Breast Milk
By: Anna Sarreither
Tags: Baby, Motherhood, Pregnancy, Breastfeeding, Parenting

Breast Milk

Photo by Fanny Renaud on Unsplash

written by Anna Sarreither - Pediatric Nurse

Introduction

It is widely known that breast milk offers the best nutrition for your baby. However, did you know that it is able to change during the lactation period, that it can change its composition during the day, between mothers and within the population? Generally, human breast milk consists of 87 % water, 3,8 % fat, 1,0 % protein and 7 % lactose. It is a dynamic substance, which changes with time, adapting to the growing baby’s needs. (1) To fully understand how lactation works, I will begin by explaining what is meant by lactation.

Lactation is defined by the medical dictionary, Pschyrembel, as a summarizing term for milk production (synthesis) and milk secretion by the female breast during the breast-feeding period. (2)

Stages

The first stage of milk production is called mammogenesis. At this stage, the colostrum is produced and this production is regulated by hormones. Due to rinsing hormones in the mother’s blood, which are additionally produced by the placenta, the alveoli in the pregnant woman’s breasts convert their cells from epithelial cells to secretory cells. These hormones are called prolactin, relaxin and HPL (Human Placental Lactogen). The mammogenesis starts from approximately week 12–16 of pregnancy and ends most likely on the second day after the newborn’s birth. Due to oestrogen and progesterone, which are the hormones that keep the pregnancy going, lactogenesis is inhibited, which means only a small amount of colostrum can be produced during pregnancy. (3) (4)

The second stage is called lactogenesis, which produces the transitory breast milk and this stage is also regulated by hormones. Since the placenta hormones decrease, due to the placenta missing after birth, they do not inhibit the lactogenesis any longer and the breasts can now produce milk to their full potential. This normally starts on day 3–4 after birth. Since all of this is a process and does not work just by flipping a switch, this phase can last up to day 8 after birth. (3) (4)

The third stage is called or galactopoesis. This process maintains lactation once it has been established. It is stimulated by the newborn sucking on the mammilla (nipples), which releases the hormones prolactin and oxytocin. Prolactin stimulates the new production of milk for the next feed, also called lactation reflex. (3) (4)

The fourth step is called galaktokinesis or also known as the let-down-reflex. This process maintains the milk flow during a feed. This is induced by the baby sucking on the mother’s mamilla, which is stimulated, as already mentioned above, by oxytocin. Oxytocin then stimulates the myoepithelium (muscle cells in the milk ducts) to contract and thereby releases the breast milk through the mamilla. Without this process, a baby would not be able to feed from the breast since its suction would not be strong enough. (3) (4)

The last step is called involution. This process begins, when the baby is no longer breastfed. This happens approximately 1–2 months after the last feed, since the breast is no longer empties. This signals that milk is no longer needed and induces the regression of milk production tissue in the breast. (3)(4)

Good to know

A common mistake made when thinking the amount of milk produced is that one presumes that the amount of milk produced depends on the size of the mother’s breast. One of the two key factors in the amount of milk produced, is how much milk secretory tissue one possesses. Woman with smaller breast can have a lot of secretory tissue and therefore produce a lot of milk, while woman with bigger breast may have a smaller amount of tissue and produce a smaller amount of milk. The other point that milk production depends on is the amount of milk removed from the breast either through the baby suckling or via breast pump. Additionally, to all the other components in the milk, there is a protein factor called ‚feedback inhibitor of lactation‘ secreted into the alveoli of the breasts. If there is no milk removed, the protein interacts with the cells and inhibits further milk secretion. One does not fully understand which substance in the protein it is or how it actually works, one just knows that it interacts with the secretory tissue. (5) In addition, the composition of the milk changes during one feed. The milk, which the infant receives first, also called foremilk is thinner, with a higher content of lactose. This satisfies the baby thirst. After that the ‘hind milk’ follows, which has a creamier consistency, due to a higher amount of fat. (5)

Colostrum

Colostrum, also called drinkable gold, has a thick consistency, due to it high cell count and a yellowy colour due to its high consistency of ß — Carotin. It contains a large amount of protein, for example immunoglobulins and stem cells, which are very important for the newborn’s immature immune system. There are also higher counts of Vitamin. A, Vitamin. E, lactose and minerals in the colostrum, than in mature breast milk. Other positive effects are, that is stimulates the newborn’s bowl system to pass the first stool, called meconium. With the meconium, the newborn also passes a substance called bilirubin. Through that, the chance for the newborn developing a newborn icterus is reduced. It also promotes the growth of Lactobacillus bifidus, which is important for the development of a healthy gut flora (6). Additionally, it has shown to have a stabilizing effect on the newborn’s blood glucose level. During the first 24h after birth, the newborn drinks approximately 7–10 ml of colostrum per feed. This may seem a small amount, but since the stomach of a newborn is still very small for the first days and its drinking feeding routine is every 1–3 hours, this assures that this is enough fluid and calorie intake. One should also keep in mind, that the baby still has amniotic fluid in it stomach and bowl system, which has to be digested and provides some fluid and nutrition at first. Studies are still searching how big the stomach of a newborn actually is after birth. Nils Bergmann suggests it has the volume of approximately 20 ml (7), others say it is the size of a cherry or marble. (8) However, the small amount of colostrum does have a function. It aims to provide a low volume, to help the newborn establish a suck, swallow and breathing cycle during a feed. (9)

