(9 pm. – promoted by ek hornbeck)
This is the forth and final installment on my short piece about milk. This time, instead to focusing on human consumption of milk from other species, in particular from cattle, to the importance of human infants being given human milk until at least six months of age. The first three installments can be found here, here, and here.
Human milk was universally used up until comparatively recently as the sole food for infants. However, it was not always the mum of the child that supplied the milk. Throughout history, surrogate women have supplied milk for other women’s children, a practice know as wet nursing. This was pretty much confined to the wealthy class when the mum chose not to breastfeed her child and either hired other women to feed them or made slaves to that. Although not explicitly said, the Mammy character in the book and motion picture was assumed to be Scarlett’s wet nurse. In other cases friends of relatives of women who for some reason or another could not nurse a baby would fill in for her. More on that later.
In the 1950s many countries began to encourage the use of infant formula as the “scientific” successor to natural breast milk. While formula can be a wise choice in many circumstances, the latest research is pretty much a consensus that natural breast milk is superior in almost all ways to formula. More on that later as well.
All mammals produce milk. Well, at least the females do, or can. That is one of the things that have caused mammals to be quite dominant in evolutionary terms. However, it comes with costs. With few exceptions, vertebrates and non vertebrate animals pretty much abandon their offspring at birth, or even before. Mammals are sort of special in that mammalian offspring are completely dependent on the mums for a period of time to give them food. Birds are sort of intermediate because, like mammals, their offspring are born sort of helpless. But birds do not produce proper milk. Usually then just bring food that they hunt back to their offspring. Mammals manufacture it themselves.
I think that I shall skip the evolutionary history regarding milk production. I started to go into it, but that would take up 3000 words that are better spent in describing why human infants do better with breast milk, and that is the important thing. It is sort of difficult to describe, but here goes a stab at how milk is produced. It is as apt for any mammal is it is for humans. I shall concentrate on human lactation, but it is pretty much the same for most mammals.
In humans, around the 24th week, hormones are released from the placenta and the pituitary gland that have profound effects on the breasts. One of the most important, progesterone, “primes” the breasts to expand the aveoli, the milk producing microstructures. They are not producing milk at the time, but this is why the breasts get larger around that time. I think that the comic Robin Williams called this the phenomenon “The Titty Fairy Visiting”. Here is an embed to the routine:
It remains at high levels in the blood until delivery. Oddly, although it stimulates the growth of the microstructures, it also inhibits milk production. It could be likened to a work crew building new plumbing with the foreman making sure that the water was not turned on until the work was finished.
Around the same time, estrogen is coming to high levels. It works with progesterone in causing fine structure in the microstructures that will produce milk to get organized. Also like progesterone, it inhibits the secretion of milk. Think of estrogen as the supervisors in the aforementioned scenario that take specialized work crews to make sure that the detail work was done, and who also makes sure that the water inlet is still not open until the crew is finished.
Simultaneously, prolactin level start to rise. This hormone directly stimulates the production of milk, but is held in check by progesterone. Going back to the work crew, prolactin turns on the main water supply, but progesterone keeps the taps pretty much closed. It is this interaction that cause the breasts to become quite large, and sometimes painful, late in pregnancy. More Titty Fairy stuff, I suppose. It also stimulates the production of the brown pigment melanin, that often makes mums have sort of dark areolae. That pigmentation often passes later in most cases, but often the areolae are never quite as pale as before the first pregnancy. This does not seem to be cumulative, so second and third pregnancies do not change the color very much.
The bottom line is that the Tittie Fairy generally comes to visit around the fifth or sixth month of pregnancy, and while the male generally is delighted with the visit, the female usually wishes that the fairy would wait a while because of discomfort.
What we have discussed so far is referred to Phase I of Lactogenesis. Very often a woman will leak fluid during this phase, and this is dilute colostrum. We shall have more on that in a bit.
Phase II begins after birth upon the ejection of the placenta. In addition to being the interface betwixt the mum and the fetus during pregnancy, it is also an organ in its own right that secretes lots of progesterone, amongst other hormones. Remember, progesterone inhibits milk secretion, and with placental progesterone now no longer being produced, milk secretion commences within hours. The first milk produced is colostrum, as mentioned before. It is critical importance to the health of an infant.
