The benefits of breastfeeding: what does the science say?

Improved cognition

Several studies have highlighted a link between cognition and breastfeeding.

Improvement in eating behaviours

Breastfed babies have more leptin in their bodies than formula-fed babies. Leptin is a key hormone in the regulation of appetite and fat storage. They also regulate their own milk intake and are not passive, unlike bottle-fed babies.
They are better able to regulate their food intake, which helps them develop healthy eating habits [3].

In Kramer's robust study, at eleven and a half years of age, adolescents in the intervention group had lower rates of eating disorders, in both girls and boys. 

Reduced risk of obesity and type 2 diabetes

These data are controversial. Kramer's study indicates that breastfeeding has no effect on the risk of developing overweight/obesity in children.

A review combined various scientific studies to examine the impact of breastfeeding on the risk of developing diabetes and obesity [4].

Potentially lower risk of obesity: among the 11 high-quality studies, the association between breastfeeding and overweight/obesity was weaker, with a 13% reduction in risk.

Potentially lower risk of type 2 diabetes: the risk was lower in subjects who had been breastfed (a 35% reduction in risk).

One explanation for this correlation may be related to the development of different gut bacteria. Breastfed babies have higher levels of beneficial gut bacteria, which may affect fat storage [5].

Please note, however, that these data are observational and simply highlight a correlation between these factors.

Reduction in asthma and eczema

Kramer's study showed no reduction in allergies or asthma in breastfed children. On the contrary, breastfed children tended to have higher rates of allergies and asthma (though this effect was not statistically significant).

These data are at odds with other scientific studies on the subject.

A review of 89 scientific studies examined the link between breastfeeding and the risk of asthma and eczema in children [6].

More or less breastfeeding, in terms of duration, was associated with a reduced risk of asthma in children (aged 5–18 years), and a reduced risk of allergic rhinitis at ≤5 years, although this estimate showed high heterogeneity and low quality. The effect of breastfeeding on this variable is therefore dose-dependent (the longer one breastfeeds, the stronger the effect).

Exclusive breastfeeding for 3–4 months was associated with a reduced risk of eczema under 2 years of age (an estimate based primarily on studies of low methodological quality).

No association was found between breastfeeding and food allergy (an estimate showing high heterogeneity and low quality).

The relationship between breastfeeding and teeth

Malocclusion refers to any deviation or variation from a normal bite (lack of spacing between teeth, overlapping, misalignment, etc.).

A review assessed whether breastfeeding reduces the risk of malocclusions by examining the results of 48 scientific studies [7].

The authors noted that children who had always been breastfed were less likely to develop malocclusions than those who had never been breastfed (66% reduction in risk), those who had been exclusively breastfed had a lower risk of malocclusion than those who had not been exclusively breastfed (46% reduction in risk), and children who had been breastfed for longer were less likely to develop malocclusions than those who had been breastfed for a shorter time (60% reduction in risk). They therefore concluded that breastfeeding reduces the risk of malocclusions.
The biases of this study were controlled; however, no mention is made of dummy/soother use by infants, even though teats can also increase the risk of malocclusions.

This effect may be explained by several hypotheses. The sucking process differs between breastfed and bottle-fed children. Breastfed children display greater facial muscle activity than bottle-fed children, which promotes more appropriate craniofacial growth and jaw bone development. The movement of the lips and tongue during breastfeeding requires the infant to draw out breast milk through a pressure action, whereas for bottle-fed infants the movement to obtain milk is more passive; consequently, there is a greater potential for malocclusion to develop [8].

Furthermore, bottle teats are generally made from a less flexible material, which can exert pressure on the inside of the oral cavity and lead to poor tooth alignment and transverse palatal growth [9].

Breastfeeding and the risk of ear infections

Twenty-four studies, all conducted in the United States or Europe, analysed the effect of breastfeeding on acute otitis media [10]. In pooled analyses, any form of breastfeeding proved protective against ear infections during the first two years of life. Exclusive breastfeeding for the first 6 months was associated with the greatest protection (43% reduction in risk), followed by "more or less" breastfeeding (33% reduction in risk for longer breastfeeding).

