Читать книгу Human Milk: Composition, Clinical Benefits and Future Opportunities - Группа авторов - Страница 15

With 200 million years of mammalian evolution, breast milk has evolved major diversity – for instance a 2% concentration of fat in mare’s milk contrasts with over 40% fat in the milk of the harp seal, where the offspring must survive extreme cold. Nevertheless, the application of evolutionary biology to human breastfeeding requires some special considerations with potential implications for practice [1].

Until relatively recently, humans lived in hunter-gatherer societies, but, in a short period, as intelligent primates, humans changed their environment dramatically, whereas our genes are still ancient. The consequent mismatch between our genes and environment is known as “evolutionary discordance.” As Cordain et al. [2] noted for adult humans, the principal phenotypic manifestation of evolutionary discordance is disease. Thus, it is proposed that the high incidence of obesity and cardiovascular disease (CVD) in modern humans is due to the mismatch between genetic adaptation and our modern diet – an example of evolutionary discordance.

The question of relevance here is whether human breastfed infants are affected by evolutionary discordance and how this should be managed to complement the considerable value of breastfeeding identified later in this article. Thus, modern mothers eat less green leafy plants than our ancestors and presumably have less vitamin K in their breast milk [3]. This may explain the past occurrence of late vitamin K deficiency bleeding in modern breastfed infants – a condition that had a high incidence of intracranial bleeding. Thus, all babies now receive prophylactic vitamin K after birth. A further example is that a consequence of recent migration of human populations into less light-exposed areas of the globe is increased propensity to vitamin D deficiency, which may require vitamin D prophylaxis. An intriguing hypothesis to explain the occurrence of early iron deficiency anemia comes from the observation that piglets put in a concrete pen develop iron deficiency since pig’s milk is relatively low in iron and a concrete pen prevents iron intake from soil [4]. Hallberg [5] speculated that early human infants might have eaten soil to supplement the iron received from human breast milk, but with environmental change and modern public health, modern infants no longer consume iron from soil.

One consequence of the major recent change in the diet of humans is that the n-6/n-3 fatty acid ratio in the diet of hunters-gatherers is believed to be around 1: 1 whereas with a modern Western diet this ratio is around 15: 1, reflecting a relatively low n-3 fatty acid status in modern mothers [6]. The impact of supplementing the diet of a lactating mother with n-3 fatty acids is not established but does at least raise the hypothesis for future testing that nutritional status of the offspring might be further optimized by dietary care of breastfeeding mothers.

In summary, current evidence (see later) shows that breastfeeding is superior to its substitutes on numerous health grounds. Nevertheless, given the evolutionary aspects considered, it is in the interests of population health to identify areas in which nutritional care of breastfeeding mothers or their babies could further improve outcome – a principle already in practice in relation to the use of prophylactic vitamin K and vitamin D in infancy.