Colostrum is not like milk that is produced later. As a matter of fact, it could be argued that it is not really milk at all, but rather a concentrated essence of life for the newborn. Remember, a newborn’s digestive system is very small, and can not absorb much volume at a time. It is much higher in protein than later milk, contains lots of live white blood cells, growth promoters, and several immune fractions of the mum’s blood. Because the newborn’s digestive system is not yet fully functional, these components are absorbed through the stomach and intestines, doing all kinds of important things that formula just can never do. Colostrum is produced for five of six days, sometimes seven, and then actual milk is produced.
Women choose to breastfeed or not for many reasons, and I respect their choice. However, even if a new mum decides not to breastfeed on a long term basis, my considered opinion is that depriving a newborn of colostrum borders on child abuse. Formula does a good enough job replacing regular milk, but does not have the growth factors, the high protein levels, and especially the immune components that colostrum has. I strongly advise mums of newborns to nurse them for the first week, even if they do not plan to breastfeed for the long term. I feel quite strongly about this, and with good reason.
During Phase II, stimulation of the nipples either by the infant or a pump causes prolactin levels to increase, and that in turn causes milk to be released. Interestingly, it might be that increased prolactin levels may be associated with postpartum depression, because in the central nervous system prolactin in antagonistic to dopamine, the neurotransmitter that elevates mood. This is sort of speculative, and since prolactin levels are already elevated during Phase II whether or not an mum breastfeeds, there is little concern that breastfeeding causes postpartum depression. Interestingly, sexual climax also causes prolactin levels to increase in females and vasopressin levels to increase in males, and it is thought that this release contributes to the refractory period, where sexual desire has been sated so that excitement turns to what many refer to as “glowing”. But I digress here.
Phase II lasts, depending on the mum and newborn, for a couple of weeks or longer. Actually, there is no abrupt transition from Phase II to Phase III, but rather a gradual one. As lactogenesis proceeds, the colostrum is gradually replaced by “real” milk, and the infant’s digestive system begins to develop to handle the new nutrients in real milk. In the mum, the transition has to do with the hard wired endocrine hormonal feedback loop in Phases I and II to a more localized, breast centered control mechanism. Since the breasts have been prepared by the complex hormonal changes in the first two phases, they are by this time milk producing factories, as it were, and with continuous maintenance can produce milk for months or even years after no other trace of pregnancy or postpartum hormonal upsets remain.
There is a bit of controversy about this, but it is mainly anecdotal. There seems that there might be some connexion betwixt breastfeeding and avoidance of pregnancy, but the data are pretty thin. Breastfeeding is NOT a valid method of contraception, but the legend persists that women who are nursing will not get pregnant. That is just wrong, because even though they continue to lactate, for the most part after only a few weeks their hormone balance returns to the nonpregnant state, complete with menses.
In Phase III, the feedback loop is not a central endocrine one (during Phase II, pregnancy is very unlikely) but as mentioned before, more of a local feedback loop. The already primed breasts are ready to make milk, and will do so as long as milk is taken from them. As a matter of fact, the more milk that is removed, the more that is produced. That is why wet nurses were able to provide milk for not only their own children, but for their surrogate children. At the risk of being crude, and I certainly do not mean this as any sort of an insult to breastfeeding mums, we use that phenomenon all of the time in the dairy industry, stripping essentially all of the milk from cows to keep production high.
Thus, if a new mum desires to breastfeed for the long term, it is essential that the milk be removed often and completely. That does not have to be done by the infant, and there are often difficulties with breastfeeding that have to do with a number of things, like the infant not having a strong “latching” reflex where he or she does not attach firmly enough to the nipple to suckle properly, to inverted nipples for the mum (not as common as thought), to the nipples being to large for the infant to get her or his mouth around properly. Fortunately, manual expression or higher tech breast pumps can keep milk production going and the milk thus obtained can be put in bottles and fed to the infant with artificial nipples that fit her or his mouth better. This rarely has to be done for more than a couple of weeks, because as the child grows the latching reflex becomes a learnt behavior, and the mouth also gets bigger. I urge women who want to breastfeed long term to use these methods if initial breastfeeding attempts are not very successful, because as Phase II grades into Phase III, if not enough milk is removed from the breasts the milk producing feedback loop will rapidly deteriorate to the point that it will not be possible to produce milk. Even if it has to be discarded, it is essential to keep the flow going or it will stop.
