Almost one in four children aged 10 and 11 in England are obese, according to the largest study of its kind – a finding that experts say exposes the “profound” and “alarming” long-term impact of the coronavirus pandemic. Obesity rates increased by 45% in four-to-five-year-olds and by 21% in 10-to-11-year-olds during the first year of lockdowns, the analysis involving more than 1 million children reveals. The prevalence of obesity among younger, reception-age children has since largely returned to expected – though still concerning – levels, but the proportion of children leaving primary school overweight, obese or severely obese remains much higher than before the pandemic. Experts said this was probably because while younger children reverted to healthier lifestyles, in many older children, poor eating habits, insufficient exercise and harmful levels of screen time had become embedded. NHS England’s national clinical director for children and young people said the figures were alarming and represented a “ticking health timebomb”. The surge in children becoming overweight and obese during the pandemic means at least 56,000 more children will grow up at heightened risk of type 2 diabetes, cancer and other serious illnesses, researchers from the National Institute for Health and Care Research Southampton Biomedical Research Centre and the University of Southampton said. Their study, published in the journal PLOS One, also found that the sharp uptick would cost the UK more than £8bn in additional spending on healthcare and impact on the economy. Prof Mark Hanson, an emeritus professor of human development and health at Southampton and a co-author of the study, said the findings were horrifying. “Nearly one in four children leaving primary school are living with obesity, which is likely to have both an alarming effect on their health and wellbeing and a significant wider cost to society,” he said. Hanson said the figures warranted immediate action and that new policies should be aimed at the under-fives, given that in some cases obesity in older children “may be impossible” to escape. “Once established, obesity has proven to be difficult to reverse. Some 60%-85% of children with obesity remain obese in adulthood, increasing their risks of future ill-health.” Last month the Guardian revealed that children in England were facing an increased risk of serious health problems because ministers had shelved anti-obesity policies until 2025. The researchers behind the new study wrote in PLOS One: “During 2020-21, there were steep increases in overweight and obesity prevalence in children. By 2022, overweight and obesity prevalence in children aged four to five returned to expected levels based on pre-pandemic trends. However, overweight and obesity prevalence in children aged 10 to 11 persisted and was four percentage points higher than expected, representing almost 56,000 additional children. “The additional lifelong healthcare cost in this cohort [both children aged four to five and 10 to 11] will amount to £800m, with a cost to society of £8.7bn.” NHS figures released in October showed that the proportion of 10- and 11-year-olds who were overweight and obese had fallen slightly, but not back to pre-pandemic levels. Obesity levels in year 6 in England (10-11) were 25.5% in 2020-21, 23.4% in 2021-22 and 22.7% in 2022-23, compared with 21% in 2019-20. When obesity and overweight figures are taken together, 36.6% of children are an unhealthy weight, the most up-to-date figures show. Prof Simon Kenny, NHS England’s national clinical director for children and young people, said: “These figures will be as alarming to parents as they are to the NHS. Obesity affects every human organ system and so at a young age can have a major impact on a child’s life, increasing their risk of type 2 diabetes, cancer, mental health issues and many other illnesses, which can lead to shorter and unhappier lives.” The data showed that the prevalence of obesity in reception increased to 14.4% in 2020-21 and then fell to 10.1% in 2021-22 and 9.2% in 2022-23. This was lower than in 2018-19 and 2019-20 and suggests a trend of decline. Boys were more likely to be overweight than girls, the study found. Children living in the most deprived areas of England were twice as likely to be obese as those in the most affluent regions. Prof Keith Godfrey, of the Southampton Biomedical Research Centre, said: “The Covid obesity rates [have] reverted to approximately pre-pandemic levels in the reception-age children, but not in the older children, and we think that’s because the behaviours associated with increased rates of childhood obesity – reduced physical activity, poor diet and so on – become more embedded in the older children. Younger children reverted back to habitual diet, habitual levels of physical activity.” He said no one measure would solve childhood obesity but it must become a “national priority”. The NHS said it was committed to helping young people affected by weight issues through its new network of 30 specialist clinics, which offer tailored packages of physical, psychological and social support. Kenny added: “But the NHS cannot solve this issue alone, and continued joined-up action by industry, local and national government and wider society is needed if we are to avoid a ticking health timebomb for the future.” A government spokesperson said: “We are taking strong action to encourage healthier food choices and to tackle obesity across all socio-economic groups and in deprived areas, recognising that it is the second biggest cause of cancer and costs the NHS around £6.5bn a year.”