Breastfeeding has many benefits, but some campaigners argue that health policies to encourage the practice could be placing potentially harmful pressures on mothers. Clare Wilson looks at what the evidence says.

As the birth of her first baby drew near, Suzanne Barston was determined to do everything right – including how she fed him. “I really wanted to breastfeed,” says the writer, who lives near Chicago. “I had gone to all the breastfeeding classes.”

But within a couple of days, it was clear her baby was unable to suck from the breast properly, so she began pumping her breastmilk and giving it from a bottle for every feed.

Doing this took up to several hours a day, leaving her almost no time to look after herself. As the weeks went by, the constant pumping and feeding left her mentally and physically exhausted, contributing to her growing post-natal depression. Her son wasn’t thriving either; he developed a rash and often had blood in his bowel movements. A doctor said he could be allergic to something in her diet that was passing through to the milk and suggested they try a hypoallergenic brand of formula.

Within two days, her son’s symptoms disappeared, and once they stayed with the formula he made a full recovery. It sounds like a happy ending, but looking back, Barston is angry about how much pressure she was put under to breastfeed, when, as she now sees it, “It’s not that big a deal.”

Breastfeeding not a big deal? That sounds like heresy. “Breast is best” is the advice from the World Health Organization, Unicef and countless other respected health bodies, who say babies should be fed exclusively with breastmilk for the first six months of their life because of the health advantages to both children and their mums. It’s thought to be so beneficial that women are now encouraged to keep nursing into toddlerhood and beyond.

The biggest concern, they argue, should not be whether the baby is given breastmilk or formula, but whether they are getting enough nutrition full stop

Yet the idea that mothers should breastfeed at all costs is now being challenged by a small but increasingly vocal group of campaigners, including parents such as Barston, and even some doctors and researchers. They argue that if a new mum struggles to breastfeed, pressure to persevere can lead to intolerable strain. What’s more, some women are physically unable to make enough milk and if this goes unnoticed their babies can get dehydrated, occasionally even to the point of brain damage. The biggest concern, they argue, should not be whether the baby is given breastmilk or formula, but whether they are getting enough nutrition full stop. In other words, “fed is best”.

“People talk a lot about the benefits of breastfeeding – fine, but talk about the risks, too, and let women make their own decision,” says Amy Tuteur, a former US obstetrician, who has written a critical book about the natural parenting movement, called Push Back.

So what does the evidence actually say?

Official attitudes to breastfeeding today are very different from the way it was viewed in the past. As formula use grew in the first half of the 20th Century, firms began advertising their products as superior to breast milk. Healthcare staff would often discourage women from breastfeeding, seeing it as old-fashioned or lower-class.

That seems shocking now we know that breastmilk contains countless beneficial substances, such as antibodies that kill germs. The milk’s composition also changes day-to-day to meet the baby’s needs, and even over a single feed – it’s more watery at first, for instance, to quench the baby’s thirst.

In developing countries, there’s another concern. Formula milk is usually bought as powder that’s mixed with water and poor people may not have access to clean water or fuel for boiling it.

From the 1970s onwards, outrage over formula advertising in the developing world grew, leading some to boycott baby milk manufacturer Nestle, for instance. Now many countries ban such adverts and as interest has grown in the potential public health benefits of breastfeeding, healthcare staff have become increasingly vocal about them to new parents.

Barston, for instance, felt that she was judged harshly for not breastfeeding, despite her struggles.  She has launched a blog to support other mums in her position, called “Fearless Formula Feeder” and she estimates that more than half who comment on it have also had post-natal depression partly caused by pressure to breastfeed.

I hear a lot of horror stories. Some women are near suicidal - Suzanne Barston

Of course, some women really enjoy breastfeeding. But others find it amplifies the toughest aspects of new parenthood – the lack of time to yourself, the sleep deprivation. In theory a partner can do some feeds with pumped breast milk, but not all women can express their milk this way, and some breastfed babies refuse the bottle point blank – so the feeding burden falls entirely on the mum. “There’s good evidence that being exhausted can lead to poor mental health,” says Barston. “I hear a lot of horror stories. Some women are near suicidal.”

As well as those who find it a mental struggle, some can’t physically make enough milk. Women are generally told this is rare – for instance, an NHS website says “almost all women are physically able to breastfeed”. But as many as one in seven new mums can’t make enough milk, according to one study by Marianne Neifert at St Lukes Hospital in Denver, Colorado.

Even outside of this group, most women find it takes several days after the birth before they start making much milk. In the meantime, some babies end up dehydrated or they develop jaundice, which is a side-effect of not getting enough milk and needs treatment in hospital. Sasha Howard, a paediatrician at Barts Health in London, has seen many cases of dehydration caused by exclusive breastfeeding. “Some babies need some formula from a bottle or a nasogastric tube. Some who are really unwell need an intravenous drip.” In some rare cases, dehydration has even led to brain damage and death.

