Breastfeeding in the Modern World

Author(s):
Andrew M. Prentice et al.

Key insights

There is overwhelming evidence that breastfeeding benefits both infants and mothers, particularly in low-income settings. This certainty has underpinned all efforts to promote breastfeeding, at the global, national, and local levels. Following the precipitate declines in breastfeeding of the 20th century, there are signs of recovery, albeit at a slow rate in many regions. National and international efforts to remove existing barriers to breastfeeding, and the use of proven community-based and family interventions, could result in long-term benefits that not only reduce deaths among children and mothers, but also improve wealth through the enhancement of health and cognitive function.

Current knowledge

There is now a solid body of data which describes the complex mechanisms through which breastfeeding modulates infant development and affects maternal health. In low-income settings, breastfed infants have a 4- to 10-fold reduction in mortality. In high-income populations, this is reflected by a reduction in sudden infant death syndrome, the incidence of necrotizing enterocolitis, and otitis media. There is also strong evidence for reduced infant morbidity such as diarrhea and respiratory infections, with the greatest benefits seen in younger children. Mothers who breastfeed have a lowered risk of breast and ovarian carcinomas as well as cardiovascular events. More subtle observations indicate that breastfeeding creates a period of lactational amenorrhea that aids with birth spacing, such that undernourished mothers are protected from an inappropriately short birth interval.


Practical implications

The latest recommendations by the World Health Organization (WHO) indicate that mothers with suspected or confirmed COVID-19 should still be encouraged to breastfeed, as the benefits substantially outweigh the potential risks of trans-mission. Mothers with HIV are also strongly encouraged to exclusively breastfeed for at least the first 6 months, similar to the general population. However, recommendations may differ according to the country. Other important barriers to breastfeeding include lack of community knowledge, cultural attitudes, and negative experiences of breastfeeding in public. The availability of breastfeeding counselling, adequate maternity leave, and positive workplace interventions are important tools for encouraging breastfeeding.

Recommended reading

Rollins NC, Bhandari N, Hajeebhoy N, Horton S, Lutter CK, Martines JC, et al. Why invest, and what it will take to improve breastfeeding practices?. Lancet. 2016;387:491-504. 

Key Messages

•    There is overwhelming evidence that breastfeeding benefits both babies and mothers especially in low-income settings.
•    National and international efforts to remove existing barriers to breastfeeding, and proven community-based and family interventions, could substantially reduce deaths among children and mothers and improve wealth by enhancing IQ and school attainment.

Keywords

Breastfeeding • Exclusive breastfeeding • Initiation of breastfeeding • Barriers to breastfeeding • Benefits of breastfeeding

Abstract

Background: Social changes in the 20th century resulted in substantial reductions in the prevalence of breastfeeding in many countries but especially in those with high and increasing wealth. Concerns about this decline prompted widespread research to quantify the benefits of breastfeeding and the mechanisms by which it exerts protective effects for mothers and children. Pro-breastfeeding advocacy resulted in the WHO International Code of Marketing of Breastmilk Substitutes in 1981 and the Innocenti Declaration on Breastfeeding in 1990, which, together with numerous other initiatives, have helped to turn the tide. Summary: A tranche of recent meta-analyses of dozens of individual studies provide

very strong evidence that breastfeeding has substantial benefits to babies, infants, and young children. The benefits and strengths of association vary according to the background environmental and hygiene conditions in different settings. In low-income settings, the chief measurable benefits for the child are in respect of reductions in diarrhea and respiratory infections, and in mortality. In high-income settings, breastfeeding protects against otitis media, likely protects against type 2 diabetes and overweight and obesity, and possibly protects against type 1 diabetes. It likely improves IQ by 2-3 percentage points. In mothers, breastfeeding reduces a mother's likelihood of breast and ovarian cancers. Feeding these data into the Lives Saved Tool suggests that these benefits could prevent 823,000 deaths in children and 22,000 among women.    

Introduction

Breastfeeding - aptly termed “an ancient art and a modern miracle” - has multiple proven benefits for babies, their mothers, and their societies and should thus be cherished, promoted, and protected. The rapid social and economic changes affecting our world can have diverse effects on breastfeeding practices. As low-income countries advance, traditional values, including breastfeeding, are under pressure. On the other hand, in many high-income countries, an appreciation of the enormous benefits of breastfeeding has driven a more  
enlightened approach to issues such as maternity leave and regulation of the inappropriate promotion of milk formulas, which are gradually helping to increase the prevalence of breastfeeding, albeit from a low base.
In 2016, The Lancet published two coordinated papers drawing together the latest evidence based upon a series of newly commissioned meta-analyses and market research [1, 2]. The current review is based heavily upon these excellent papers augmented by additional more recent analyses.