These data studied children up to the age of 2 years; beyond this age, there is no evidence that breastfeeding protects against ear infections. However, studies on this topic are limited and the quality of evidence was low, so further studies are needed to determine whether this protective effect persists beyond 2 years of age.

In Kramer's study, no effects of breastfeeding on ear infections were demonstrated in children at 6.5 years of age. This might suggest that such an effect is possible in the short term, but unlikely to persist throughout childhood.

Protects against intestinal diseases

In total, 35 studies involving 7,536 people with Crohn's disease, 7,353 with ulcerative colitis, and 330,222 controls were observed [11]. Ever having been breastfed was associated with a lower risk of Crohn's disease (29% reduction in risk) and ulcerative colitis (22% reduction in risk). Duration of breastfeeding showed a dose-dependent association (the longer the breastfeeding, the greater the reduction in risk), with the greatest reduction in risk when breastfeeding lasted at least 12 months for Crohn's disease (80% reduction in risk) and ulcerative colitis (79% reduction in risk) compared with 3 or 6 months.

This may be due to the fact that breastfeeding influences the infant's microbiome (presence of immunoglobulins in breast milk, prebiotics, etc.).

Similarly, one study showed that formula milk was associated with nearly a fourfold increase in diarrhoeal diseases compared with exclusive breastfeeding in infants both under and over 6 months of age [12].

In a 2014 observational study conducted in premature infants (born before 33 weeks), the effects of breastfeeding versus bovine milk on the risk of necrotising enterocolitis were compared. The authors noted that exclusive breastfeeding in these premature infants reduced the incidence of necrotising enterocolitis (1% for exclusive breastfeeding versus 3.4% for bovine milk) [13].

Reduced risk of mortality

In one article, the authors conducted a review of 13 studies to compare the effect of predominantly, partially, or no breastfeeding versus exclusive breastfeeding on mortality rates during the first six months of life, and the effect of no breastfeeding versus any breastfeeding on mortality rates between 6 and 23 months [14].

RR stands for relative risk; for example, an RR of 3 means that non-breastfed children have a 3 times greater risk of developing the disease being studied than breastfed children.

The risk of all-cause mortality was higher in predominantly breastfed (1.5 times higher risk), partially breastfed (4.8 times higher risk), and non-breastfed (14.4 times higher risk) infants aged 0–5 months compared with exclusively breastfed infants. Children aged 6–11 months and 12–23 months who were not breastfed had a 1.8 times and 2 times higher risk of mortality, respectively, compared with those who were breastfed. The risk of infection-related mortality between 0 and 5 months was higher in predominantly breastfed (1.7 times higher risk), partially breastfed (4.56 times higher risk), and non-breastfed (8.66 times higher risk) infants compared with exclusively breastfed infants. The risk was twice as high in non-breastfed children compared with breastfed children aged 6–23 months.

Breastfeeding could have an impact on the mother's health

A review analysed various scientific studies on the effects of breastfeeding and the associated benefits for the breastfeeding mother [15]. 

The analysis of these studies indicates that breastfeeding for more than 12 months was associated with a 26% and 37% reduction in the risk of breast and ovarian carcinoma, respectively.

The data on cancer risk should be interpreted with caution. These studies show correlations between a reduced risk and breastfeeding, but they do not allow us to conclude that breastfeeding prevents all risk of developing these cancers. Furthermore, there are many types of cancer (hormone-dependent or otherwise, etc.) and they depend on numerous variables, so further in-depth research would be needed to assess the effect of breastfeeding and its precise mechanisms.

To find out more on this subject, visit our article on breastfeeding and breast cancer. 

This review also showed that breastfeeding was associated with a 32% reduction in the risk of type 2 diabetes, and that exclusive and predominant breastfeeding were associated with a longer duration of amenorrhoea [16].

The potential benefit of breastfeeding on mood

A relationship has been observed between breastfeeding and the risk of post-partum depression. An observational study of 137 women indicated that women who breastfeed their children reduce their risk of developing postpartum depression, with effects persisting throughout the first 4 months of the post-partum period. Postpartum depression can also reduce breastfeeding rates, suggesting a reciprocal correlation between these variables [17].