It is possible to go directly the Phase III lactogenesis without Phases I and II. I observed this personally when the former Mrs. Translator and I adopted a kitten that was really to young to be weaned. The former Mrs. Translator has a older cockapoo dog that had never had puppies who had a wonderful disposition, and that kitten would try to nurse. Cuddles would lie still for him, and in just a few days she was producing milk. This can also occur in humans, and some couples do so for nothing but fun.
I realize that this has been fairly graphic, but it is important. It is not my personal view that breastfeeding infants is by far the best for them, but for the mum as well. I mentioned that there is a strong statistical link indicating that women who breastfeed have a lower incidence of breast cancer later in life. But there is more.
There is a psychological bond that forms betwixt the infant and the mum when infants are breastfed. I am doing some armchair coaching now, but I believe that these observations are correct.
First, think about the life experience of the fetus up to the time of birth. No light, but lots of sound. The sound of the mum’s heart. Remember, water conducts sound much better than air, so the fetus hears her or his mum’s heart beating, and also her breathing. When placed on the breast, the infant can hear the mum’s heart beating, and can feel the rhythmic rise and fall of her chest as she breathes.
Some of the oldest primate research about socialization has to do with infants being touched. Without going into the details, it turns out that infant primates that are removed from any contact with others develop antisocial behavior, and to use the vernacular, actually become quite mad in the absence of touch. What better form of touch in an infant is there than to be cradled in the arms of a mum and held to the breast?
OK, let us get back to technical issues. What if, for either medical issues or personal choices, a mum can or will not breastfeed? There are some good alternatives, with the glaring exception of colostrum as described earlier. There is just no substitute for that.
For infants, cow’s milk is right out. So is goat’s milk and sheep’s milk. There are reasons for that. The primary reason is that those animals grow and develop much more rapidly than humans do, at least with muscles and bone. Human infants are quite different, because in their first few weeks and months their brains take precedence over skeletal and muscle development. After a couple of days, baby ruminants are walking and even running with their mums, but you will have to admit that none of these ever get very bright. With humans, it is quite the opposite. Infants stay infants in the physical sense for a LONG time, but their brains are developing at the expense of muscles and bones. That is not to say that as an infant human grows that bones and muscles are not developing, but that orange sized organ, the brain, is getting the lion’s share of nutrients. Here is a rough comparison of cow’s milk and human milk. I shall point out significant differences. The human milk value is first, then comments if any. All values, unless otherwise specified, are in grams per 100 mL.
Fat: 4.2 3.25 Polyunsaturated 14% 0.2%
Here is a significant difference. The fat content of human milk is somewhat higher than that of cow’s milk, but that that different. The big difference is that human milk contains much, more polyunsaturated fat than cow’s milk, and that is directly linked to brain development.
Protein 1.1 3.22
This is a huge difference, almost a factor of three. Muscle development, highly dependent of protein content, is important for cattle, but brain development, depending on, amongst other things, polyunsaturated fat content, is more important for humans.
Carbohydrate (mostly lactose) 7.5 5.26
Human milk contains more carbohydrate, and the 0.5 gram out of the 7.5 per 100 grams are complex ones. Cow’s milk contains just about only lactose. It is thought that the complex carbohydrates in human milk are also important for brain development.
Now it gets really interesting. The mineral content is quite different betwixt human milk and cow’s milk. Check this:
Calcium 0.03 0.113
While cattle are forming bones, with almost four times the calcium in cow’s milk than in human milk, humans are forming brains.
Sodium 0.015 0.043
Cow’s milk has almost four times the amount of sodium than human milk. Sodium is important for brain formation, but is essential for fast reaction neurons that involve running. Herd animals need to run, humans need to make brains.
