Breastfeeding is economical and has been described as "one of the highest impact interventions" in healthcare (Hansen, 2016). It is environmentally safe, mobile, easy to use, does not need to be bought, requires little equipment or preparation time, and affects individuals, health care systems, economies and societies deeply, sometimes with life-long impact for both mother and child. For women, benefits include faster birth recovery, fertility reduction in the lactation period, long-term risk reduction of developing several cancer types related to the endocrine system, hypertension, coronary vascular disease, type 2 diabetes mellitus and thus the metabolic syndrome. Other proposed benefits such as postpartum weight loss, reduced lipidaemia, or osteoporosis prevention are less clear.
Breastfeeding offers several aspects of convenience: Composition of milk is customised to the infant; breastfeeding can take place in any location without having to carry a lot of equipment; it is immediate and does not require time for preparation; it is cheap because it is self-made and needs few tools for preparation. There is no need to worry about hygiene aspects such as water quality or water temperature. It is sustainable, needs no transport to reach the consumer, and leaves an overall favourable CO2 footprint (Hansen, 2016, Rollins et al., 2016)
Breastfeeding improves maternal health by reducing excess bleeding at birth via oxytocin, maternal hypertension, cardiovascular disease risk, and risk for several cancers throughout life. Besides offering health benefits for individuals, the short- and long-term impact on maternal and child health reduce poverty, which improves societies in general. In 2016, authors placed a monetary value on breastfeeding for the first time in The Lancet's series on this topic. The authors considered the impact of cognition, childhood mortality, maternal health, environmental impact and others on societies. They concluded that societies with low breastfeeding numbers lose 302 billion US dollars and 0.49% of world gross national income per year (Rollins et al., 2016). These monetary calculations highlight that governments would be prudent to improve acceptance of breastfeeding in their respective populations and recognise female and child health as contributors to gross national income and thus factors that reduce poverty.
A 20-minute interview with one of the authors of the series can be accessed at the Lancet here.
Breastfeeding supports mother-child bonding. This is mediated via oxytocin, a hormone that regulates the release of milk, and is described in "How lactation works" (→). Oxytocin also induces the postpartum involution of the uterus, which shortens the time in which the uterus contracts to its former size. In turn, this uterus contraction decreases birth related blood losses and thus impacts maternal health directly (Galbally et al., 2011, Uvnäs Moberg et al., 2019, Negishi et al., 1999).
Mothers have little to worry that the child receives the nutrients it needs. When the child is growing according to (inter)national growth charts, it is a good sign that all is well. Breast milk adapts to the child's needs as it matures starting with antibody-rich colostrum followed by transitional and later mature milk (WHO, 2009). The mother will also release more antibodies into the milk when the child is sick for an even better support against infections (Riskin et al., 2012).
During the pandemic with SARS-CoV-2 or COVID-19, the WHO and experts recommend continuing breastfeeding (status 2020-09) based on current insights (WHO, 2020b, WHO, 2020a). Available case studies point towards protective effects of breast milk; to date, the virus has not been detected in milk of suspected/confirmed COVID-19 patients. Mothers with confirmed COVID-19 infections are encouraged to breastfeed while wearing a facial mask and following hygiene measures. These include to wash hands frequently, to wear a medical mask that should be changed when damp, not be re-used, and discarded in the trash after use. The breast should only be washed with soap before feeding if an infected mother just coughed over her exposed skin; washing the breast before every feed is seen as unnecessary (WHO, 2020b). The Centers for disease control and prevention (CDC) of the United States of America and a consensus of European Paediatric Societies each state their active support of the WHO position on continued breastfeeding (CDC, 2020, Williams et al., 2020).
As stated in the Bellagio Consensus, lactational amenorrhoea can be a means of family planning and is a "viable approach to postpartum contraception" (WHO Task Force on Methods for the Natural Regulation of Fertility, 1999). These findings were confirmed in a large study of the WHO with more than 4000 women (WHO Task Force on Methods for the Natural Regulation of Fertility, 1999). The effect is consistent and most effective with exclusive or predominant breastfeeding (Chowdhury et al., 2015). The spacing of pregnancies is supportive of women's' health.
