Why is colostrum so important?

Colostrum, the first milk you produce when starting breastfeeding, is the ideal nourishment for a newborn. It’s highly concentrated, full of protein and nutrient-dense – so a little goes a long way in your baby’s tiny tummy. It’s also low in fat, easy to digest, and brimming with components that start his development in the best possible way. And, perhaps even more importantly, it plays a crucial role in building his immune system.

Colostrum looks thicker and more yellow than mature milk. Its composition is different too, because it’s tailored to your newborn’s specific needs.

Colostrum fights infection

Up to two-thirds of the cells in colostrum are white blood cells that guard against infections, as well as helping your baby start fighting infections for himself.¹ “White blood cells are important as far as immune responses are concerned. They provide protection and challenge pathogens,” explains Professor Peter Hartmann, a leading expert in the science of lactation, based at The University of Western Australia.

Having left the protection of your body, your baby needs to be ready for new challenges in the world around him. The white blood cells in colostrum produce antibodies that can neutralise bacteria or viruses. These antibodies are particularly effective against tummy upsets and diarrhoea – important for young babies who have immature guts.

It supports your baby’s immune system and gut function

Your colostrum is especially rich in a crucial antibody called sIgA. This protects your baby against disease, not by passing into his bloodstream, but by lining his gastrointestinal tract.² “Molecules that have provided an immune defence against infection in the mother are transported in her blood to the breast, join together to form sIgA, and are secreted into her colostrum,” explains Professor Hartmann. “This sIgA becomes concentrated in the mucus lining of the baby’s gut and respiratory system, protecting him against illnesses the mother has already experienced.”

Colostrum is also rich in other immunologic components and growth factors that stimulate growth of protective mucus membranes in your baby’s intestines. And while that’s happening, the prebiotics in colostrum feed and build up the ‘good’ bacteria in your baby’s gut.³

Colostrum helps prevent jaundice

As well as protecting against tummy upsets, colostrum acts like a laxative that makes your newborn poo frequently. This helps empty his bowels of everything he ingested while in the womb, in the form of meconium – dark, sticky stools.

Frequent pooing also reduces an infant’s risk of newborn jaundice. Your baby is born with high levels of red blood cells, which take oxygen around his body. When these cells break down, his liver helps to process them, creating a by-product called bilirubin. If your baby’s liver isn’t developed enough to process the bilirubin, it builds up in his system, causing jaundice.⁴ The laxative properties of colostrum help your baby flush out bilirubin in his poo.

Vitamins and minerals in colostrum

It’s the carotenoids and vitamin A in colostrum that give it the distinctive yellowy colour.⁵ Vitamin A is important for your baby’s vision (vitamin A deficiency is a major cause of blindness worldwide),⁶ as well as keeping his skin and immune system healthy.⁷ Babies are usually born with low reserves of vitamin A,⁸ so colostrum helps make up the deficit.

“Those first three days or so are a crucial time for establishing breastfeeding”

Colostrum is rich in minerals too, such as magnesium, which supports your baby’s heart and bones; and copper and zinc, which help develop his immune system.^9,10 Zinc also aids brain development, and there’s nearly four times more zinc in colostrum than in mature milk¹⁰ to support your newborn’s rapidly developing brain.

Colostrum helps your baby grow and develop

Your colostrum contains numerous other components that support your baby’s growth and development. Scientists are still working out the part some of them play.

“Colostrum maintains the same composition until about 30 hours after birth,” says Professor Hartmann. “It’s relatively high in protein because all the antibodies in it are proteins. It’s relatively low in lactose [the milk sugar], and the fat is a different composition to that in mature milk.” 

And because colostrum has a similar make-up to amniotic fluid (which your baby has been swallowing and excreting in your womb), it’s ideal easing for his transition to the outside world.¹¹

The transition from colostrum to mature milk

After two to four days, your breast milk should ‘come in’. You’ll notice your breasts feeling firmer and fuller, and instead of colostrum they’ll produce transitional milk, which is whiter in colour and creamier in texture.

“Those first three days or so are a crucial time for establishing breastfeeding,” says Professor Hartmann. “If you can get things right during this time, you’re likely to get good lactation and the baby growing well.”

It seems unimaginable now, but in just one year your baby could be walking and on the verge of talking. You only produce colostrum for a short time, but it makes an invaluable contribution to those first 12 months, and to the rest of his life.

Interested in finding out more? Read our free ebook The Amazing Science of Mother’s Milk and see our article What is transitional milk?