A groundbreaking study from the University of Oxford has challenged one of the most deeply held beliefs about children’s health—that obesity alone drives medical costs and attention. New evidence reveals that underweight children can be just as medically vulnerable and costly to the healthcare system as those who are obese, forcing experts to rethink how weight problems are defined and treated.

Published in JAMA Network Open and funded by the National Institute for Health and Care Research (NIHR), the study used NHS electronic health records from more than 268,000 children aged 2 to 15 across England. It found that weight-related health problems—both at the lower and higher ends of the scale—cost the NHS an estimated £340 million each year.

Dr Olu Onyimadu, lead author from Oxford’s Nuffield Department of Primary Care Health Sciences, explained, “It’s not just obesity that drives costs. Underweight children may need comparable support and generate similar healthcare costs per capita to the NHS. We need to think about the full spectrum of unhealthy weight when planning services.”

The data showed that healthcare costs rose sharply after a child’s weight was formally recorded during GP visits—indicating that diagnosis itself acts as a trigger for medical support. For children with severe obesity, excess healthcare costs averaged £472 a year. Yet underweight children showed a similar pattern of higher GP appointments, nutritional consultations, and diagnostic testing once their condition was officially noted.

The study also revealed gender and ethnic differences. Girls with severe obesity cost more in healthcare than boys (£253 vs £138 annually), while only White children showed consistently higher costs across all unhealthy weight groups.

Experts say the findings come at a crucial time, as the government’s 10-year health plan emphasises switching from treatment to prevention. “These numbers give commissioners and practices the evidence they need to make the case for weight-management services,” said Professor Stavros Petrou, NIHR Senior Investigator and co-author.

However, this growing awareness also raises questions about the side effects of common drugs prescribed for weight-related conditions in children. Appetite stimulants, metabolic enhancers, or psychiatric medicines used to manage anxiety-related eating issues can unintentionally affect metabolism, heart rate, or hormonal balance. According to the UK’s National Institute for Health and Care Excellence (NICE), over-reliance on such medications without behavioural or nutritional intervention can create a cycle of dependency and secondary complications.

Doctors caution that medication should only be considered as a final option. “The goal should be to identify underlying causes—nutritional gaps, stress, sleep disorders—before turning to drugs that may carry unintended effects,” said Dr Onyimadu.

For parents, the message is simple but vital: getting a child’s weight checked regularly is key. Whether a child is too thin or too heavy, identifying the problem early unlocks access to proper support—from diet counselling and psychological care to community-based nutrition programmes.

The study’s authors believe these findings could reshape public health strategy and lead to more equitable allocation of healthcare resources. Professor Mara Violato from Oxford Population Health noted, “With 27% of children aged 2–15 living with overweight or obesity, plus those affected by underweight, we have a major opportunity for preventive care.”

Ultimately, the research reframes childhood weight as a spectrum of risk, not a single condition. And by recognising both underweight and obesity as serious medical concerns, it encourages a more balanced approach—one that prevents unnecessary drug dependence and focuses on long-term, holistic child health.