Many studies have investigated aspects of breastfeeding on women's' long-term health. Some aspects have not been in focus, whereas for others, a multitude of data has been generated. For this reason, we consulted (systematic) reviews on the different aspects, which we will share in the following sections. When it comes to the investigation of lactational benefits for the mothers' metabolism, confounding factors compromise some of these outcomes. This is because breastfeeding mothers have different socioeconomic status, higher education, and make different lifestyle choices such as being less likely to smoke compared to mothers that choose to feed formula. These choices affect the insights we can gain about breastfeeding benefits themselves (Stuebe, 2015).
Taken together, science shows that any breastfeeding provides protective effects that can last a lifetime. Efficacy increases from a short-duration (<3 months). The duration associated with significant impact seems the period between 6 ‑ 9 months of breastfeeding and a number of studies indicate the strongest effects for every year of maternal breastfeeding over her lifetime.
Breastfeeding is inversely correlated with a significant reduction for the risk of a number of cancers. These include ovarian (epithelial), breast and endometrial cancers. The reduction of risk for ovarian and epithelial ovarian cancer trough breastfeeding has been suspected early and supported by several meta-analyses since (Li et al., 2014, Whittemore et al., 1992, Luan et al., 2013, Chowdhury et al., 2015). The protective effect is stronger with increased breastfeeding duration and has been mechanistically linked to lactational amenorrhea and anovulation through reduced plasma estradiol concentrations in lactation (Li et al., 2014). Luteinizing hormone and gonadotropins are also involved in ovarian cancers and reduced during breastfeeding (Li et al., 2014). Interestingly, even a short breastfeeding duration of less than 6 months decreased ovarian (epithelial) cancer risk (Modugno et al., 2019, Li et al., 2014); the most efficient protection was observed with a breastfeeding duration of more than one year in some studies (Li et al., 2014) whereas others found significant impact with shorter durations (Sung et al., 2016, Modugno et al., 2019). Over the course of a lifetime, breastfeeding a year or less also provides significant protection that can last at least 30 years (Modugno et al., 2019).
Breastfeeding – in particular for a longer duration – reduces breast cancer risk (Chowdhury et al., 2015). More than 40 studies indicate a 4.3% risk reduction per every year of breastfeeding (Chowdhury et al., 2015).
The mechanism of this protective effect in humans is mostly unknown. Preclinical studies indicate that the underlying mechanism may be linked to several factors increasing the risk of breast cancer. These are the expansion of progenitor cells, increased inflammation, proliferation, and hyperplasia of the ducts as consequence of an abrupt involution of mammary glands and lack of breastfeeding (Basree et al., 2019).
The reduction of endometrial cancers can be added to the multitude of breastfeeding benefits. Two meta-analyses on clinical and case studies, one of which conducted by the epidemiology of endometrial cancer consortium, agree on these findings (Jordan et al., 2017, Ma et al., 2018). As with breast- and ovarian cancer, ever breastfeeding and breastfeeding duration per child reduced the risk of endometrial cancer of up to 11% (Jordan et al., 2017). Ma and colleagues showed a reduction of 7% for every half year of breastfeeding in their analysis (Ma et al., 2018).
It has been suggested that other cancer types are also affected, although the data seems sparse. One example is thyroid cancer (Yi et al., 2016).
Science indicates that breastfeeding affects the metabolic syndrome (MetS) itself and also its contributing factors. The metabolic syndrome is a widespread and complex combination of disorders including abdominal obesity, dyslipidaemia, elevated blood pressure or impaired fasting glucose tolerance (Alberti et al., 2009). These factors alone or together increase the risk for type 2 diabetes mellitus (T2DM), coronary vascular disease (CVD), and non-communicable diseases (Aguilar-Salinas & Viveros-Ruiz, 2019, Saklayen, 2018). Bentley-Lewis and colleagues list female risk factors predisposing for the metabolic syndrome as
Assessment conclusions are mixed and some results lose impact through confounders. Yet, breastfeeding duration seems to affect the metabolic syndrome favourably (Zachou et al., 2019, Nguyen et al., 2017): To put a number on it, one review shares that breastfeeding for one month or longer reduces the odds of developing metabolic syndrome by 22% (95% CI 1-39%) (Bentley-Lewis et al., 2007).