Transitory Milk

The transitory milk is the product of colostrum and mature milk. When the change of colostrum to mature milk starts at approximately day 3–4, one can see a difference in the milk composition on day 5. This transition stage can last up today 15 days after birth, resulting in mature milk thereafter. (10)

Mature milk and its composition

On approximately day 15 after birth, the breast milk has reached its ‘mature state’. Breast milk now contains lower amounts of protein than animal milk, which is good since protein can put strain on the kidney function and the delicate body circulation of the newborn. The whey amount of protein is higher in breast milk than in formula, making it easier for the newborn to digest. (11) The protein, which is contained in the milk, has immune specific substances, which are anti-infective and anti-inflammatory. Lactose, fat and the calorie amount is specifically adjusted to help the newborn gain weight and grow. These are only a few common composition groups of breast milk. Breast milk also contains various other nutrients which are very important for: the immune system, bowl development, nervous system development, growth factors, hormones which regulate feeding patterns, enzymes which help chemical reactions in the body, vitamins, protein for muscle and bone development, proteins for antibacterial defence, as mentioned carbohydrates as an energy source, non-protein nitrogen which build a sources for the actual proteins or make it possible to actually use fatty acids as energy source, nucleotides which are the building source for DNA and RNA, Erythropoietin which is responsible for the development of red blood cells and a lot more. (12) As already mentioned above, breast milk adjusts to the infant’s needs. Studies have shown that breast milk has a positive effect during an infection and even decreases the duration of some infections, for example diarrhoea (14). One is still researching how the mechanism works. One hypothesis is that the woman’s breast can detect the infection through the salvia, which the infants transfers via latching onto the breast. One certainly knows that the white blood cells increase in the breast milk if the child has an ongoing infection. For further information about the mechanism further studies are needed. (15) Many studies over the years have indicated that breast milk composition depends on the mother’s diet. A study by Ballard et al, published in February 2014 suggest that micronutrients, as well as Vitamins A, B1, B2, B6, B12, D, iodine, vary in their amount depending on the maternal diet and body stores. (16.1) Another study published in May 2020 by Zavadska et al, showed that macronutrients like fat, protein and lactose is not effected by maternal diet, but the fatty acid composition is immediately effected. (16.2) Interestingly, breast milk also works as a clock for the newborn, via the sleeping hormone melatonin and the stress hormone cortisol. Since a baby does not produce melatonin itself until the age of 3 months (17), it is transferred from the mother’s blood circulation through the breast milk to the newborn. Melatonin is released in one’s body when being surrounded by darkness. On the other hand, cortisol is highest around 7–9 am. Cortisol awakes us due to its function of rising the blood glucose level. The lowest cortisol level can be detected at around 10 pm. Furthermore, studies have researched if melatonin, which has a relaxing effect on smooth muscles, which are also presented in the gastrointestinal tract, may also sooth infantile colic. (18) A study, published in 2019, by Alhadi Alhindi et al, examined if breast milk changes its composition when one gives birth to female or male baby. The study group did see changes in ‘Higher value of viscosity and higher percentages of protein and acidity’ in breastmilk of boys than in girls. This could indicate that there is a difference between the milk provided for either a boy or a girl. (19) Moreover, one knows that breast milk possesses a large amount of the protein called HAMLET, which potentially can be used in cancer therapy — studies have only just started researching this. (20) A small study has shown that HAMLET is able to detect tumour cells and destroy them. Whether or not it can be used in cancer therapy is still not completely certain. To gain further knowledge scientists will have to run more studies. (21) (22).

Positive short and long-term outcomes of breastfeeding for the mother

In the short term, breastfeeding stimulates uterus contraction, due to the release of oxytocin, while the baby feeds. This quickens the uterus involution, which also decreases the risk of endometritis puerperalis (infection of the endometrium after birth). It reduces stress, since this is a feature of prolactin, lowers postpartum depression if one already had prenatal depression (23), may be a contribution to more rapid weight loss and mostly likely prolonged anovulation, which then mostly likely prevents the mother from conceiving whilst breastfeeding.

In the long term, breastfeeding can decreases the risk of getting breast cancer by every year one breastfeeds up to 4,3 %. (24) In addition, Danforth and colleagues found, that if one breastfeeds for over 18 months in comparison to a woman who has never breast fed, the risk of getting ovarian cancers decreases by 50 %. They have also shown that the relative risk decreases by 2 % every month of breast-feeding (25) It is still being discussed why this is the case. Schwarz et al, ‘found a 10–20 % higher risk of diabetes, hyperlipidemia, and cardiovascular disease among parous women who had never breastfed compared with those who had breastfed for 13 to 23 months‘ (26) Jonas et al, who published a paper in 2008, regarding the positive effect of breast-feeding on the mother’s blood pressure, showed that, blood pressure falls during a feed and decreases during the first 6 months of breast feeding in relation to blood pressure before breast feeding. (27) This is mostly likely due to the release of oxytocin. (28) Breastmilk is also known to sooth irritation and work as a natural balm on the mother mamilla.

