Scientists have identified obesity as a significant factor linked to a surge in cancer cases among younger people, according to a major new study. While not the sole cause, being overweight or obese appears to play a role, possibly due to elevated insulin levels and inflammation.
Rising Cancer Rates in Young Adults
Researchers have become increasingly concerned about trends showing rising cancer rates in young adults, including bowel and ovarian cancer. In 2023, approximately 31,000 cancers were diagnosed in people aged 20 to 49 in England—roughly one in 1,000 individuals. In contrast, 244,000 cases were diagnosed in those aged 50 to 79, or about one in 100.
Among the younger group, breast cancer was most common (8,500 cases), followed by bowel cancer (3,000 cases) and melanoma skin cancer (2,800 cases).
Study Findings
Experts at the Institute of Cancer Research, London (ICR) and Imperial College London found that while rates of several cancers increased in younger adults over the past two decades, most known risk factors—such as smoking, alcohol consumption, red or processed meats, low fibre intake, and lack of exercise—were stable or declining before diagnosis. This suggests these factors are unlikely to substantially explain the increase.
In contrast, overweight and obesity, which have risen steadily since 1995, could be key drivers. However, the study, published in BMJ Oncology, found that increases in body mass index (BMI) alone do not fully account for the overall rise. Other additional causes, whether suspected or unknown, must be involved.
Common Causes Across Ages
Most cancers with rising rates in younger adults are also increasing in older adults, indicating shared causes. Professor Montse Garcia-Closas from the ICR noted that around 15% of bowel cancer in younger people could be attributed to being overweight or obese, with 40% to 50% linked to combined known risk factors like obesity, lack of exercise, alcohol, and smoking.
She stated: “Our main conclusion is that although BMI is our best clue, much of the increase still remains unexplained. It’s likely a combination of multiple factors that act together.”
Insulin and Inflammation
Professor Marc Gunter from Imperial College explained that obesity is a known risk factor for around 19 different cancers. For some, including colorectal cancer, higher insulin levels and inflammation may be contributing factors. “Insulin is a growth factor and has been linked to cancer. In a recent study, we found that insulin might play a role in early onset colorectal cancer,” he said.
The researchers called for large, long-term studies to identify all biological and environmental factors driving rising cancer rates in young adults. However, they emphasised that the evidence on obesity is strong enough to make it a public health priority, particularly reducing obesity rates in children and young people.
Specific Cancers on the Rise
The team analysed national cancer registry data for England from 2001 to 2019. They identified 11 cancers with rising rates in the 20–49 age group that have modifiable risk factors: thyroid, multiple myeloma, liver, kidney, gallbladder, colorectal, pancreatic, endometrial, oral, breast, and ovarian cancers. All except oral cancer are linked to excess weight.
For nine of these cancers, rates are increasing in both younger and older adults. Bowel and ovarian cancer were exceptions, rising only in younger age groups. Bowel cancer rates in younger women linked to BMI rose faster (from 0.9 to 1.6 per 100,000) than those not linked to BMI (from 6.4 to 9.6 per 100,000). Similar patterns were seen in men, though the overall number of BMI-linked bowel cancer cases remained lower, suggesting other factors are at play.
Other Potential Factors
Several suspected contributors, including ultra-processed foods, antibiotic use, and air pollution, have been proposed but often show stable or declining trends in the UK. The team stressed the need to thoroughly examine all reasons.
Professor Garcia-Closas said more research is needed, but “we cannot wait to act. 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, chief executive of Cancer Research UK, commented: “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.”
