Breastfeeding can cut the chances of a child becoming obese by up to 25%, according to a major study involving 16 countries.

World Health Organisation (WHO) experts who led the Europe-wide research are calling for more help and encouragement to women to breastfeed, as well as curbs on the marketing of formula milk which, said senior author Dr João Breda, misled women into thinking breast was not necessarily better.

“We need to see more measures to encourage breastfeeding, like properly paid maternity leave,” said Breda from the WHO European Office for Prevention and Control of Noncommunicable Diseases.

“We need less inappropriate marketing of formula milk, which may lead some mothers to believe it is as good for babies as breast milk.”

The research found more than 77% of children across Europe were breastfed, but rates varied widely. In Ireland, 46% of mothers had never breastfed and in France, that was nearly 34%. WHO recommends that women should exclusively breastfeed for six months, if they can.

The data came from nearly 30,000 children monitored as part of the WHO Childhood Obesity Surveillance initiative (Cosi). Launched in 2007, Cosi is continuously being updated and now receives data from about 40 countries on children aged six to nine – though not the UK, which measures children in school at around aged four and 11.

UK breastfeeding rates are low. Although 81% of mothers in the UK begin to breastfeed, by six weeks that has fallen to 24% in England, 17% in Wales and 13% in Northern Ireland according to the latest data, from 2010. By six months, only 1% are exclusively breastfeeding, although 34% are still doing some breastfeeding.

In absolute terms, 16.8% of children who were never breastfed were obese, compared with 13.2% who had been breastfed at some time and 9.3% of children breastfed for six months or more.

After adjustment for demographics, children who were never breastfed were 22% more likely to be obese and those who had been breastfed for less than six months were 12% more likely to be obese than children who were breastfed for six months. The protection for children who were exclusively breastfed for six months – with no formula or weaning foods involved – was even higher, at 25%.

WHO’s paper, presented at the European Congress on Obesity in Glasgow and published in the journal Obesity Facts, says there are a number of reasons breastfeeding would protect children from obesity. Exclusive breastfeeding delays the introduction of solid food, which may be high in energy. There is also some evidence that babies fed formula have higher insulin levels in their blood which can stimulate fat deposition.

But other factors could include healthier lifestyles among families where women breastfeed, acknowledged Breda. Whatever the reasons, women should be told that breastfeeding protects against obesity, he said. “Breastfeeding has a really strong protective effect. The evidence is there. The benefit is outstanding so we should be telling people.”

Kate Brintworth, head of maternity transformation at the Royal College of Midwives, said the study reinforced the need to put more resources into supporting women to breastfeed.

“We need both more specialist breastfeeding support for women after the birth and more time for midwives to offer the support women are telling us they need,” she said.

“We know that in the postnatal period many women are saying they don’t feel midwives and midwifery support workers have the time to give them the support that would enable many more to continue breastfeeding.

“However, it is important that we respect a woman’s infant feeding choices, and that if a woman chooses not to breastfeed, for whatever reason, she will need to be supported in that choice.”

Sue Ashmore, director of the Unicef UK’s Baby Friendly initiative which accredits maternity hospitals and other services that support women to breastfeed to a high standard, said: “Human milk – breast milk – is specifically designed for human babies. Not only does it act as baby’s first vaccine, protecting against infections, but it also affects long-term health, including acting as the first defence against the epidemic of obesity.

“In the UK we have some of the lowest breastfeeding rates in the world … In addition, infant feeding is a highly emotive subject because so many families have not breastfed or have experienced the trauma of trying very hard to breastfeed and not been able to. We need more support to help new mothers learn breastfeeding skills, and policies in place that will help them to continue breastfeeding through the first year of life.”