This may be explained by the fact that breastfeeding attenuates neuroendocrine stress responses and may act to improve the mother's mood. More specifically, oxytocin and prolactin, the hormones responsible for lactation, may have beneficial effects on mood. Oxytocin in particular is a hormone that promotes feelings of comfort and relaxation during breastfeeding. Furthermore, it is suggested that lactation attenuates stress responses related to cortisol by reducing levels of stress hormones (particularly cortisol) and by improving sleep [18].

It is one thing to say: "Breastfeeding has benefits for your child, so let me help you discover them, and help you get there if that is your choice" but it is quite another to say: "It is the most important thing you can do for your child, and if it does not work for you, that is very unfortunate and, in the long run, it will have serious consequences." Although no one literally says the latter, that is how many women perceive it.

Some data come from observational studies: outcomes of interest (such as IQ, diabetes, obesity) are examined and correlated with breastfeeding. In most cases, risk estimators can be determined that highlight a correlation without establishing a cause-and-effect relationship.

Observational studies on breastfeeding deserve scepticism, as they all suffer from the same major problem: breastfed infants differ on average from formula-fed infants not only in how they are fed during infancy, but also in virtually every other possible factor — the mother's education, the mother's IQ, poverty, neighbourhood safety, exposure to environmental toxins, ethnicity, and the type and quality of childcare. In scientific terms, breastfeeding is confounded, endlessly.

Human studies, particularly in the field of health, are difficult to conduct. Results must be interpreted with caution, and a single finding does not necessarily demonstrate an absolute truth.

Ideally, several large randomised controlled trials would be conducted, in which mothers would be randomly assigned to breastfeed. Randomised controlled trials are the gold standard in medicine for determining whether a true cause-and-effect relationship exists. In practice, however, such trials are neither feasible nor ethical.

Depending on the stage of lactation, 80 to 50% of breast milk proteins are whey (which contains, among other things, lactalbumin, which enables the production of lactose — a sugar that promotes the absorption of calcium and iron and has a beneficial effect on intestinal bacteria). The whey/casein ratio in human milk fluctuates between 70/30 and 80/20 at the beginning of lactation and decreases to 50/50 at the end of lactation. This proportion is considerably higher than in cow's milk, where whey proteins represent only 18% of milk proteins [19]. 
Furthermore, the caseins in breast milk differ from those in cow's milk; some have bifidogenic effects (protective at intestinal level) and they are also smaller and more digestible for the infant [20].

Moreover, human milk is rich in growth factors and hormones, supporting healthy intestinal growth and reducing gastrointestinal inflammation.

Breast milk is rich in polyunsaturated fatty acids [21]. It contains essential fatty acids such as arachidonic acid and docosahexaenoic acid (DHA), which are the most abundant fatty acids in the human brain, supporting its healthy development. Furthermore, breast milk contains cholesterol, which plays important roles in membrane structure, as a hormonal precursor and in brain development [22].

It contains alpha-lactalbumin, which helps bind minerals (calcium, magnesium) and support the immune system. It also contains antimicrobial and antiviral proteins for the baby's early immune system (lactoferrin, lysozyme and lactoperoxidase).

Breast milk also contains nearly 130 different oligosaccharides, which are beneficial, among other things, for the bacteria in the colon [23].

Finally, breast milk proteins not only provide nutrients and defence molecules, but also directly stimulate the growth of the baby's tissues or organs and support the development of the immune system. [24]

There is still much that researchers do not know about the composition of human milk. For example, breast milk varies from one mother to another, is personalised for the baby, and its nutritional content changes throughout the day and over time to meet the baby's needs. [25] It can also vary according to the mother's dietary choices, environmental factors, or infections. [26]

To find out more, see our article on breast milk composition.

Beyond the potential effects of breastfeeding on the health of the mother and her child, there are many other beneficial effects that cannot be quantified: the pleasure of breastfeeding for both, a sense of wellbeing, bonding, increased sleep time (one study found that parents of breastfed babies slept an average of 40 to 45 minutes more), etc. To find out more, see our article on breastfeeding and sleep.

Of course, not breastfeeding does not mean you will not be close to your child — breastfeeding is one way of creating a bond, but there are others, and it takes nothing away from the love between a mother and her child. 
 

Breastfeeding is a choice — it's your body and your decision!