Science is most clear for cardiovascular disease and hypertension: Authors of two independent systematic reviews agreed that breastfeeding and breastfeeding‑duration reduce the risk for cardiovascular disease and that available evidence for reduction of hypertension was most convincing. As opposite the evidence for an effect on plasma lipids was limited (Zachou et al., 2019, Nguyen et al., 2017).
Breastfeeding increases insulin sensitivity and reduces circulating glucose levels, which are both positive signs to counter later development of type 2 diabetes mellitus. Data on type 2 diabetes mellitus itself confirms these findings: Reviews describe observations where diabetes was less likely to occur in breastfeeding women (4.4% vs 9.4% p = 0.01) (Stuebe, 2015). Corrected for confounders, the data from the two Nurses' Health cohort studies in the U.K. showed that cumulative breastfeeding duration for at least a year was associated with a 15% (95% CI 1-27) or 14% (95% CI 7-21%) lifelong risk reduction, respectively (Bentley-Lewis et al., 2007). Similar effects of breastfeeding duration on the reduction of type 2 diabetes mellitus were observed by others as well (Chowdhury et al., 2015).
In contrast to evidence on hypertension, cardiovascular disease or type 2 diabetes mellitus risk, evidence for plasma lipids and obesity remains sparse and contradictory (Lambrinou et al., 2019, Baker et al., 2008, Zachou et al., 2019). Impact of breastfeeding on plasma lipids remains non-conclusive (Zachou et al., 2019, Nguyen et al., 2017, Stuebe, 2015, Bentley-Lewis et al., 2007). This is similar for positive effects on postpartum weight retention, although a cautious trend seems to be emerging that exclusive breastfeeding, breastfeeding intensity and -duration reduce postpartum weight retention(Baker et al., 2008, Lambrinou et al., 2019). The mechanismby which lactation may affect weight loss seems to be hormonally regulated: Lambrinou and colleagues propose that progesterone concentrations decrease postpartum whereas prolactin increases with infant's suckling. This causes oestrogen concentrations to decrease and activates body fat stores to release lipids. A secondary effect of prolactin is the inhibition of lipogenesis supporting the possible decrease of stored body fat (Lambrinou et al., 2019). Energy expenditure does not seem affected (→).
Bone resorption and demineralisation take place during lactation to provide milk minerals. About 5-8% of bone calcium – the equivalent of about 210 mg calcium per day – is used in the first six months in lactating women (Canul-Medina & Fernandez-Mejia, 2019, Ryan & Kovacs, 2019). These losses are restored shortly after cessation of lactation (Ryan & Kovacs, 2019). Although a protective effect on osteoporosis has been proposed, it seems that the evidence to support this hypothesis is insufficient (Victora et al., 2016, Chowdhury et al., 2015). At least it seems that postpartum, women do not experience negative effects from breastfeeding (Yan et al., 2019).
Defining dietary recommendations are challenging: The aim of recommendations is to facilitate a balanced diet by defining an amount of a nutrient which must be consumed daily for health maintenance in a healthy population (EFSA NDA, 2017). Intake recommendations can be seen as guidance, not as rule because in reality, dietary needs differ individually due to age, physical acitivty, metabolicdifferences, ethnicity, health state and other factors. Considering these arguments when guiding a patient, population-targeted dietary reference values may be less accurate than recommendations adjusted for the individual's needs and circumstances (EFSA NDA, 2020).
Thus, it is not surprising that the energy recommendationsfor lactating women by the Institute of medicine (IOM) have been challenged to be inaccurate. The IOM suggested adding 400 kcal/d up to half a year after birth. According to Lambrinou and colleagues, this is either overestimating energy expenditure of ⅓ of women by 450 kcal/d or underestimating by 500 kcal/d in other women (Lambrinou et al., 2019). Instead, some studies indicate that energy expenditure during lactation is unaffected by lactation (Bender et al., 2017). Thus, it seems reasonable to discourage all lactating women from overcompensating energy intake during the breastfeeding period and let the treating health care practitioner suggest this when increased energy requirements are indicated in a particular patient, instead.
Synonyms type 2 diabetes mellitus: diabetes type two, diabetes type II, type-2-diabetes, type-II-diabetes, type II diabetes, diabetes mellitus type 1, diabetes mellitus type I, diabetes mellitus type 2, diabetes mellitus type II
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