Mothers who breastfeed for the recommended amount of time may have a somewhat lower risk of developing high blood pressure later on, new research suggests.
The findings, from a large study of nurses, do not prove that breastfeeding is the reason for the healthier blood pressure. But they do add to evidence that breastfeeding might have benefits not only for babies, but for moms as well, researchers say.
In general, experts recommend that babies be breastfed exclusively for their first six months, then continue getting breast milk along with solid food until they are a year old.
Breastfeeding is thought to help protect babies against certain common ills, like diarrhea and middle-ear infections. But there's also some evidence that breastfeeding may lower a mother's risk of certain health problems down the road.
Studies have found that women who breastfeed have lower risks of diabetes, high cholesterol and heart disease later in life -- though none of them prove cause-and-effect.
For the new study, researchers looked at the correlation between breastfeeding and later risk of high blood pressure among close to 56,000 US women taking part in the long-running Nurses' Health Study II. All had had at least one baby.
Overall, the study found, women who had breastfed for at least six months were less likely to develop high blood pressure over 14 years than those who had only bottle-fed.
Nearly 8,900 women overall were eventually diagnosed with high blood pressure. But those odds were 22 per cent higher for women who did not breastfeed their first child, versus women who'd exclusively breastfed for six months.
Similarly, women who'd either never breastfed or done so for three months or less were almost one-quarter more likely to develop high blood pressure than women who'd breastfed for at least a year.
That was with factors like diet, exercise and smoking habits taken into account.
None of the findings prove that breastfeeding, itself, gives long-term protection against high blood pressure, according to lead researcher Dr. Alison M. Stuebe, of the University of North Carolina, Chapel Hill.
It's possible that some other factor both hindered women from breastfeeding and contributed to their high blood pressure, Stuebe noted in an interview. A stressful work environment would be one potential example.
On the other hand, it's plausible that breastfeeding has direct benefits, Stuebe said. Animal research has found that the hormone oxytocin, which is involved in breastfeeding, has lasting effects on blood pressure.
It's also known that women tend to have a short-term blood pressure decrease immediately after breastfeeding, Stuebe noted.
If breastfeeding is in fact protective, Stuebe's team estimates that 12 per cent of high blood pressure cases among women with children could be linked to "suboptimal" breastfeeding.
But, Stuebe said, "the point here is not to exhort women to try harder."
"If this is a causal relationship," she said, "then taking away barriers to breastfeeding could make a difference in women's health later on."
One way to help more moms breastfeed successfully would be to get them off to a good start at the hospital, according to Stuebe. The World Health Organization encourages hospitals to take certain "baby-friendly" steps that have been shown to aid breastfeeding -- like not feeding newborns anything other than breast milk, avoiding pacifiers and allowing mom and baby to be together 24 hours a day.
But Stuebe pointed to a 2008 study of 1,900 US mothers that found only eight per cent experienced all six recommended baby-friendly practices at their maternity hospital.
She also suggested some other steps breastfeeding advocates have long called for, including better access to lactation counseling, which is often not covered by insurance; break time at work so women can pump breast milk and paid maternity leave.
Right now, the US requires employers with 50 or more workers to offer 12 weeks of non-paid maternity leave.