Clinical Context

Despite World Health Organization (WHO) recommendations to breastfeed children, exclusive breastfeeding prevalence at less than 6 months is only 37% in low‐ and middle‐income countries, and breastfeeding prevalence at 12 months is less than 20% in most high‐income countries. Emerging evidence from multiple individual studies suggests that lactation may lower cardiovascular (CV) risk of breastfeeding mothers in later life.

Study Synopsis and Perspective

In a meta-analysis of more than 1 million mothers, women who breastfed their children had an 11% to 17% lower risk of developing cardiovascular disease (CVD), coronary heart disease (CHD), or stroke, and of dying from CVD in later life than mothers who did not.

On average, the women had 2 children and had breastfed for 15.9 months in total. Longer breastfeeding was associated with greater CV health benefit.

This meta-analysis of 8 studies from different countries was published January 18 in an issue of the Journal of the American Heart Associationdevoted to the impact of pregnancy on CV health in the mother and child.

Breastfeeding is known to be associated with a lower risk for death from infectious disease and with fewer respiratory infections in babies, the researchers wrote, but what is less well known is that it is also associated with a reduced risk for breast and ovarian cancer and type 2 diabetes (T2D) in mothers.

The current study showed a clear association between breastfeeding and reduced risk for CVD in later life, lead author Lena Tschiderer, Dipl.-Ing., PhD, and senior author Peter Willeit, MD, MPhil, PhD, summarized in a joint email to theheart.org | Medscape Cardiology.

Specifically, mothers who had breastfed their children at any time had an 11% lower risk for CVD, a 14% lower risk for CHD, a 12% lower risk for stroke, and a 17% lower risk of dying from CVD in later life compared with other mothers.

On the basis of existing evidence, the researchers wrote, WHO recommends exclusive breastfeeding until a baby is 6 months old, followed by breastfeeding plus complementary feeding until the baby is 2 years or older.

"We believe that [breastfeeding] benefits for the mother are communicated poorly," said Tschiderer and Willeit, from the University of Innsbruck, Austria.

"Positive effects of breastfeeding on mothers need to be communicated effectively, awareness for breastfeeding recommendations needs to be raised, and interventions to promote and facilitate breastfeeding need to be implemented and reinforced," the researchers concluded.

Two cardiologists invited to comment, who were not involved with the research, noted that this study provides insight into an important topic.

"This is yet another body of evidence [and the largest population to date] to show that breastfeeding is protective for women and may show important beneficial effects in terms of CV risk," Roxana Mehran, MD, told theheart.org | Medscape Cardiologyin an email.

"The risk reductions were 11% for CVD events and 14% for CHD events; these are impressive numbers," said Mehran, from Icahn School of Medicine at Mount Sinai, New York, New York.

"The caveat," she said, "is that these are data from several trials, but nonetheless, this is a very important observation that should not be ignored."

The study did not address the definitive amount of time of breastfeeding and its correlation to the improvement of CVD risk, but it did show that for the lifetime duration, the longer the better.

"The beneficial effects," she noted, "can be linked to hormones during breastfeeding, as well as weight loss associated with breastfeeding, and resetting the maternal metabolism, as the authors suggest."

Clinicians and employers "must provide ways to educate women about breastfeeding and make it easy for women who are in the workplace to pump, and to provide them with resources," where possible, Mehran said.

Michelle O'Donoghue, MD, MPH, noted that over the past several years, there has been intense interest in the possible health benefits of breastfeeding for both mother and child.

There is biologic plausibility for some of the possible maternal benefits because the favorable CV effects of both prolactin and oxytocin are only now being better understood, said O'Donoghue, from Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts.

"The current meta-analysis provides a large dataset that helps support the concept that breastfeeding may offer some [CV] benefit for the mother," she agreed.

"However, ultimately more research will be necessary since this method of combining data across trials relies upon the robustness of the statistical method in each study," O'Donoghue added. "I applaud the authors for shining a spotlight on this important topic."

Although the benefits of breastfeeding appear to persist over time, "it is incredibly difficult for women to continue breastfeeding once they return to work," she added. "Women in some countries outside the US have an advantage due to longer durations of maternity leave.

"If we want to encourage breastfeeding," O'Donoghue stressed, "we need to make sure that we put the right supports in place. Women need protected places to breastfeed in the workplace and places to store their milk. Most importantly, women need to be allowed dedicated time to make it happen."

Emerging individual studies suggest that mothers who breastfeed may have a lower risk for CVD in later life, but studies have been inconsistent, and it is not clear if longer breastfeeding would strengthen this benefit, the authors noted.

To examine this, they pooled data from the following 8 studies: 45&Up (Australia, 2006-2009), China Kadoorie Biobank (CKB; China, 2004-2008), European Prospective Investigation into Cancer and Nutrition (EPIC; multinational, 1992-2000), Gallagher et al (China, 1989-1991), Nord-Trøndelag Health Survey 2 (HUNT2; Norway, 1995-1997), Japan Public Health Center-based Prospective Study (JPHC; Japan, 1990-1994), Nurses' Health Study (NHS; United States, 1986), and the Woman's Health Initiative (WHI; United States, 1993-1998).

On average, the women were a mean age of 51.3 ± 2.3 (range, 40-65) years when they enrolled in the study, and they were followed for a median of 10.3 (range, 7.9-20.9) years in the individual studies.

On average, they had their first child at age 24.6 years and had 2 to 3 (mean, 2.3) children; 82% had breastfed at some point (ranging from 59% of women in a US study to 97% in CKB and HUNT2).

The women had breastfed for a mean of 7.4 to 18.9 months during their lifetimes (except women in the CKB study, who had breastfed for a median of 24 months).

Among the 1,192,700 women, there were 54,226 incident CVD events, 26,913 incident CHD events, 30,843 incident strokes, and 10,766 deaths from CVD during follow-up.

The researchers acknowledged that study limitations include potential publication bias, as fewer than 10 studies were available for pooling. There was significant between-study heterogeneity for CVD, CHD, and stroke outcomes.

Participant-level data were also lacking, and breastfeeding was self-reported. There may have been unaccounted residual confounding, and the benefits of lifetime breastfeeding that is longer than 2 years are not clear, because few women in this population breastfed that long.

The research was funded by the Austrian Science Fund. The researchers and Mehran and O'Donoghue have no relevant financial disclosures.

J Am Heart Assoc. 2022;11:e022746.^[1]

Clinical Implications

• Breastfeeding was associated with reduced maternal risk for CVD outcomes.
• Clinicians and policy makers should effectively communicate maternal as well as child benefits of breastfeeding, raise awareness of breastfeeding recommendations, and implement and reinforce interventions to promote and facilitate breastfeeding.
• Implications for the Healthcare Team: WHO recommends exclusive breastfeeding until age 6 months and further breastfeeding until ≥ 2 years, accompanied by complementary feeding.

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