Potassium 0.055 0.143
Again, potassium is important for fast muscle neurons. There is over 2.5 times more potassium in cow’s milk than in human milk.
The bottom line is that cow’s milk is essentially poison for infants, at least until their digestive and excretory systems develop enough to handle it. It also does not contribute essential components for brain development. Cow’s milk is great for calves, but completely unsuited for human infants. Their kidneys can not handle the mineral load, and an infant fed on cow’s milk will almost surely die or have severe brain development issues.
Modern infant formula is more like human milk in its composition, and is fine to give to infants (after the colostrum phase) in place of actual milk. However, I still think that it is much less perfect than natural breast milk. On the other hand, I do not think that mums should feel guilty for using formula after the colostrum phase of breastfeeding is done.
A very interesting thing about milk is that its composition varies depending on whether it is the first milk given during nursing or near the end of nursing. The figures cited are average ones, but the fact is that the milk produced earlier is higher in carbohydrates and water and low in fat compared to the milk that is given near the end of a feeding session when the breast is becoming relatively empty. That last milk is very creamy and high in fat compared to the early milk. I am not sure if this is accidental or if there is an evolutionary advantage. However, I believe that this speculation fits well with observations:
Infants have low stores of nutrients compared with older children, and also low stores of water. It seems to me that with the relatively watery, sugary early milk there is a thirst quenching component as well as an initial infusion of sugar, which is the basic fuel for metabolism and is not stored and released as glycogen as in older children and adults, gives the infant what he or she needs after what is essentially a fast. This gets them hydrated and the metabolism revved, and then the fattier portion (fats are metabolized much more slowly than sugar) can be used more effectively because the immediate needs have been met. This is only an hypothesis on my part, but it makes sense to me.
As many benefits as breastfeeding has, there are some situations where it should not be done. Most importantly, it when the mum is taking drugs (either medically or recreationally) that pass from the blood into the milk. Since there are many different situations, each mum should consult with a physician for her particular case. Another rare situation occurs in the Inuit whose diet is almost exclusively meat and fish derived from the ocean. It is a dirty little secret that these fish, seals, and whales bioaccumulate large amounts of polychloronated biphenyls (PCBs) in their fatty tissues, and when eaten the PCBs are concentrated in milk because it is relatively high in fat. In those cases, it is possible for the mum to pass dangerous concentrations of those pollutants to the infant. This is, however, very much the exception rather than the rule.
There is controversy about how long breastfeeding should continue. The WHO recommend that infants be exclusively breast fed for the first six months, with other foods being slowly introduced at time. As I said earlier, the first week is critical, but six months seems a bit too short a period. However, the average age for the first central incisors to erupt (generally the lower two) occurs at about six months, and the upper ones two months later. The upper and lower lateral incisors erupt at about ten months, but of course there is a period of time betwixt eruption and full dentition of those. This indicates that about a year might be a reasonable cut off point for weaning. However, this is highly variable depending on the mum and infant, cultural influences, and many other factors. In some cultures children are breast fed until they are well past five years old, but there is no good science to support such a long period. I agree that six months is a reasonable minimum, and about a year a reasonable maximum.
This is only a very brief overview about breast milk and its importance, but I thought it a fitting way to end the series on milk. For all mammals, natural milk of the same species is the ideal food for infants, with milk from other species being toxic. Modern formula is an acceptable substitute for milk after the colostrum phase, but is still not as good as natural milk. Fortunately, western culture is catching on to these facts and in relative numbers, more women breastfeed now than they did even as late as the 1960s.
Well, you have done it again! You have wasted many more perfectly good einsteins of photons reading this sticky piece. And even though Mitt Romney realizes that his tax “plan” would be a disaster when he reads me say it, I always learn much more than I could possibly hope to teach my writing this series, so keep those comments, questions, corrections, and other feedback coming. Tips and recs are also very welcome. I shall stick around tonight as long as comments warrant, and shall return around 9:00 PM tomorrow for Review Time.
Doc, aka Dr. David W. Smith
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