CANCER RATES IN UNDER-50S ARE RISING – AND NO ONE CAN BE SURE WHY

One of the most concerning trends in cancer is that rates of the disease in people under 50 are on the rise. And we don’t know why.

Now, a group of respected British researchers say that part of the explanation is that people are getting fatter. But other experts are sceptical.

What do and don’t we know about this disturbing phenomenon – and what can people do to reduce their risk?

Cancer is a disease that usually affects older people, with nine in 10 tumours arising in people over 50.

That’s because cancer results from mutations in cells’ DNA, which causes them to start multiplying out of control. The older we get, the more time there has been for the mutations to happen.

The rise in cancer in the under-50s, known as early-onset cancer, has only come to much attention in the past few years, although analysis of long-term figures shows the trend has been happening for decades in many Western countries.

The rise is biggest in bowel cancer, with about a 50 per cent increase in under-50s since the 1990s in the UK. There are also smaller rises in this age group in tumours affecting over 20 other parts of the body.

It is especially puzzling because rates in the over-50s worldwide have been flat or even slightly declining for many tumour types, most studies suggest.

Lifestyle factors and cancer risk

The new study has investigated this by looking at lifestyle factors known to raise cancer risk to see if any of these could be responsible for the 22 tumour sites where early-onset cancers are rising. They used figures from registers of cancers in England between 2001 and 2019.

Eleven of these cancers have known behavioural risk factors. These are: obesity, smoking, drinking, lack of exercise, red and processed meat intake and lack of fibre in the diet.

Only one of these – obesity – has been increasing over the past few decades and could potentially explain the rise in cancer, the researchers said, whose study was published in the journal BMJ Oncology. Smoking, for instance, has been falling by 2 per cent a year over the past two decades, while alcohol intake has been either stable or declining.

That’s what led the researchers to claim that excess weight is “the strongest clue to the rise in cancers in under-50s. “The only risk factor that has been consistently getting worse over time is body mass index (BMI) or excess weight,” said Professor Montserrat García-Closas, a cancer expert at the Institute of Cancer Research in London, who led the research.

The fact that the steadily rising obesity rates in all Western countries are not good for our health is uncontentious. But this study did not prove that the rise in obesity is causing the rise in early-onset cancers – only that the two trends have been happening at the same time.

What’s more, when you take a closer look at the figures, the picture is more nuanced than it first appears.

When they looked at how much the rise in early-onset cancer could be blamed on rising obesity, they found it was only a small proportion.

It varied depending on the tumour type, but obesity never accounted for more than 25 per cent of the extra cases, and for some cancers it was as low as 1.5 per cent.

“Body mass index only explains a small part of the increase,” García-Closas acknowledged.

She said they had highlighted the potential role of obesity because it is common, and so if people managed to lose weight, it would reduce cancer rates in all age groups. “Although increases in BMI explain only a fraction of the rise in bowel cancer rates, we want to prevent all cancers, not only the excess [early-onset] cancers,” she said.

Needless to say, people can also reduce their risk of cancer by avoiding other known risk factors, such as smoking and heavy drinking.

Unlikely to be a single culprit behind rise

But, while it is true that being overweight raises our cancer risk, it is not as much as you might think. For bowel cancer, for instance, where the rise in early-onset cancers has been steepest, eight out of 10 cases are thought to have nothing to do with the person’s weight at all.

The latest study may not have been the best way to investigate the rise in early-onset cases because it looked at trends across populations rather than studying individuals, said Professor Paul Pharoah, a cancer epidemiologist at Cedars-Sinai Health Sciences University in Los Angeles, who was not involved in the work.

Professor Shuji Ogino, a pathologist at Harvard Medical School, said that the results might be misleading because the study did not look at risk behaviours far enough back in time. “Carcinogenic effects operate for decades,” he said. In other words, some of the established risk factors dismissed here might in fact be playing a role.

Other researchers are spreading their net wider than in this study, investigating if lifestyle factors not currently accepted as causes of cancer might be behind the rise in early onset cases.

Such potential new suspects include the advent of widespread antibiotic use in the 1960s, the growing consumption of processed foods, and compounds found in plastics known as “forever chemicals”, as they stay in the environment for a long time.

García-Closas said their figures suggested that multiple explanations may be responsible rather than one single culprit. If there is one single cause, it would have to be a previously unknown lifestyle risk factor with a large impact, increasing at a very steep rate – something that is unlikely to have been missed by the research community all this time, she said.

Finding out the cause of the rise has been deemed an urgent priority by Cancer Research UK and the US National Cancer Institute, two of the world’s biggest medical research funders. If we knew the answer, they would not have allocated millions of pounds to groups around the world investigating the question.

So, regardless of what some may claim about the rise in cancers, no one right now knows the real explanation.

2026-04-29T09:27:07Z