The main hormone responsible for the production of breast milk is called 'prolactin'. Prolactin is produced by the woman's anterior pituitary gland in her brain. By the middle of pregnancy, prolactin levels are up to 20 times higher than they were before conception. However, despite these very high levels, the milk-producing cells in the woman's breasts do not respond (by producing mature milk) because of the high levels of progesterone hormone being produced by the placenta.
After the baby's birth, the placenta is delivered and the levels of progesterone decrease fairly rapidly over the following 48 to 72 hours (yet remain higher than they were before the pregnancy). About 2 to 5 days after the birth, the progesterone drops to a level where it can no longer inhibit the prolactin hormone. The high levels of prolactin are then able to stimulate the milk producing cells in the breasts to produce mature milk, being seen as the woman's milk 'coming in'.
Colostrum is the first fluid a woman's breasts produce and is present from about 16 to 24 weeks of the pregnancy, depending on the woman's individual body. Colostrum is a clear or creamy-yellow substance that is syrupy in consistency and is specially designed as the baby's first food once they are born.
Babies thrive on colostrum until their mother's mature milk comes in (sometime between days 2 to 5 after the birth). Colostrum contains more proteins, minerals and fat-soluble vitamins than mature milk (but less lactose, fats and water-soluble vitamins). It also contains more anti-infective agents (or 'antibodies'), that help protect babies until their own immune systems mature. Colostrum is lower in volume than mature milk, so it does not overfill your baby's very small stomach (about the size of a golf ball at birth!)
It is possible for some women to hand express colostrum from their nipples during the pregnancy, or to occasionally leak colostrum. This does not happen for every woman (and is no reflection on your ability to breastfeed). If you are leaking colostrum, you may choose to wear breast pads in your bra. For women who try to express colostrum, it is normal to only to get a few drops out at any one time. This can be done by massaging the breast down to the nipple and then compressing the areola, a couple of centimetres behind the nipple. Colostrum can also be expressed from the breasts of women and grandmothers years after they stop breastfeeding!
It is normal for some women to notice a small amount of blood mixed with the colostrum that may come away during pregnancy. This comes from within the breast and is caused by the rapid growth of blood vessels in the growing ductal system, in preparation for breastfeeding. Also, drops of blood may also be seen on the bra because the sticky colostrum temporarily 'glues' the nipple to the inside of the bra and a tiny bit of nipple skin is removed with the bra, which does heal.
Mature breast milk is capable of being produced from about 24 weeks of pregnancy. Women who have their babies prematurely after this time should be able to produce and/or express breast milk for their baby. Mature breast milk starts to be produced about 2 to 5 days after the baby is born and fully matures about 2 weeks after the birth.
Mature human breast milk is 80% water and contains whey proteins, carbohydrates (mainly lactose), fats, minerals, vitamins, enzymes, hormones, anti-infective and anti-allergenic agents. It is the last 4 ingredients that cannot be reproduced in artificial formula milk. The milk of all mammals contains similar essential ingredients, but in different combinations and quantities to uniquely suit the species.
It has only been in the last few decades that the complexity of breast milk has been truly realised. For example, it is now known that human milk has a finely balanced combination of amino acids (or the 'building blocks' of protein). This combination is unique to human milk when compared to the milk of all other animals (including cows). Therefore, it is not the amount of protein in the milk that is important, but the type of protein and the finely balanced combination of different amino acids, (such as glutamic acid and taurine) that enable the baby to digest and absorb fats in their intestines in the first few weeks of life. The combination of ingredients in breast milk actually changes and matures as the baby grows older, to specifically suit your baby's changing needs.
The following is a brief summary of the amazing ingredients that make up breast milk:
Protein. Protein is responsible for the body's metabolism and the growth and development of body cells and tissues. The main type of protein in human breast milk is lactalbumin (or whey protein) with small amounts of casein. Casein is responsible for carrying calcium and phosphate minerals in the milk. The amount of protein in breast milk is relatively lower than in many other milks and it is designed in a way that the baby's stomach can digest it very quickly.
Carbohydrates. Carbohydrates are responsible for energy and calories and is important for brain growth and development. The main carbohydrate in human milk is lactose (having about twice as much as cow's milk). Lactose also has essential lactobacillus micro-organisms in it (not present in formula), helping the baby to be more resistant to bowel infections, diarrhoea and thrush.
Fats. Fats (or lipids) are essential for energy and calories, development of the brain, nerves and blood vessels. Fats available in breast milk are mainly globules of triglycerides, designed to be easily absorbed and digested by the baby. Arachidonic acid, docosahexaenoic acid and linoleic acid are found in high quantities in breast milk. These fats mature the cells of the baby's intestines, aid digestion and add to the anti-infective protection of the breast milk. Fat contents and mixtures vary with each feed, and the duration of the feed. The fat content of hind milk is highest in the afternoons and lowest in the mornings and increases with the duration of each feed.
Minerals. Minerals present in breast milk include calcium, phosphorus and magnesium. These are important for bone growth and muscle functioning. Breast milk has only minute quantities of salt. Breastfed babies tend to have higher blood levels of calcium than formula fed babies, because breast milk has exactly the right mix of special fats and vitamin D to enhance the absorption of these minerals. Small amounts of zinc, iron and selenium are also present in breast milk.
Vitamins. Water soluble vitamins B and C are concentrated more in the fore milk (or the milk at the beginning of a feed) and fat soluble vitamins such as A, D E and K are more concentrated in the hind milk (or towards the end of the feed).
Enzymes. There are 3 enzymes present in breast milk. They include lysozyme (an ant-bacterial enzyme), lipase (which aids fat digestion) and amylase (which digests carbohydrates). Amylase is usually high in human saliva. As newborn babies have a lack of saliva for the first 12 weeks or so, the amylase in breast milk compensates for this to help milk digestion. These are not present in formula milk.
Hormones. The hormones present in breast milk include prolactin, prostaglandins, insulin, thyroid stimulating hormone, thyroxine and growth hormone. These aid the baby's growth and development and are not present in formula milk.
Anti-infective agents. There are many anti-infective agents present in breast milk. These include leucocytes that are capable of surrounding and destroying bacteria and immunoglobulins from the mother's immunity (called IgA, IgG, IgM and IgD). They help protect the baby against infections in the first months of their life, particularly protecting the lining of their intestine. Lactoferrin increases the baby's absorption of iron from the milk and reduces the growth of the bacteria 'E. coli' in the bowel.
Anti-allergenic agents. Babies who are exclusively breastfed for the first 6 months of their life have less chance of developing food allergies, skin disorders (such as eczema) and allergic breathing disorders, (such as asthma).
And all this is only what we've discovered to date!
Last revised: Wednesday, 19 December 2012
This article contains general information only and is not intended to replace advice from a qualified health professional.