Researchers warn of an important new driver of cancer in under-50s – and it’s not smoking or poor diet

A new study has found that 11 types of cancer are on the rise in the 20 to 49-year-old age group, with obesity emerging as a significant driver behind the escalating rates among individuals under the age of 50.

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.

While researchers caution that obesity does not fully explain the trend and further evidence is required, scientists believe that being overweight or obese plays a crucial role, potentially due to elevated levels of insulin and inflammation.

Concerns have been mounting in recent years over the increasing incidence of cancers, such as bowel and ovarian, in young adults.

In England, approximately 31,000 cancers were diagnosed in people aged 20 to 49 in 2023, equating to roughly one in every 1,000 individuals.

This contrasts with 244,000 cases diagnosed in the 50 to 79 age group, where the rate was about one in 100.

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.

Experts at the Institute of Cancer Research, London (ICR) and Imperial College London conducted the new study.

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.

Professor Montse García‑Closas from the ICR said more research is needed, but “we cannot wait to act”.

García‑Closas said data suggested around 15 per cent of bowel cancer in younger people could be down to being overweight or obese, with around 40 per cent to 50 per cent 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.”

Among the younger cohort, breast cancer was the most common with 8,500 cases, followed by bowel cancer at 3,000 and melanoma skin cancer with 2,800 diagnoses.

They found that despite the rise in several cancer rates among younger adults over the past two decades, most established risk factors – including smoking, alcohol consumption, red or processed meat intake, low fibre diets, and lack of exercise – remained stable or even declined in the period leading up to diagnosis.

This suggests that these traditional factors are unlikely to substantially account for the observed increase in cancer cases.

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.

The team suggested that between 2001 and 2019, around 20 per cent 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.

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.”