Positive long — term outcomes of breastfeeding for the infant

SIDS Prevention

It is well known nowadays that breastfeeding is one of the key indicators in preventing Sudden Infant Death Syndrome. (29)

Cognitive Function

In the three months after birth, the brain mass nearly doubles. By the age of two, the brain has approximately reached 80% of the fully-grown brain of adults. The different areas of the brain are connected by the white matter, which allows certain areas to communicate. Studies have shown that breast fed babies have an improved development in late maturing white matter compared to formula fed babies. Likewise, an extended duration of breast-feeding was associated with improved white matter structure and cognitive performance. (30). Additionally, another study by Horta et al, published July 2015, presents that breast fed children showed improved performance in intelligence tests. (31)

Weight

Horta also published a paper, showing that breast fed children have a 13 % lower chance of becoming overweight, or being obese as well as reducing the odds of type 2 diabetes. (32) Stopping breastfeeding before 6 months also showed a three times bigger chance of obesity in the first year of life. (33)

Eyes

A study by Birch et al, published 1993, presented, that children, who have been breast fed have a better visual evoked potential, forced-choice preferential-looking, random dot stereo acuity and letter matching ability. This is due to DHA (unsaturated fatty acid, which is presented in the retina) and arachidonic acid (unsaturated fatty acid) which is important for the visual development in the first year of life. (34)

Jaw

Also in 2015, Glazer Peres et al, published that breastfeeding decrease the risk of malocclusions. (35) Tham et al, also connects breastfeeding with the protecting of dental decay in infants under the age of 12 months. (36) Additionally, D C Page, published a paper 2001 saying: ‘Breast suckling aids proper development of the jaw which form the gateway to the human airway.’ (37)

Ears

A study by Bowatte et al, presented that exclusive breast-feeding for the first 6 month reduces the risk by 43% of the infant having an acute otitis media in the first two years of life. (38)

Immune system

Another study has shown that the thymus, a vital organ for the infant’s immune system, has a bigger volume in relation to the volume of non-breastfed children. (39) Lodge et al, also found evidence that breast feed babies have a lower chance of suffering from asthma aged 5–18 years. However, one must say, that further research concerning breastfeeding and asthma is needed, since the impact between both still remains unclear. (40) (41) A study which was published in June 2015, by Amitay et al, showed that breastfeeding up to 6 months after birth may help to prevent childhood leukaemia. 18 studies have shown similar association with the decrease risk from 14–19 % . (42) Another study by Bener et al, published in 2008, showed that the risk of lymphoid malignancies in children was decreased the longer they were breastfed. (43)

Recommendation WHO

The World Health Organisation recommends, starting exclusive breastfeeding in the first hour after birth and continuing it up to the six months of life. Additionally breast feeding on demand, should be carried on until the age of two. Exclusive means, no other foods or liquids, including water. (44)

Additional Facts

Cost

Parents who breastfeed, can save over 1000–13000 € in the first year of the baby life, due to no additional milk formula costs.

Environment

Breast milk is a renewable natural resource, which produces no garbage, minimal greenhouse gases and a smaller water footprint formula feeds. (45)

Health System

Journal Paediatrics published an estimated 13 billion US dollar, which would be saved, in the health system, if 90% of the US babies would be exclusively breast fed for the first 6 month after birth. Since it would reduce hospitalization and medical costs through its benefits. In addition, it could prevent 911 deaths annually, from whom 95% would be infants. (46)

Sleep

Studies have shown that on average parents who breast-feed, sleep approximately 30 minutes more per night than parents who feeds formula. The exact reason for this still has to be researched. (47)

Food

Food flavours, which the mother consumes during pregnancy, are transmitted into the amniotic fluid, which is then swallowed by the baby in the womb. In addition, some flavours eaten by the mother, can change the flavour of their breast milk. The study concludes, that prenatal and post-natal exposure to flavours, transmitted through amniotic fluid or breast milk, increase the enjoyment of flavours when starting solid food weaning. (48)

Summary

Breast milk varies during lactation. It can change its composition during the day, during the lactation period, between mothers and within populations. One can divide lactation into five stages with each stage having its own hormonal composition, which in turn regulates milk production. Each stage can also be differentiated by the milk that is produced. The best outcome for mother and baby is achieved by breastfeeding a baby. Breastfeeding not only has positive effects for the baby but also for the mother. It contains components, which uniquely to this day, can only be found in breast milk. One can confidently say that breast milk offers the best nutrition for a baby and one should start exclusive breast-feeding within the first hours after birth until the age of six months. After that ‘on demand’ breastfeeding should be continued while starting solid foods.

Additional Sources