April 24, 2009 — Women who breast-fed for a year or more were less likely to develop hypertension, diabetes, hyperlipidemia, and cardiovascular disease when postmenopausal than women who were pregnant but never breast-fed, a new analysis of the Women's Health Initiative (WHI) has found . Dr Eleanor Bimla Schwarz (University of Pittsburgh Center for Research on Healthcare, PA) and colleagues report their findings in the May 2009 issue of Obstetrics & Gynecology.
"We were able to show that benefits were visible in anyone with six or more months' lifetime duration of breast-feeding," Schwarz told heartwire , with those who reported a lifetime history of more than 12 months' lactation being 10% to 15% less likely to have hypertension, diabetes, hyperlipidemia, and cardiovascular death (CVD) than those who never breast-fed.
She says the findings--from a large data set and one of the first studies to report an effect on vascular events--build on a growing body of literature that demonstrates lactation has beneficial cardiovascular effects, as well as reducing the risk of breast and ovarian cancer. "We've known for years that breast-feeding is important for babies' health; we now know that it is important for mothers' health as well," she notes.
It is imperative that healthcare providers and our society support and educate women concerning the maternal benefits of prolonged breastfeeding.
In an accompanying editorial , ob-gyn Dr Edward R Newton (East Carolina University, Greenville, NC) says: "The findings are dramatic and persuasive." Although he notes some possible limitations of this study, he says, "A strong benefit of prolonged breast-feeding is still observed. It is imperative that healthcare providers and our society support and educate women concerning the maternal benefits of prolonged breast-feeding as well as the well-documented benefits of breast-feeding for the child."
Cardiologist Dr C Noel Bairey Merz (Cedars Sinai Healthcare Center, Los Angeles, CA) told heartwire this is "very nice work, controlled for a number of confounders such as education."
The Risks of Not Breast-Feeding
The study examined 139,681 women enrolled in both observational and clinical-trial cohorts of WHI who had had at least one live birth. The dose-response relationship between the cumulative months women lactated and postmenopausal risk factors for CVD were examined; the average age of the women was 63 years. Lifetime duration of breast-feeding was based on patient recollection, and Schwarz admitted this could have been subject to recall bias, a point that Newton also makes in his editorial.
In fully adjusted models, those who reported a lifetime history of more than 12 months of lactation were less likely to have hypertension (odds ratio 0.88; p<0.001), p="0.008)">
And women who breast-fed for seven to 12 months were also significantly less likely to develop CVD (hazard ratio 0.72) than those who never breast-fed.
Schwarz said: "We saw significant trends; the longer someone had breast-fed, the better." In his editorial, Newton says that prior analyses from the Nurses' Health Study show that women who breast-fed for a lifetime total of two years or more significantly reduced a major predictor for CVD--insulin-resistant diabetes--by 14% to 15% and had a 23% lower risk of incident MI [myocardial infarction].
We can talk about the benefits of breast-feeding but perhaps it is better framed as the risks of not breast-feeding.
Schwarz stressed an important point to heartwire . "It's not that you are better off if you have a baby and breast-feed than someone who's never been pregnant, it's that you are better off than someone who becomes pregnant and does not breast-feed. A woman who becomes pregnant and does not breast-feed is actually putting herself at risk. So we can talk about the benefits of breast-feeding but perhaps it is better framed as the risks of not breast-feeding."
Bairey Merz agrees. "We assume the pathway is that breast-feeding protects, but the association could go in the opposite direction--eg, inability to breast-feed may be a marker of early vascular dysfunction," she suggests.
"Women put themselves at risk by becoming pregnant and not fulfilling the cycle that nature has intended," Schwarz says. "In my mind, the cycle really ends with breast-feeding. During pregnancy, the body stores up a bunch of nutrients with the plan that it's going to release much of this in the form of breast milk, a very calorific food. If this doesn't happen, what we see is that the woman's body pays the price. Breast-feeding really helps bring you back to your baseline, and it helps women recover from the stress test that pregnancy entails."
Study of Physiology During Lactation May Help Tackle CVD in Women
In their discussion, Schwarz et al say their finding that women who breast-fed had lower rates of CVD even after adjustment for body mass index (BMI) "indicates that lactation does more than simply reduce a woman's fat stores. Hormonal effects, such as those of oxytocin, may have significant effects on cardiovascular profiles," they note.
Newton says: "The physiologic reasons for these important observations are largely speculative," but "the antistress, probonding effects of oxytocin and intense skin-to-skin contact found with prolonged breast-feeding certainly contribute to the protective effects," he notes.
