Obesity Identified as Key Driver of Rising Cancer Rates in Younger Adults

Key Takeaways: 

• A major new study has found that overweight and obesity are likely to be significant contributors to rising cancer rates among younger adults in England.
  
• Researchers found that many traditional behavioural cancer risk factors – including smoking, alcohol consumption and physical inactivity – have remained stable or improved over the past two decades, making them unlikely to fully explain the increase in early-onset cancers.
  
• Although excess weight appears to play an important role, researchers say it cannot entirely account for the rise in cancers such as bowel cancer, suggesting that additional biological, environmental and early-life factors may also be involved.
  
  
  

Study highlights growing concern over early-onset cancer

Being overweight or living with obesity may be a key driver behind rising cancer rates in younger adults in England, according to a major new study led by researchers at The Institute of Cancer Research, London, and Imperial College London.

The analysis, published in BMJ Oncology, examined trends in cancer incidence alongside changes in known behavioural cancer risk factors over nearly two decades. Researchers found that while rates of several cancers among younger adults have continued to increase, many established lifestyle-related risk factors have either improved or remained stable during the same period.

These findings led researchers to conclude that obesity is likely to be one of the most important contributors to the increase in cancer incidence among younger generations in England.

At the same time, the researchers stressed that rising body mass index (BMI) alone does not fully explain the growing number of cancer cases, indicating that additional factors may also be contributing to the trend.

Researchers analysed cancer trends across England

The research team used national cancer registry data from England covering the years 2001 to 2019. The study was conducted by scientists from the Cancer Epidemiology and Prevention Research Unit (CEPRU) at both The Institute of Cancer Research (ICR) and Imperial College London.

Researchers examined incidence trends across:

• 22 cancer types in women
• 21 cancer types in men

From this analysis, they identified 11 cancers that are increasing among adults aged between 20 and 49 years and are associated with known behavioural risk factors.

All of the cancers identified – except oral cancer – are recognised as being linked to excess weight.

For most cancer types, increases seen in younger adults mirrored trends observed in adults aged over 50, where the overall disease burden remains considerably higher. However, bowel cancer and ovarian cancer stood out as notable exceptions because rates were increasing only among younger age groups.

Most traditional risk factors have improved

The study examined trends in several well-established behavioural cancer risk factors, including:

• Smoking
• Alcohol use
• Overweight and obesity
• Physical inactivity
• Red and processed meat consumption
• Low fibre intake

Together, these risk factors accounted for an estimated 40–50 per cent of bowel, endometrial, oral and liver cancer cases in 2019.

However, researchers found that trends for most of these risk factors have either remained stable or improved over time, making them unlikely to substantially explain the recent rise in cancer incidence among younger adults.

According to the analysis:

• Smoking among younger adults has fallen by approximately two per cent annually over the past two decades.
• Alcohol consumption has largely stabilised or declined.
• Physical inactivity has decreased.
• Consumption of red and processed meat has reduced.
• Fibre intake, while still below recommended levels, has gradually improved.

In contrast, rates of overweight and obesity have steadily increased since 1995.

The largest increases in obesity were observed among younger women, where obesity prevalence rose by approximately 2.6 per cent relative increase per year.

Obesity linked to rising bowel cancer rates

The researchers found evidence linking rising BMI to increasing bowel cancer rates among younger adults.

Among younger women, bowel cancer rates associated with BMI rose from 0.9 to 1.6 cases per 100,000 people. In comparison, bowel cancer rates not attributable to BMI increased from 6.4 to 9.6 cases per 100,000 people.

Similar patterns were also observed in men.

However, the authors emphasised that the total number of BMI-linked bowel cancer cases remained lower than the number of cases not linked to BMI. This suggests that although obesity is an important contributor, it cannot fully explain the scale of the increase in bowel cancer among younger adults.

Additional causes may be contributing

The study points to the likelihood that multiple interacting factors are contributing to rising cancer rates in younger generations.

Several suspected contributors have previously been proposed, including:

• Ultra-processed foods
• Antibiotic use
• Air pollution

However, researchers noted that many of these exposures have also shown relatively stable or declining trends in the UK, complicating efforts to identify the main drivers of early-onset cancers.

The authors also highlighted emerging evidence suggesting that obesity-related mechanisms not fully captured by BMI may influence cancer risk. These include:

• Metabolic dysfunction
• Chronic inflammation
• Alterations in the gut microbiome

Further research is needed to determine whether these mechanisms directly contribute to the development of bowel cancer and other cancers in younger adults.

Experts say more research is urgently needed

The researchers called for large-scale, long-term studies capable of tracking exposures across the entire life course in order to better understand what is driving rising rates of early-onset cancers.

Professor Marc Gunter, Co-Director of the Cancer Epidemiology and Prevention Research Unit at Imperial College London, said:

“The changes we’re seeing in cancer incidence, particularly the rates of some cancers in younger adults, don’t have a single cause or a simple answer. They reflect a complex mix of generational effects, gaps in long-term exposure data, and shifts in diagnosis and detection, and show how much more scientists still need to understand about when and how cancer develops across the life course. While rising rates in younger adults are concerning, it remains crucial not to lose sight of cancer trends in older adults, where the absolute burden of disease is still far greater.”

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, said the findings indicate that behavioural changes alone cannot explain current trends.

She said:

“Our findings show that while cancer rates are rising in younger adults, the trends are unlikely to be explained by changes in most known behavioural risk factors. Smoking, alcohol and other behaviours have been stable or improving for two decades, yet early-onset cancers continue to increase – particularly bowel cancer.

“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.

“However, 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.”

Calls for stronger prevention and public health action

The findings have prompted renewed calls for stronger public health measures aimed at preventing obesity and improving cancer prevention strategies across all age groups.

Professor Kristian Helin, CEO of The Institute of Cancer Research, London, said the study highlights an urgent public health challenge requiring coordinated action across research, prevention and policy.

He said:

“This work highlights a growing public health challenge and the need for urgent action across research, prevention and policy. Although rising cancer rates in younger adults are concerning, the burden remains overwhelmingly higher in older people, which means prevention efforts must span all ages.

“This study makes clear that traditional lifestyle risks alone cannot explain current trends – pointing to the importance of investigating other exposures such as the potential role of the microbiome, while strengthening strategies to address obesity and other established risks. To protect future generations, we must invest in understanding the causes of cancer at all ages and ensure that early diagnosis, screening and prevention strategies keep pace with a changing population.”

CCH insights:

The outcomes of this study are concerning but not entirely surprising, given that obesity rates in children and young people are still rising and obesity is a significant risk factor for many cancers. It adds further support for the call to treat obesity at the earliest opportunity, regardless of the age of the individual. The longer obesity goes untreated the greater the risk of individuals developing serious chronic diseases such as cancer, type 2 diabetes and heart disease.