Social attitudes that deter women from breastfeeding for more than a few weeks in the UK need to change in the interests of babies’ health, experts say.

The UK has one of the lowest rates of breastfeeding in the world, even though the medical evidence shows it protects babies from infection and improves their mental and physical development.

Prof Neena Modi, president of the Royal College of Paediatrics and Child Health, one of the signatories to a letter sent to the Guardian calling for a change in attitudes, said she was disturbed that their research had found children thought breastfeeding was “yukky” and added that “society is ambivalent about women’s bodies”.

Some women who have just given birth say their partners would not be happy if they breastfeed, she said. “Perhaps many men feel discomforted because they grow up to regard the breast as a sexual object,” she told the Guardian. “In which case I suggest that they should put these attitudes well and truly behind them.”

Women who choose to breastfeed in public occasionally find themselves in the headlines. Louise Burns, 35, protested in 2014 over a request by staff at Claridge’s hotel in London that she should cover herself and the baby while breastfeeding in the tearoom.

Some prominent women in other countries have deliberately chosen to break the mould, making headlines around the world. Senator Larissa Waters became the first politician to feed her baby during a vote in Australia’s parliament in May.

Aliya Shagieva, youngest daughter of the Kyrgyz president, posted a photograph on social media in April of herself feeding her baby in her underwear with the caption: “I will feed my child whenever and wherever he needs to be fed.” In the ensuing furore and acknowledging the disapproval of her parents, she took the post down.

Modi said there is an assumption that breastfeeding is not important in a developed nation like the UK. Yet it will benefit the children of the affluent just as much as the least well-off, from protecting them from obesity to potentially improving their performance in the classroom.

“If someone was selling rich middle class parents some wonderful new whatever to improve their children’s intellectual ability, it would probably sell like hot cakes. And breast milk is absolutely just that,” she said. “Society is riddled with contradictions and muddled thinking about breastfeeding.”

In the letter, the presidents of five royal colleges and heads of expert organisations call for the “multiple barriers” to breastfeeding in the UK to be overturned. “Though some women are unable to breastfeed and some choose not to, with the right support, the vast majority of women are able to breastfeed successfully,” it says.

Although nearly three-quarters of new mothers begin to breast feed, within two months less than half are still doing it, in spite of the many benefits to the growing baby. By six months, only a third (34%) of UK babies are receiving any breast milk, compared with 49% in the United States and 71% in Norway. Only 1% are exclusively breastfed to six months, as the World Health Organization recommends.

Some women feel they are being criticised by the pro-breastfeeding lobby. Modi says that healthcare professionals should be careful not to make them feel this is something that is hard to learn and do properly. “Haranguing women and being overly dogmatic is not the way forward,” she said. “We’d like women going into this anticipating that it will be a wonderful, joyous thing, rather than what seems to be happening in some cases, with women slightly worried and fearful that they are going to be failures.”

Schools should teach children that breastfeeding is natural and healthcare services should give practical support, say the signatories, who include Alison Thewlis MP, chair of the all-party parliamentary group on infant feeding and health inequalities, Sue Ashmore, of Unicef UK’s Baby Friendly Initiative and Justine Roberts, founder of Mumsnet.

“Above all, social attitudes towards breastfeeding must improve,” they write. “Women, their partners and families must feel comfortable about breastfeeding as a normal natural part of everyday life. In short, the solutions lie with all of us.”

Their letter comes as Unicef and the WHO publish a new report warning that thousands of babies are dying across the world and economies losing billions of dollars for want of breastfeeding.

No country in the world meets the standards promoted by the WHO, they say. Worldwide, only 40% of babies are breastfed exclusively for six months. Only 23 countries out of 194 have achieved six months’ exclusive breastfeeding for at least 60% of babies.

Breastfeeding “offers children unparalleled health and brain-building benefits. It has the power to save the lives of women and children throughout the world, and the power to help national economies grow through lower healthcare costs and smarter workforces. Yet many societies are failing to adequately support women to breastfeed,” says the report.

The report spells out the human and economic cost to countries that fail to support breastfeeding. In five of the world’s largest emerging economies – China, India, Indonesia, Mexico and Nigeria – the lack of investment in breastfeeding results in an estimated 236,000 child deaths per year and US$119bn (£90.3bn) in economic losses, it says.

Increasing the proportion of babies globally that are breastfed exclusively for six months to 50% by 2025 could save the lives of 520,000 children under the age of five and potentially generate US$300bn in economic gains over 10 years by reducing illness and healthcare costs and increasing productivity, says the report.

“Breastfeeding is one of the most effective – and cost effective – investments nations can make in the health of their youngest members and the future health of their economies and societies,” said Unicef’s executive director, Anthony Lake. “By failing to invest in breastfeeding, we are failing mothers and their babies – and paying a double price: in lost lives and in lost opportunity.”