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Best feeding: Unraveling the mystery of breastmilk

New research shows breast milk contains unique patterns of molecules and stem cells that are tailor-made for an infant’s health.

"We think of breast milk as a food or even a liquid with an easy replacement. But it’s not. It’s similar to blood – it’s a living human tissue,” says environmental journalist and Huffington Post columnist Jennifer Grayson.

Scientists are only now beginning to unravel the complexities of breast milk – from the recent discovery of stem cells in milk to its influence on an infant’s gut and therefore future health.

These are things Grayson looks at in her book, Unlatched: The Evolution of Breastfeeding and the Making of a Controversy. “We love to have this debate in the media about whether the benefits of breastfeeding are all they’re cracked up to be. And whether maybe formula is really an equivalent. But we’re having this conversation in the absence of any real knowledge.” Because although the human genome was mapped more than 10 years ago, says Grayson, scientists still don’t know exactly what is in human breast milk.

What we do know is the important role human breast milk plays in shaping the microorganisms in an infant’s gut. About 150 or more different variations of complex sugar molecules called human milk oligosaccharides (HMO) have been identified in breast milk, and these feed the microorganisms in the gut, selectively encouraging the proliferation of certain species.

Says Grayson, “Every mother produces a unique pattern of these 150 or more oligosaccharides that’s tailored directly to her infant – it’s like a fingerprint. There is a lot of talk now about breastfeeding being personalised medicine and it really is – it’s just amazing.”

Breastfed babies have a lower risk of respiratory infections; allergies such as asthma, eczema and lactose intolerance; type 1 and 2 diabetes; atopic disease; gastroenteritis; coeliac disease; hypertension; otitis media; obesity; high blood pressure and cholesterol; and sudden infant death syndrome.

The World Health Organisation (WHO) estimates nearly half of diarrhoeal diseases and a third of respiratory infections in children in low- and middle-income countries could be prevented with increased rates of breastfeeding. The WHO also estimates increased breastfeeding would save the lives of 800,000 children, most under the age of six months, and US$300 billion each year.

Exclusive breastfeeding for the first six months of life, followed by the introduction of appropriate complementary foods, is also a significant factor for reducing the risk of childhood obesity, says the WHO.

Thousands of distinct protectors

The health and economic effects of human breast milk are hardly surprising given the complexity of this living tissue – it contains a vast array of complex nutrients and thousands of distinct bioactive molecules that protect against infection and inflammation and contribute to organ development, maturation of the immune system and creation of a healthy microbiome.

In 2015, scientists from the University of California published research on 524 newly discovered protein molecules in human breast milk, increasing the staggering total of identified protein molecules in the milk to more than 1600. Yet the purpose of many of these molecules is still unknown.

Meanwhile, the first reports of cells with stem-like properties in breast milk emerged only in 2007, with confirmation of breast-milk stem cells occurring within just the past five years. This discovery was met with excitement by large sectors of the scientific community, but more for the potential human breast milk may offer as a more ethical source of stem cells than ones from embryos, rather than their potential role in the development of infants.

Indeed, far less focus has been placed on understanding the role of stem cells or many of the other cells found in breast milk. A review in Nature, published last year, noted that “cells are not a negligible component of breast milk”, yet most research has focused on factors influencing the nutritional composition of breast milk. As a result, exactly what function the stem cells play is still unknown, as is the nature and function of thousands of other compounds in human breast milk.

Perhaps most surprising to our generation is the relatively recent discovery that breast milk contains millions of microorganisms, along with oligosaccharides that feed those microorganisms. These oligosaccharides are not an incidental component of breast milk; rather, they are the third most abundant component in human breast milk, suggesting they play a crucial role in our well-being.

Researchers from Imperial College London recently discovered that some women’s breast milk contains an HMO sugar molecule called lacto-n-difucohexaose I that may protect newborn babies from infection by the potentially life-threatening bacterium known as group B streptococcus, a common cause of meningitis in newborns and a leading cause of infection in the first three months of life.

HMOs feed friendly bacteria, encouraging them to thrive and out-compete any harmful bacteria in the infant’s gut. These sugars may also act as a decoy, fooling the bacteria into thinking they are a human cell that the bacteria then attempt to invade. However, once the bacteria latch onto the sugar, they are simply excreted from the body.

A University of Connecticut student feeds human embryonic stem cells. Photo/Getty Images

Messing with the formula

Although there is still much to learn about how each of these 150 or more HMOs influence an infant’s microflora and future health, some companies are already adding certain HMOs to infant formula milk in the absence of clear know­ledge about how they influence infants with vastly different genetics, says Grayson.

