Mother’s milk is a marvel. It is an extraordinarily complex fluid, assembled in the mother’s body through a long series of interconnected steps. Breast milk is also uniquely adapted to the changing nutritional needs of a baby. At birth, breast milk is perfectly suited for the infant’s vulnerable immune system and immature digestive tract. As the baby develops, the composition of breast milk and its proportions of fat, protein, and carbohydrates change accordingly to fuel growth and development.
“Mother’s milk is nutritionally complete to meet all the needs of the baby,” says Deepak Chopra. “But it’s not just the nutrition that comes from the milk that supports a healthy baby. It’s also everything else that’s happening between the mother and baby: a whole range of experiences that also nourish the baby, through touch, through smell, through sensual delight. It creates pleasure, but also increases trust and the bond of love and a deeper understanding between the baby and the mother.”
The two main hormones of lactation in humans are prolactin (from the Greek “to urge on”), which plays a wide range of physiological roles in many different animals, and oxytocin (Greek for “swift birth”), which is unique to mammals and plays a key role in initiating delivery. Oxytocin is also involved, writes Sarah Blaffer Hrdy, in “the rush of warm sensations that suffuse a mother when she breastfeeds, the tapering off of inhibitions as two mammals sit companionably side by side, or groom each other, or when longtime mates nuzzle or rub each other. Oxytocin levels go up whenever a person undergoes a good massage.”
When a woman breastfeeds, the baby’s sucking stimulates nerves in her nipple. These nerves carry a message to the mother’s brain and oxytocin is released. “It signals to the brain,” explains Sharon Donovan, Professor of Nutrition and Pediatrics at the University of Illinois, “‘OK, I need the milk down here now.’” Oxytocin is then released by the pituitary gland and flows through the bloodstream to the breasts, where it causes specialized cells surrounding the tiny sac-like alveoli to squeeze milk out and into the milk ducts.
So powerful, in fact, is the link between oxytocin and milk production that its influence can be triggered by emotions, conscious thought, or even sensory experience. “A mother could be having loving feelings about her baby, or she could be thinking about her baby or she could hear her baby cry, and she’ll have milk let-down, because these stimuli can cause oxytocin to be released,” explains Chopra. (Another example of the powerful influence of milk-production hormones can be seen in the small percentage of newborns that secrete fluid from their own nipples, a phenomenon called galactorrhea. Some cultures refer to this temporary flow as witches’ milk.)
Breast milk’s initial function is to transfer immune factors to the newborn. In the first couple of days after a baby is born, a mother produces a yellowish liquid called colostrum. Compared to mature milk, colostrum is lower in fat, carbohydrates, and calories, but is very high in infection-fighting antibodies and white blood cells. In terms of volume, the mother produces very little colostrum, literally only tablespoons, and yet it plays a key role in helping to develop baby’s immune and digestive systems. Colostrum’s mild laxative effect may also help newborns pass their first bowel movement, which usually happens within 12-24 hours after birth. Called meconium, this initial stool is a thick, sticky, greenish-black substance made of mucus, bile, amniotic fluid, and shed cells.
Milk production is a physiological compromise between the resources of the mother and the needs of the infant. Lactation is so critically important that nature has made it a very robust and resilient biological process. How else would humankind have survived through lean times? In times of scarcity, however, a mother’s body will tap her own stores of fat and nutrients for the benefit of her infant: the baby’s nutritional needs have priority. It’s a fine balance, of course, since the well-being of the infant is clearly dependent on the well-being of the mother.
Not every mother can breastfeed or chooses to do so. And even most who do will also supplement with formula. It is important for mothers to realize, then, that oxytocin, as well as the bonding it helps to enhance, is not restricted to breastfeeding. Oxytocin is a mammalian hormone present in both males and females that plays a role in calmness and contentment in many different contexts.