The Latest Evidence on the Benefits of Breastfeeding

There are numerous comprehensive reviews available, which summarize the benefits of breastfeeding and the mechanisms by which these are achieved (e.g., [3]). They describe an array of increasingly understood complex pathways by which breastmilk has evolved to optimize child survival in eons past. These remarkable mechanisms are worthy of study, but the keenest observer may also question whether breastmilk is still optimized for child development now that babies are so much less vulnerable to early infections. A key example of how breastmilk might not now be optimal is in respect of its iron content [4, 5], a matter of active research by our research group. Over evolutionary time, it appears that iron levels in milk were maintained very low in order to avoid promoting pathogen growth. Modern medicine now considers these levels to be potentially constraining brain and cognitive development, and many countries recommend early iron supplementation in breastfed babies, especially those born prematurely or at low birthweight. Notwithstanding these nuances, breastfeeding remains a powerful force for good health across that world.

Breastfeeding Reduces Morbidity and Mortality Rates in Young Children

There is overwhelming evidence that breastfeeding protects against death in low-income settings. Twenty-eight meta-analyses have addressed this issue. Methodologies vary according to the available definitions of breastfeeding in the source papers (e.g., ever vs. never breastfed, short vs. long breastfeeding), but despite these limitations, there is a very strong consensus that breastfeeding reduces mortality by between 4- and 10-fold in low-income settings [1, 6, 7].

Separate meta-analyses suggest that breastfeeding can additionally reduce child deaths in the low mortality settings of high-income countries. For instance, meta-analysis of 6 studies suggests a 36% reduction in sudden infant death syndrome among ever breastfed babies and meta-analysis of 4 studies shows a reduction of 58% in necrotizing enterocolitis [8].

The evidence for morbidity is even stronger. Meta-analysis of 66 studies, most of which were in low-income settings, shows a very clear protection against diarrhea and respiratory infections, with estimated reductions of about a half for diarrhea and a third for respiratory infections [9]. Protection by breastfeeding against more severe forms of each of these (judged by the need for hospitalizations) is estimated to be even stronger: 75% for diarrhea and 57% for respiratory infections [9]. All of these effects are strongest in younger children.

In high-income settings, there is evidence of protection against otitis media in children younger than 2 years, but not in older children [10]. Evidence for protection against food allergies, eczema, and allergic rhinitis is unconvincing, and a marginal protection against asthma (9%) disappears when the analysis is constrained to studies with more rigorous control of confounding [11].

In young children, breastfeeding is found to protect against dental caries in an analysis of 49 studies [12]. However, longer breastfeeding (for over 12 months) and nocturnal breastfeeding are associated with a 2- to 3-fold increase in dental caries in older children (>12 months).

Growth Outcomes

A meta-analysis of 17 studies (which includes 15 randomized trials of breastfeeding promotion, most conducted in middle-income countries) shows no difference in growth outcomes except for a very marginal possible reduction in BMI [13].

Later Obesity

Evidence of the effects of breastfeeding on the risk of overweight and obesity is equivocal, though the latest meta-anal- ysis of observational studies suggests a 13% reduction [13].

Later Noncommunicable Disease Risks

Meta-analysis of 11 available studies suggests that breastfeeding could provide a 32% reduction in type 2 diabetes, but when re-stricted to the only 3 studies deemed to be of high quality, this drops to 24% and is nonsignificant with high heterogeneity [14]. There is a possible protection against type 1 diabetes when 6 studies were combined [14] but no apparent impact on blood pressure or cholesterol levels (analysis ranged from 38 to 46 studies). Breastfeeding shows an aggregate protection of 19% against childhood leukemia in an analysis of 18 studies [15].

Intelligence

It is notoriously difficult to adjust for confounding in studies of breastfeeding and intelligence (brighter mothers are more likely to breastfeed their children) and to eliminate possible residual confounding. Nonetheless, most analyses suggest a 2-3% point improvement in a range of measures of IQ after best efforts to adjust for home environment and parental IQ [1, 16-18], and numerous studies suggest improvements in attained years of schooling [1].

Breastfeeding Has Health Advantages for the Mother

Birthspacing


Numerous studies over many decades show that breastfeeding creates a period of lactational amenorrhea that aids with birthspacing [1, 15, 19, 20], an effect that is mediated by pro-lactin and is regulated by a mother's energy balance [21] in a manner such that undernourished mothers are best protected from an inappropriately short birth interval that would harm the mother herself and her children.

Breast and Ovarian Cancers

Extensive and well-powered meta-analyses show that ever versus never breastfeeding and longer versus shorter breastfeeding have a measurable protective effect against breast [19, 22] and ovarian [19] cancers. When restricted to the best controlled studies, longer versus shorter breastfeeding is associated with a 7% reduction in breast cancer and an 18% reduction in risk of ovarian cancer [19].