Formula manufacturers are clearly hopeful of replicating human breast milk. However, Imperial College London lead researcher Dr Nicholas Andreas cautions it will be difficult for infant formula to replicate the complex mixture of sugars found in breast milk. “These experimental formulas only contain a couple of these compounds, whereas human breast milk contains dozens of different types.

“Furthermore, the quantity of sugars produced by the mother changes as the baby ages, so that a newborn baby will receive a higher amount of sugars in the breast milk than a six-month-old.”

This is because breast milk is a dynamic, bioactive fluid that changes composition as the infant grows, varies within feeds and across the course of the day, and varies between mothers. And though many mothers would be unaware of the complexity of breast milk, many understand the importance of breastfeeding their child, if the high rates of breastfeeding initiation are any indication.

Still, although about 80% of women in the US start out breastfeeding, half give up or start supplementing with formula by three months. Similarly in New Zealand, almost 80% of babies born in 2014 were exclusively or fully breastfed at two weeks after birth. But by the three-month mark, that had dropped to 56%, according to Plunket NZ. By six months, just 25% of babies were exclusively or fully breastfed in accordance with WHO recommendations.

“It’s because of the utter lack of support in society,” says Grayson. “In the US, we have zero maternity leave – we’re one of a tiny handful of countries in the world, and the only developed nation, without maternity leave. We’ve been promoting ‘breast is best’ in an environment where it’s completely unfeasible for women to successfully breastfeed their babies. They have their babies and then they go back to work with a breast pump three weeks after giving birth.

“And we wonder why, at least in the US, we now have really high initiation rates but half of them give it up or start supplementing with formula after just a few weeks. It’s because it’s an impossible situation.”

New Zealand recently increased its maternity leave provision from 14 to 18 weeks’ paid leave, at a rate equivalent to about 48% of average previous earnings. That puts us on an equivalent footing to Australia but still well below the OECD average in 2015 of 54 weeks’ paid maternity leave. More importantly, it’s less than the 26 weeks the WHO recommends for ­exclusive breastfeeding.

The tricky part

Massey University nutrition lecturer Louise Brough says the lack of support for mothers once they return home from giving birth in hospital affects ongoing breastfeeding rates. “New Zealand has excellent initiation rates for breastfeeding during the first two weeks of life. However, after this there’s a steep decline.

“Breastfeeding isn’t easy. Many women need support with latching the baby on or positioning the infant to breastfeed successfully and without pain.” And though midwives provide excellent support, says Brough, they can’t be around 24 hours a day. She says more community-based support is needed to help mothers when they experience difficulties.

Says Grayson, “When a man has a problem with erectile dysfunction, he has an entire team of doctors at the Mayo Clinic, in the US, to help him. But when a woman has a problem breastfeeding, she gets a pat on the back and a can of formula.”

Grayson also believes the sexualisation of women’s breasts in Western culture has played a significant role. “When you look at two periods of time in history when breasts became sexualised, [the first] was 18th-century France, when all of a sudden women started outsourcing the nursing of their babies to wet nurses on a mass scale.”

The second time sexualisation occurred was from the 1940s and 1950s in the US, she says. “Breastfeeding declined basically from the turn of the last century through to the 1930s and 1940s. This was then followed by the rise of starlets such as Marilyn Monroe and big cone bras.” In both periods, the sexualisation and fascination with women’s breasts came after they were hidden from view – “they came to serve another purpose”.

Public outcry

Grayson says although we unfailingly promote the message that “breast is best”, we’re doing so in an environment that makes it almost difficult for many women to successfully breastfeed.

Women who breastfeed are still routinely asked to leave cafes, shops and public places in many countries, despite laws aimed at encouraging breastfeeding and protecting the ability to do so in public. And often this occurs to a chorus of approval from online commenters: “Another attention seeker. Why do they have to be so public about it?”

Until recently, Facebook has actively removed photos of breastfeeding mums that it said contravened its regulations, a surprising move, given the social media network permits videos and images of abuse, murders and terrorist activities. The sight of a woman breastfeeding, it seems, is more distressing to view than an image of a beheading.

Breast milk has been “pivotal to the survival of the human race for hundreds of thousands of years”, says Grayson, so “there must be something special about it. It’s amazing how easily we’ve forgotten that.”

This article was first published in the November 5, 2016 issue of the New Zealand Listener. Follow the Listener on Twitter, Facebook and sign up to the weekly newsletter.