Healthcare (Commonwealth Union) – Scientists from the Institute of Cancer Research, London together with the Imperial College London reported that although several cancers have become more common among younger adults over the past 20 years, traditional behavioral risk factors—such as smoking, alcohol consumption, eating red or processed meat, low fibre diets, and lack of physical activity—have either remained steady or declined in England prior to these diagnoses. This suggests these factors are unlikely to be the main drivers behind the rising number of cancer cases.
Instead, the scientists found overweight and obesity to be key contributors, with a steady rise since 1995. The fastest increase was in younger women, whose obesity rates grew on average 2.6% annually during that time.
However, the study, published in BMJ Oncology, found that the rise in body mass index (BMI) alone can’t explain the overall increase in cancer cases, implying that other potential or as yet unknown factors could also be involved.
Marc Gunter, Co-Director of the Cancer Epidemiology and Prevention Research Unit at Imperial College London indicated that they are unable to explain the rise in cancer incidence, especially in younger people, by one factor. More likely, it is a complex interplay of generational influences, limited data on long-term exposure and changing approaches to diagnosis and detection.
He also stressed that while trends in younger adults are concerning, cancer continues to place a far greater overall burden on older populations.
Drawing on national cancer registry data in England from 2001 to 2019, researchers from the Cancer Epidemiology and Prevention Research Unit (CEPRU) at The Institute of Cancer Research and Imperial College London analysed incidence patterns across 22 cancer types in women and 21 in men. They found that 11 cancers are on the rise among adults aged 20–49, all of which are associated with recognised behavioural risk factors.
With the exception of oral cancer, all 11 identified cancers are linked to excess body weight. For most, the upward trend seen in younger adults reflects patterns observed in those over 50, where overall case numbers remain significantly higher. However, bowel and ovarian cancers stood out, as increases were observed only in younger age groups.
In 2019, well-established behavioural risk factors, such as smoking, alcohol consumption, overweight and obesity, lack of physical activity, diets high in red and processed meat, and low fibre intake, were estimated to be responsible for about 40–50% of cases of bowel, endometrial, oral and liver cancer. But the study found that trends for most of these other factors, except for overweight and obesity, have either levelled off or improved, so they are unlikely to be wholly responsible for the recent increase in cancer incidence.
Over the past 20 years, smoking rates among younger adults have declined by about 2% annually, alcohol use has largely levelled off or decreased, and physical inactivity has fallen. Consumption of red and processed meat has also dropped, while fibre intake, although still below recommended levels, has gradually increased.
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Professor Montserrat García-Closas, Co-Director of the Cancer Epidemiology and Prevention Research Unit and Group Leader in Integrative Cancer Epidemiology at The Institute of Cancer Research, London, stated that their results indicate that although cancer incidence is increasing among younger adults, this pattern is unlikely to be driven by shifts in most established behavioural risk factors. She further pointed out that over the past two decades, smoking, alcohol consumption, and similar habits have remained steady or improved, yet early-onset cancers — especially bowel cancer — continue to rise.
“Excess weight is an important contributor, although it cannot fully account for the scale of the rise in bowel and other cancers. This tells us that multiple factors — including early‑life exposures — may be acting together. Understanding these patterns is essential for identifying what is truly driving cancer risk in today’s generations. We now need deeper research, better measurement and continued surveillance to uncover the causes behind these worrying trends.