Ten years ago if breastfeeding wasn’t going well, healthcare staff would have been more likely to intervene earlier by suggesting a bottle. But health guidelines in many countries may now discourage staff from doing so – especially at hospitals that follow rules set by Unicef to encourage breastfeeding, known as the Baby Friendly Initiative. Now postnatal wards following these rules may keep their formula in locked cupboards – as if it’s a potential drug of abuse like morphine – or require a doctor’s prescription.

“This isn’t about harassing mothers or making them feel guilty,” says Trish MacEnroe, executive director of Baby-Friendly USA. She points out that hospitals used to whisk babies away the minute they were born and give them a bottle whether their mums wanted it or not. Their aim is to stop such practices. “First and foremost the initiative is to change these long-standing practices that really sabotage breastfeeding.”

If a mum starts using formula regularly, the baby sucks for less time at the breasts, which then naturally make less milk. This can be self-perpetuating, leading to her milk supply dwindling, says MacEnroe – and that would mean the baby loses out on a host of health benefits. After all, countless studies have found that breastfeeding cuts children’s risks of infections and allergies, and in later life keeps them healthier, slimmer – even more intelligent.

There are two problems with that argument, though. One is that the risks of formula jeopardising breastfeeding are unclear. Certainly milk supply dwindles if formula is given in ever-increasing amounts. But Howard is sceptical that giving one or two feeds a day from the bottle, for instance, inevitably causes supply problems. She points out that lots of women successfully mix breast and formula feeding for many months. “For some, a combination can be best.”

Then there is also doubt over whether the health benefits of breastfeeding are really as great as claimed. The vast majority of the studies to show these benefits are not the best kind of medical evidence, in other words randomised trials. That’s the way we test whether new medicines work, randomly allocating half the people in a study to get the new drug, and the rest to get the standard treatment, or a dummy pill, and then comparing the health outcomes of both groups.

Such a trial would be impossible to do with breastfeeding, because few mums would cede control over such a personal decision. Instead we can only observe how they choose to feed their babies, and assess the outcomes afterwards.

These observational studies do indeed find correlations between breastfeeding and better health. But correlations are notoriously deceptive. For instance, owning running trainers probably correlates with physical fitness but it doesn’t mean the trainers make you fit; a third factor – running - causes both.

With breastfeeding, possible third factors are income and education levels. Breastfeeding is more common among higher-income families these days, partly because they tend to follow health advice, and partly because the mums can afford to take a longer maternity leave. And better-off people enjoy better health for a host of reasons unrelated to breastfeeding, such as smoking and drinking less. So it’s unsurprising that breastfed babies grow up to be healthier – it’s like a badge of being middle class.

When you compare siblings within the same family, most of the long-term benefits of breastfeeding melt away

Scientists conducting these observational studies can tweak their results to try to account for the influence of income and education – but it’s hard to do so completely. And the studies that are the most rigorous about doing so tend to find the smallest effects from breastfeeding – as even a report by the WHO acknowledges. In a US study that got around the problem by comparing breastfed to bottle-fed siblings within the same family, most of the long-term benefits to health melted away.

Not all the claimed benefits are invalid. Premature babies given breastmilk are less likely to develop gut problems and severe infections like sepsis. In the developing world, breastfeeding avoids the risk of formula being made up with contaminated water.

Even in the West, the reduced risk of infections in the first year of life does seem to hold up in good-quality studies; breastfed babies are less likely to catch colds and diarrhoea. But those effects disappear when breastfeeding stops – hardly the kind of lifelong benefits touted by breastfeeding enthusiasts. “If you go into any kindergarten class and ask the teacher to guess which of these children were breastfed and which were formula fed, they couldn’t tell you,” says Barston.

It could be argued that as we know breastfeeding has some benefits, there’s no harm in exaggerating them to boost its popularity. But that’s treating women like children – medicine isn’t supposed to be this paternalistic any more.

And it can’t be right to give out misinformation when people need to make such a complex and personal judgement call at what can be a very stressful point in their lives. Only the women themselves can weigh up the benefits of breastfeeding with how it affects their mental and physical health, or perhaps the time they can spend with their other children or a financial need to go back to work.

In the US, women who take maternity leave are only off for an average of 10 weeks – nearly a third take none at all.

After all, it is very hard to breastfeed exclusively if you are working out of the home full-time. Countless leaflets and posters claim that breastfeeding is free but that only holds true for as long as the mum can afford to be on maternity leave. In the US, women who take maternity leave are only off for an average of 10 weeks – nearly a third take none at all.

The current veneration of breastfeeding has some upsides. There is more specialist help available in hospitals for women who are having trouble getting their baby to latch on properly. There’s also more awareness that women should have the right to nurse in public without facing tuts and disapproving looks.

Certainly, no one is suggesting that we withdraw that support. Campaigners like Barston simply want women to be free to make up their own minds, based on the known facts and their own circumstances, without judgement. “There has to be a way to give support for breastfeeding without demonising formula,” Barston says. “We haven’t figured it out yet.”

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Clare Wilson is a medical journalist at New Scientist. She tweets at @clarewilsonmed

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