Increasing obesity prevalence may play an important role in rising cancer incidence among younger adults, while trends in other established behavioural risk factors have remained stable or declined, according to a recent analysis.

The incidence of a growing number of cancers in younger adults has attracted attention in recent years, prompting questions about whether changing lifestyle and behavioural risk factors are driving these trends.

To address this issue, teams from The Institute of Cancer Research and Imperial College London analysed national cancer incidence and population health survey data from England to determine whether temporal changes in established behavioural risk factors aligned with rising cancer rates in younger adults.

With the results published in BMJ Oncology, the researchers examined national cancer registry data from England between 2001 and 2019, covering 22 cancer sites in women and 21 in men.

They identified cancers with significantly increasing incidence among adults aged 20–49 years and assessed trends in smoking, alcohol consumption, body mass index (BMI), physical inactivity and dietary factors using population-based health surveys.

Population attributable fractions were also calculated to estimate the proportion of cancers linked to these exposures.

A total of 11 cancers with recognised behavioural risk factors showed increasing incidence in younger adults. These included colorectal, pancreatic, kidney, liver, thyroid and oral cancers, as well as breast, endometrial and ovarian cancers in women.

For most cancer types, incidence also increased in adults aged 50 years and older, although colorectal and ovarian cancer were notable exceptions, with increases confined to younger adults.

Obesity as a major behavioural risk factor

Established behavioural risk factors accounted for a substantial proportion of cancer burden. Depending on tumour type, population attributable fractions ranged from approximately 7% to 65%.

However, obesity was the only major risk factor that consistently increased in prevalence during the study period.

In contrast, smoking prevalence declined, alcohol consumption generally fell or remained stable, physical inactivity decreased, and red and processed meat consumption dropped substantially.

When obesity-related cancers were examined in more detail, it was found that both BMI-attributable and BMI-non-attributable cancer incidence rates increased over time.

Although obesity-related incidence rose more rapidly, the increase in non-attributable cancers suggested that excess weight alone could not fully explain the observed trends.

Lead author 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, 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.

Priorities for further investigation

The authors suggested that additional influences, including early-life and prenatal exposures, changes in the gut microbiome, environmental factors and evolving diagnostic practices, may help explain rising cancer incidence among younger generations.

Colorectal cancer was deemed a priority for further investigation as its incidence continued to rise in younger adults while remaining relatively stable in older populations.

However, the study had several limitations. Long-term national exposure data were unavailable for some risk factors, physical activity definitions changed over time, and the analysis assumed a 10-year lag between exposure and cancer development, the authors said.

Changes in screening, diagnostic technologies and possible overdiagnosis may also have influenced incidence trends.

Professor García‑Closas added: ‘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.’

Reference
Garcia-Closas M et al. Temporal trends in behavioural risk factors for cancers with rising incidence in younger adults: an analysis of population-based data in England. BMJ Oncol 2026;5(1):e000966.