In the past decade, breastfeeding rates have increased substantially. Between 2000 and 2015, the proportion of infants who continued to breastfeed at 12 months increased from 16% to 36%. The proportion of infants who had any breastfeeding increased from 71% to 83%.1 While the infant health benefits of breastfeeding are widely recognized, the maternal health benefits of breastfeeding are many and likely underappreciated.
Infant health benefits of breastfeeding
There are no large-scale, randomized studies of the long-term health benefits of breastfeeding versus formula feeding. The evidence supporting the health benefits of breastfeeding is derived from case-control and cohort studies. Breastfeeding directly benefits newborn and infant nutrition, gastrointestinal function, host defense, and psychological well-being. Compared with formula-fed newborns, breastfed infants have a reduced risk of infectious diseases including otitis media, gastroenteritis, respiratory infections, sudden infant death syndrome, and metabolic disease. These benefits alone strongly support the public health benefit of breastfeeding.2 In addition, breastfeeding greatly benefits maternal health.
Maternal health benefits of breastfeeding
Breastfeeding reduces a woman’s risk for type 2 diabetes, hypertension, and coronary artery disease, myocardial infarction, as well as breast, ovarian, and endometrial cancer. There are few exposures that have such a multitude of positive health benefits.
Type 2 diabetes
In a prospective cohort study of 1,238 women without diabetes in 1985–1986, 182 women developed type 2 diabetes after 30 years of follow-up. Compared with never breastfeeding, breastfeeding for 0 to 6 months, >6 months to <12 months, or ≥12 months reduced the risk of type 2 diabetes by 25%, 48%, and 69% respectively.3 In the prospective Nurses’ Health Study, among parous women, each additional year of breastfeeding decreased the risk of type 2 diabetes by 15% compared with women who did not breastfeed.4
In the Women’s Health Initiative (WHI) study of postmenopausal women, a lifetime history of breastfeeding for 12 months or more was associated with a 12% decrease in the risk of hypertension.5 For parous women, the prevalence of hypertension among breastfeeding (≥12 months) and never breastfeeding women was estimated to be 38.6% versus 42.1%.5 Similar results were observed in the Nurses’ Health Study II.6
Myocardial infarction and coronary heart disease
In the prospective Nurses’ Health Study, during 1,350,965 person-years of follow-up, 2,540 women had a myocardial infarction (MI). Women who had breastfed for ≥ 2 years had a 37% decreased risk of MI compared with women who never breastfed. After adjustment for family history, lifestyle factors, and adiposity, the observed reduction in risk was 23%.7 In the WHI (observational study plus controlled trial), women with a single live birth who breastfed for 7 to 12 months had a lower risk of cardiovascular disease than women with a single live birth who did not breastfeed (hazard ratio, 0.72; 95% confidence interval, 0.53–97).5
In a systematic review and meta-analysis of 100 publications, breastfeeding >12 months reduced the risk of breast cancer by 26%.8 In a systematic review of 47 studies, the relative risk of breast cancer decreased by 4.7% for every 12 months of breastfeeding.9 In a systematic review and meta-analysis of 3 studies, ever breastfeeding was associated with a 28% reduced risk for triple-negative (ER-, PR-, HER2-) breast cancer among parous women.10 Triple-negative breast cancer generally has a poorer prognosis than receptor-positive breast cancers.
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