Nearly 7,000 children and young Britons under 25 have been diagnosed with type 2 diabetes, the chronic condition linked to obesity that can lead to amputations and blindness.

Type 2 diabetes used to be virtually unknown in young people. It usually develops over the age of 40 in white Europeans, or after the age of 25 in people who are African-Caribbean, black African, or south Asian.

The startling new figures come from Diabetes UK, which has combined the numbers of children seen by hospital specialists with those for the young people up to age 25 who are looked after by their GP. Only 715 are receiving care from hospital units, but there are more than 6,000 in primary care, bringing the total to 6,836.

Prof Russell Viner, president of the Royal College of Paediatrics and Child Health (RCPCH), which made the hospital figures public earlier this year, said the new data confirmed the real total was higher than feared.

“When the RCPCH’s paediatric diabetes audit launched in the summer, we were concerned then that the numbers of children we were seeing with type 2 diabetes was an underestimate. This latest analysis, which takes primary care contacts into consideration, shows these concerns were justified and emphasises the need to act,” he said.

The first children diagnosed in the UK were girls aged between nine and 16 in the year 2000. But with a quarter of children overweight or obese when they start primary school, rising to a third by the time they leave at age 11, more and more are developing the chronic condition.

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Diabetes UK points out that the disease is more aggressive in young people than in adults, leading to a higher risk of complications developing earlier. These include blindness, amputations, heart disease and kidney failure.

“Type 2 diabetes can be devastating for children and young people,” said Bridget Turner, director of policy and campaigns, calling for greater commitment across society to measures for tackling obesity.

“We need to encourage healthy living by providing clear and easy-to-understand nutritional information about the products we are all buying, and protect children from adverts for foods that are high in fat, salt and sugar,” she said.

Viner called for the government to get on with introducing measures such as the curbs on TV adverts for junk food and supermarket promotions that it has proposed in its revised obesity plan, much of which is now in consultation.

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“For many children, the development of type 2 diabetes can be prevented with lifestyle changes but this isn’t easy – they need support. That’s why we were pleased to see the ambitious proposals set out in chapter 2 of its childhood obesity plan – we urge the government to maximise their impact by introducing them all and doing so quickly,” he said.

Caroline Cerny, lead for the Obesity Health Alliance, an umbrella group, said it was hugely concerning to see so many young people diagnosed with type 2 diabetes. “We know that obesity contributes to the development of this and other serious health conditions, and with one in three children leaving primary school with excess weight or obesity, these findings are worrying but sadly not surprising,” she said.

“What they highlight is the need for urgent action from government to help children and young people lead healthier lives. That’s why we want to see restrictions on junk food marketing before the 9pm watershed on TV, with similar restrictions applied online, action on the promotion of unhealthy products in shops, and industry going further to reduce sugar and calories from processed foods – all measures which can help families make healthy choices and prevent young people from developing potentially devastating diseases.”