Although Bairey Merz acknowledges the findings were adjusted for BMI, she says it is well known from many studies "that women who breast-feed lose the pregnancy weight gain better than those that do not--and this likely contributes to their lower CVD risk. What we do not know is whether breast-feeding preferentially impacts the visceral fat deposits, which would be of specific benefit and should be the focus of research."
"A more intense and focused study of maternal physiology during lactation may give us critical information to limit the scourge of CVD in women," Newton concludes.
- Schwarz EB, Ray RM, Stuebe AM, et al. Duration of lactation and risk factors for maternal cardiovascular disease. Obstet Gynecol 2009; 113: 974-982. Abstract
- Newton ER. Whatsoever a [woman] soweth, that shall [she] also reap. Obstet Gynecol 2009; 113:972-973. Abstract
CVD is the leading cause of death for women in developed counties. Recent studies have suggested that lactation increases a mother's metabolic expenditure and improves glucose tolerance and lipid metabolism and may be of long-term benefit in reducing CVD risk. However, whether these benefits persist beyond menopause is uncertain.
This is a study within the WHI cohort to examine the association between lactation, duration of lactation, and the risk for postmenopausal CVD and its components.
- The WHI involved 161,808 healthy postmenopausal women aged 50 to 79 years and data collection included lactation history, parity, any hospitalizations, and CVD.
- Confirmation of outcomes was by medical records review, death certificates, and description of events.
- Lactation history was assessed at baseline when women with at least 1 live birth were asked about lactation including total months (none, 1 - 6, 7 - 12, 13 - 23, and ≥ 24) and age at last lactation.
- 5 CVD factors were considered at baseline: obesity, hypertension, diabetes, hyperlipidemia, and a history of CVD before enrolment in the WHI.
- Dietary information was assessed with use of a 120-item food frequency questionnaire.
- Excluded were nulliparous women and those with incomplete data.
- This study included 139,681 women with at least 1 live birth.
- 58% reported some history of lactation, and only 6% had a cumulative history of lactation greater than 24 months, with few reporting more than 12 months of lactation per live birth.
- On average, 35 years had passed since last lactation.
- 30% of women were obese, and parous women were more likely than nulliparous women to be obese or hypertensive, but parous women who lactated were less likely than those who had not lactated to be obese or to have hypertension.
- Increasing duration of lactation was associated with lower prevalence of obesity and with a reduced risk for CVD risk factors including hypertension, diabetes, and hyperlipidemia even after adjustment for many variables.
- Women with a lifetime history of more than 12 months of lactation were less likely to have hypertension (OR, 0.88; P < .001), diabetes (OR, 0.80; P < .001), hyperlipidemia (OR, 0.81; P < .001), and CVD (OR, 0.91; P = .008).
- Women with a lifetime cumulative duration of lactation of 13 months or more were less likely to go on to have CVD before enrolling in the WHI (OR, 0.91; P = .008).
- Among parous women who did not breast-feed vs those who breast-fed for more than 12 months, 42.1% vs 38.6% would have hypertension, 5.3% vs 4.3% would have diabetes, 14.8% vs 12.3% would have hyperlipidemia, and 9.9% vs 9.1% would have CVD.
- When incident CVD during 7.9 years of follow-up was examined, the duration of lactation was associated with a decrease in incident CVD in univariable, but not adjusted, models.
- Women with at least 1 live birth who breast-fed for 7 to 12 months were significantly less likely to go on to have CVD (hazard ratio, 0.72) vs women who had never breast-fed.
- The number needed to treat to prevent 1 case of hypertension was 29; for hyperlipidemia, 40; for diabetes, 100; and for CVD, 125.
- In parous women with more than 1 live birth, duration of lactation of 24 months or more was associated with a reduced risk for CVD (hazard ratio, 0.58 for ≥ 24 months for 2 live births and hazard ratio, 0.78 for 3 live births).
- The authors concluded that women who breast-fed their children were less likely to have CVD risk factors when postmenopausal.
- They noted that cumulative lifetime lactation of greater than 12 months was associated with a 10% lower likelihood of CVD vs parous women who had never breast-fed.
- They recommended that breast-feeding in the first year of life be endorsed for both infant and maternal benefits.
- Lactation is associated with a reduced risk for postmenopausal hypertension, diabetes, hyperlipidemia, and CVD.
- Lifetime lactation duration of 13 or more months vs no lactation in parous women is associated with a 10% reduced risk for CVD.