7 Myths And Facts About Breastfeeding

The World Health Organisation has released a major series of studies into the effects of breastfeeding. Here's a breakdown of the evidence.

The World Health Organisation (WHO) has hailed the benefits of breastfeeding on the back of some new studies.

The studies are published in the medical journal The Lancet. It says that boosting breastfeeding levels to "near-universal levels" could save 800,000 lives a year, and that breastfeeding prevents various diseases and improves children's intelligence.

Last year, BuzzFeed looked at the evidence behind some of the claims made for breastfeeding. We have now updated it in response to the WHO/Lancet data.

1. There's not much good evidence that breastfeeding makes your child smarter.

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There was a widely reported study in April 2015 that suggested that breastfed babies are more intelligent, and the longer they're breastfed, the more intelligent they tend to be.

But Dr Stuart Ritchie of the Centre for Cognitive Ageing at the University of Edinburgh points out that parents who are more intelligent tend to breastfeed, and parents who are more intelligent also tend to have more intelligent children. When studies control for parental intelligence, he says, "the biggest and best studies find no relationship". He points to a major review of the literature, published in the BMJ in 2013, which looked at 80 studies and found that "the initial positive effect of breastfeeding on IQ disappeared or diminished" in studies that looked at parental IQ.

Still, the breastfeeding-intelligence link gets brought up fairly often, says Ritchie. "It's a weird amnesia in the media – there's loads of research and every time people forget."

We asked Ritchie about the new Lancet/WHO data, and he says it suffers from the same problem.

It's based on a meta-analysis published in the journal Acta Paediatrica, and it found that breastfeeding was linked to a 3.44-point increase in IQ. However, when it looked at studies that controlled for maternal IQ, that increase got smaller – down to 2.62 points. And, most interestingly, the smaller, weaker studies that the analysis looked at were much more likely to find an improvement than larger, better studies. That's often an indicator that the result is a fluke, rather than a real effect. Ritchie notes that the authors of the study didn't do any of the standard statistical tests to rule that out.

"I'd disagree with the authors of the meta-analysis," he says. "If you combine the facts that, a), studies with proper controls for maternal IQ get smaller effects, and b), studies with bigger samples get smaller effects, the breastfeeding IQ effect looks pretty unconvincing."

2. Breastfeeding does protect your baby against infections while it's young.

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Linda Geddes, the author of the science-of-parenthood book Bumpology, told BuzzFeed: "There have been lots of studies on breastfeeding, and they show real short-term benefits. They give babies antibodies which protect against diarrhoea and chest infections and things like that. All that's pretty well-established."

This is especially important in the developing world, where infections are a real killer: The Lancet/WHO data finds that children in lower or middle-income countries are several times more likely to die in their first two years if they are not breastfed, probably because of the risk of infections from bottled formula. The WHO says that if breastfeeding were "near universal" in 75 low- and middle-income countries, it would save 823,000 children's lives a year.

However, the results are much less clear for the developed West.

The Lancet/WHO study says that breastfeeding "might also protect against deaths in high-income countries", looking at a report published by the US Agency for Health Care Policy and Research. The report itself, however, warns that "one should not infer causality based on these findings".

In Bumpology, Geddes points out that there is good evidence that breastfeeding protects against sudden infant death syndrome, or SIDS, which used to be known as cot death. But, she says, the protective effect is small: "5,500 children would have to be breastfed to prevent one death."

3. Breastfeeding probably does make your child slightly less likely to be obese.

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There is conflicting evidence here, and it's very complicated teasing out cause and effect. But, in 2013, a major meta-analysis by the World Health Organisation examined 71 studies into whether breastfeeding protects children against obesity in later life. After controlling for other factors, they found a "relatively modest" protective effect: "a small reduction, of about 10%, in the prevalence of overweight or obesity in children exposed to longer durations of breastfeeding". The new Lancet/WHO data found a similar effect – 13% – after adjusting for the fact that better-off people are both less likely to be obese and more likely to breastfeed.

It may also have a small protective effect against blood pressure and blood cholesterol, according to another WHO analysis.

4. It's not clear whether breastfeeding protects against diabetes.

"Where it gets more complicated is whether it protects against allergies, diabetes, and things like that," says Geddes. "Some studies say it does, some say it probably doesn't, and the biggest and best studies tend to find no protection."

You'll find people saying that breastfed children are less likely to suffer from diabetes. It's true, but as with the intelligence thing, it's hard to determine whether breastfeeding causes this. Two meta-analyses, one in 2007 and one in 2014, found that there's not enough evidence to draw firm conclusions: "The role of body weight as a mediator or confounder remains uncertain," one says, and "At this stage, it is not possible to draw firm conclusions… Further studies are badly needed on this topic" says the other.

The new WHO/Lancet data, again, is unclear. Although it looked at 11 studies, which, all together, showed some effect, it said that only three of those studies were high quality, and the evidence from those three was not strong enough to reliably show an effect.

5. Breastfeeding protects mothers against breast cancer, a bit.

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A 2000 meta-analysis found that breastfeeding reduces the risk of breast cancer in later life. However, the protective factor is "of small magnitude compared with other known risk factors". A later review, in 2003, found something similar: a small (about 4%) reduction in relative risk. In Bumpology, Geddes quotes studies suggesting a larger effect: "breastfeeding for more than 12 months is associated with a 28% decrease in [breast and ovarian] cancer risk".

The WHO quotes a meta-analysis that says that breastfeeding for six months is associated with a 7% drop in breast cancer risk compared to women who never breastfed at all, while breastfeeding for a year is associated with a 9% drop. It says that around 20,000 breast cancer deaths could be prevented worldwide if breastfeeding was "near universal".

However, it should be borne in mind that 135 million women give birth worldwide per year, and less than half of them exclusively breastfeed for six months. The 20,000 figure should be seen in that context.

6. People tend to overstate some of the benefits of breastfeeding.

There have been some dramatic claims made about the protective effect of breastfeeding. The US National Breastfeeding Awareness Campaign (NBAC) used to say that breastfed babies have a reduced risk of ear infections, respiratory illnesses, diarrhoea, and obesity, diabetes, and leukaemia. The US Ad Council claimed that children who weren't breastfed for six months had a higher risk of "asthma, allergies, diabetes and cancer; suffer more colds, flu and other respiratory illnesses".

The trouble is, as we've seen above, it's really hard to tease out the effects of breastfeeding. People who breastfeed tend to be healthier, wealthier, better-educated, and so on than people who don't.

It's also particularly hard for working women to breastfeed, especially those on shift work, and some women find it painful or impossible. As this analysis in the Journal of Health Politics, Policy and Law points out, overstating the relative benefits of breastfeeding risks provoking unnecessary anxiety among non-breastfeeding women.

7. The most important thing is that the mother is healthy and happy.

There are real advantages to breastfeeding, but some of the claims about it are overdramatised and uncertain. And the risks of placing undue pressure on mothers are real, if it pushes them into postnatal depression. "What there is good evidence for is that maternal depression is bad for children," says Geddes. "Depressed mothers find it harder to form a secure attachment with their babies, and the babies have a harder time forming relationships in later life. I don't think guilt is good for mums.

"There are lots of other things you can do boost your child's chances. If you're not inclined to breastfeed, you're not a bad mother."