1980s when the participants were, on average, in their 70s. They were asked how many times they had been pregnant and given birth. They were also asked about lifestyle habits related to heart health, such as smoking and exercise, and their cholesterol, blood pressure, height and weight were measured.
For the next 19 years, the researchers recorded their health, brought the women in for regular clinic visits, sent them annual questionnaires and used death records to track their diagnoses.
The team found that 707 women or 55 percent died of various causes and less than half of these deaths were due to heart diseases. This included cardiovascular failure, heart attacks, and strokes.
Additionally, compared to women who had never been pregnant, those who had at least four pregnancies were 35 percent less likely to die of heart or vascular diseases. They were also half as likely to be killed by a stroke or another condition related to artery build-up and high blood pressure.
“It’s just one more little piece of the puzzle that maybe physicians should be aware of or think about,” said Donna Kritz-Silverstein who was part of the research team.
“Heart disease is one of the biggest problems facing women today. It’s the leading cause of death among women in the United States, but many women don’t perceive themselves to be at risk,” she added.
According to the Centers for Disease Control and Prevention, heart disease kills more than 600,000 Americans a year, about half of them women.
When the researchers only noted the number of times a woman had given birth, then the results also showed that they had lower cardiovascular deaths, but the results were not conclusive as to whether this was by chance or specifically because of childbirth.
The team noted that these findings may simply be due to the smaller sample of women who had four or more kids – 131 of them – compared to the 240 that had been pregnant at least four times in their study.
In the survey, 316 women said they had never been pregnant and 406 had never given birth.
The researchers noted that the survey results may not apply to all postmenopausal women, as the test group had especially long life spans, were relatively well-off financially and had good access to health care.
They said that the results might be due to the protective nature of pregnancy hormones like estrogen as well as the extra social support that comes from having more children that led the women in general to have a healthy heart. They also believe that it might be the reverse case that women who are healthy, get pregnant more easily.
“It’s really hard to tease out” the cause, Kritz-Silverstein said. “We’re just speculating – there’s no real way that we can know that from our data.”
She added that further research in the link between heart health and pregnancy could help establish the relation and find out more about the not-so-obvious factors influencing the heart.
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