One key factor linked to surge in cancer among young adults

Scientists have identified one common factor that appears to be linked to a surge in cancer among younger people. Obesity is an important driver of rising cancer rates among the under-50s, a major new study suggests. While it does not explain the whole story and more evidence is needed, scientists said they believed being overweight or obese plays a role, possibly due to increased levels of insulin and inflammation. Researchers have become increasingly concerned in recent years about trends showing rising cancer rates in young adults, such as bowel and ovarian cancer. In 2023, around 31,000 cancers were diagnosed in people aged 20 to 49 in England – roughly one in 1,000 people. In contrast, far more (244,000) cases were diagnosed in those aged 50 to 79 – roughly one in every 100. Of the younger group, breast cancer was most common (8,500 cases), while bowel cancer accounted for 3,000 cases and melanoma skin cancer 2,800. In the new study, experts at the Institute of Cancer Research, London (ICR) and Imperial College London, found that while rates of several cancers have increased in younger adults over the past two decades, most known risk factors for these cancers – such as smoking, drinking alcohol, red or processed meats, low fibre intake and lack of exercise – were stable or declining in the run up to diagnosis. This means these factors are unlikely to substantially explain the increase in cancer cases, they suggested. In contrast, overweight and obesity, which have increased steadily since 1995, could be key factors in the rise of cases, the researchers found. However, the study, published in the journal BMJ Oncology, found that increases in body mass index (BMI) alone are not enough to explain the overall rise in cancer among younger adults in England. There must be other additional causes for the rise, whether suspected causes or currently unknown, the team said. Most cancers with rates rising in younger adults are also increasing in older adults, suggesting there are common causes between the two. Professor Montse Garcia-Closas, from the ICR, said data suggested around 15% of bowel cancer in younger people could be down to being overweight or obese, with around 40% to 50% in total down to the effect of combined known risk factors such as obesity, lack of exercise, alcohol and smoking. She told a media briefing: “Our main conclusion is that although BMI is our best clue, much of the increase still remains unexplained, and we’ve done some additional analysis that show that most likely what’s missing is not just a single cause unexplained, but it’s likely a combination of multiple factors that act together.” The team suggested that between 2001 and 2019, around 20% of the increase in bowel cancer was explained by the increases in BMI over this period of time. Professor Amy Berrington, from the ICR, said: “Although rates have been increasing, cancer in young people is still a rare disease.” Professor Marc Gunter, from Imperial, said obesity is a known risk factor for around 19 different cancers. He added: “For some of these cancers, including colorectal (bowel) cancer, we think this could be partly caused by higher levels of hormones such as insulin which is often elevated in people with obesity, as well as inflammation. “We know people with obesity have higher levels of insulin, and insulin is a growth factor and has been linked to cancer. In a recent study, we actually found that insulin in particular might be playing a role in early onset colorectal (bowel) cancer, and this is actually an area of very active research at the moment.” The researchers called for large, long‑term research studies to identify all biological and environmental factors that could explain rising cancer rates in young adults. However, they said the case is strong enough on obesity to make it a public health priority, particularly driving down obesity rates in children and young people. In the study, the team used national cancer registry data for England from 2001–2019. Some 11 cancers were identified as rising in the 20 to 49-year-old age group that have risk factors linked to people’s lifestyles and behaviour and can be altered to reduce risk. The 11 cancers were thyroid, multiple myeloma, liver, kidney, gallbladder, colorectal, pancreatic, endometrial, oral, breast and ovarian cancers. All of the 11 cancers identified, other than oral cancer, are known to be linked to excess weight, the researchers said. For nine of the 11 cancers, rates are increasing in younger adults but are also rising in older adults, who are much more likely to develop the disease. Bowel and ovarian cancer were the exceptions and were rising only in younger age groups. The researchers found that bowel cancer rates in younger women linked to BMI rose faster (from 0.9 to 1.6 per 100,000 people) than those not linked to BMI (from 6.4 to 9.6 per 100,000 people). Similar patterns were recorded for men. However, the authors noted that the overall number of cases of BMI-linked bowel cancer in younger women remained lower than those not linked to BMI – suggesting other factors must be contributing to the increase. Several suspected contributors – including ultra‑processed foods (UPFs), antibiotic use and air pollution – have been proposed in recent years. However, many of these factors have also shown stable or declining trends in the UK, reinforcing the need to thoroughly look at all reasons, the team said. Prof García‑Closas said more research is needed, but “we cannot wait to act”. She added: “Tackling obesity across all ages, particularly in children and young people, through stronger public health policies and wider access to effective interventions, could slow the rise in cancer and prevent many cancers – and must become a national priority.” Michelle Mitchell, Cancer Research UK’s chief executive, said: “Globally, and in the UK, we’re seeing a small increase in cancer rates in adults under 50. The picture is complex and we need more research to understand what’s driving the trend, but this study helps to fill in some gaps. “Overweight and obesity doesn’t explain the rise in full though. Improvements in detection are likely to also be playing a part, meaning that more people are being diagnosed at a younger age. Preventing cancer cases must be a priority for the UK Government. Smoking remains a leading cause of cancer in adults under 50, which is why the Tobacco and Vapes Bill receiving royal assent this week is such a historic moment. “Measures to restrict the advertising and promotion of junk food, introducing mandatory reporting and targets on healthy food sales, and making nutritious food more accessible to everyone would all help people keep a healthy weight.”