Cardiovascular Disease

A very recent meta-analysis of 8 studies involving almost 1.2 m parous women reveals the following reductions in cardiovascular outcomes among women who had ever breastfed compared to those who had never breastfed: 11% for cardiovascular disease (CVD), 14% for coronary heart disease, 12% for stroke, and 17% for fatal CVD [23]. However, in individual studies adjusted for socioeconomic status and, in some studies, additional variables, there remains the possibility that these associations arise from residual confounding whereby certain behavioral traits may have parallel effects on likelihood of breastfeeding and later likelihood of CVD.

Osteoporosis

Bone is used as a reserve to help supply calcium in breastmilk and breastfeeding is thus associated with some dynamic changes in bone mineral density [24, 25], but meta-analysis of the 4 available studies found no association between breastfeeding and subsequent osteoporosis [19].

Type 2 Diabetes

Meta-analysis of 6 cohort studies indicates a 32% reduction in the likelihood of developing type 2 diabetes [26].

Postpartum Weight Change

Although fat tends to be accrued in pregnancy especially in gynoid regions and there is solid biochemical evidence that this is an evolved mechanism to subsidize the energy needs of subsequent lactation [27], patterns of weight change postpartum are very variable and weight loss is by no means inevitable. Overall, the evidence that breastfeeding influences postpartum weight change in any consistent direction is inconclusive [28]. However, an analysis of data from 740,000 British women showed that each additional 6 months of lifetime breastfeeding was associated with a 1% lower BMI [29].

Maternal Depression

There is an inverse association between breastfeeding and maternal depression, but the direction of causality is uncertain and it seems most likely that the least depressed women would be more likely to successfully breastfeed [30].

Latest Recommendations on Breastfeeding by Mothers with HIV or COVID-19

HIV

Provision of lifelong antiretroviral therapy and/or prophylaxis should be the mainstay of the care of mothers living with HIV. Whether or not this is provided, the latest WHO advice (updated in February 2019) is as follows: “Mothers known to be HIV-infected (and whose infants are HIV uninfected or of unknown HIV status) should exclusively breastfeed their infants for the first 6 months of life, introducing appropriate complementary foods thereafter, and continue breast feeding. Mothers living with HIV should breastfeed for at least 12 months and may continue breastfeeding for up to 24 months or longer (similar to the general population)” [31].

Recommendations differ in many countries. For instance, the US CDC and the American Academy of Pediatrics recommend against breastfeeding by HIV-infected mothers [32].

COVID-19

WHO recommends that “mothers with suspected or confirmed COVID-19 should be encouraged to initiate or continue to breastfeed. Mothers should be counselled that the benefits of breastfeeding substantially outweigh the potential risks for transmission” [33]. In contrast to their position on HIV, the US CDC provide advice on precautions for breastfeeding with COVID rather than making an explicit recommendation and currently do not advise against breastfeeding with COVID [34]. The US Centers for Disease Control's latest advice is that breastfeeding mothers can safely receive the Pfizer or Mod- erna vaccines, though whether this provides any protection to their baby is still unknown.

Estimates of Lives Saved and Saveable by Breastfeeding Using the Lives Saved Tool [35], Victora et al. [1] estimated that if breastfeeding was scaled up to be almost universal in 2015, it would have saved 823,000 lives in 75 high mortality LMICs. They estimated a reduction in deaths from breast cancer of 20,000 per year if current breastfeeding rates in high-income countries were raised toward the global average compared to a modeled scenario with no breastfeeding. They estimated that increasing breastfeeding rates at 1 year in high-income settings and at 2 years in LMICs could potentially save a further 22,000 lives.

Recent Trends in Breastfeeding Worldwide

Indicators Used to Assess Breastfeeding Prevalence and Trends

Meaningful comparisons of breastfeeding rates across nations and across time would ideally be based on standardized definitions (see Box 1) and standardized protocols for assessing prevalence against such measures.


Unfortunately, surveys often use alternative definitions, and few surveys from high-income countries report on these standardized indicators; hence, proxy estimates often have to be constructed to permit comparisons [1]. Notwithstanding these limitations, Victora et al. [1] estimated global trends in breastfeeding and their results are cited here.

Breastfeeding Rates across the World

Figure 1 shows the global prevalence of breastfeeding at 1 year and demonstrates encouragingly high rates in most of Africa and south Asia. Figure 2 consolidates the data by national wealth categories and presents additional indicators. In low- and lower-middle income countries, the proportions of babies ever breastfed and still breastfeeding at 6 months are very impressive, exceeding 90% on average. Levels of exclusive breastfeeding 0-5 months are about 50% in the lowest-income countries, decline with increasing wealth, and are unavailable for the high- est-income countries. Thus, breastfeeding is one of the few health indicators that show better statistics for low-income countries. Figure 3, also reproduced from Victora et al. [1], shows the association between the proportions of babies exclusively breastfed at 0-5 months and the proportion still breastfeeding at 1 year. In most regions, there is an unsurprising correlation between the two indicators, but in West Africa, there are countries with very low exclusive breastfeeding rates yet very high levels of babies still breastfed at 12 months.