Explained: Why bowel cancer cases are on the rise in people under 50 years

Almost 2 million people are diagnosed with bowel cancer each year. Also known as colorectal cancer, it’s the third most common cancer worldwide.

While the majority of people diagnosed with bowel cancer are over 50, recent years has seen an alarming increase in the number of young people being diagnosed with the condition.

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In 2019, one study showed that in seven high income countries with historically high levels of bowel cancer, rates in the over-50s had begun to stabilise or even decline. This was attributed to the success of routine screening programmes that pick up pre-cancerous lesions before they have chance to develop into cancer.

But this same study also found that the disease was becoming more common in those under-50 in all countries analysed. For example, in Norway, the risk of developing rectal cancer (a type of bowel cancer) at an early age was five times greater for someone born in 1990 compared to someone born in 1920.

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More recently, a larger study which looked at bowel cancer rates in 50 different countries has revealed similar trends are happening across the world. Increasing rates of bowel cancer diagnoses were observed in countries in Europe, Latin America, the Caribbean and Asia – with many seeing the greatest increases in the under-50s.

While researchers aren’t entirely sure what’s fuelling this rise in young people specifically, it may be due to our increasingly unhealthy lifestyles.

What causes bowel cancer?

It’s been known for decades that the risk of developing bowel cancer is strongly influenced by a person’s lifestyle and environment.

For instance, a landmark study from 1968 showed that rates of bowel cancer were substantially higher in ethnically Japanese US citizens compared to the population in Japan – which, at that time, had comparatively low levels of the disease. This phenomenon, which has been backed up by many subsequent studies, strongly implicates a westernised lifestyle in promoting bowel cancer.

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In the years since, we’ve got a better idea of the factors that underpin this effect. Low physical activity levels, a diet low in fibre and high in fat or one that contains high amounts of red or processed meats, being overweight or obese, drinking alcohol and smoking are all linked with substantially higher risk of developing bowel cancer.

The impact these lifestyle factors have on the overall numbers of bowel cancer cases are significant. Cancer Research UK estimates that over half of UK bowel cancer cases are due to preventable causes.

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Meanwhile Japan, where rapid economic development has driven the adoption of an increasingly westernised diet, now has one of the highest rates of bowel cancer in the world.

Our increasingly sedentary lifestyles and the rising consumption of highly calorific, nutritionally poor foods probably plays a critical role in the generational changes in bowel cancer incidence we’re seeing. Such diets became increasingly commonplace through the US and parts of Europe in the 1970s – before spreading to other countries as a side-effect of economic development.

A worldwide obesity crisis

We’re also in the midst of a worldwide obesity crisis. It’s estimated that 2.2 billion people worldwide are overweight and 890 million of these are obese.

Worryingly, although rates of obesity are increasing among people of all ages, children and adolescents are disproportionately affected. Obesity is now ten times more common in children aged between five- and 14-years-old than in the mid-1970s.

This is significant, as many of the metabolic changes associated with obesity –such as dysregulated hormones and a chronic state of inflammation – are thought to help drive cancer development. Obesity is also associated with type 2 diabetes, which has been linked to increased risk of developing bowel cancer. Type 2 diabetes is also becoming increasingly common in younger people.

Our diet also has a big impact on the health of our gut microbiome – the population of trillions of bacteria and microbes that live inside us. Evidence suggests that a Western-style diet can promote a state of dysbiosis. This means the balance of the gut’s bacteria becomes disrupted – making it easier for harmful microbes to grow and reducing the growth of helpful bacteria.

It’s becoming increasingly clear that the composition of our microbiome can have a big impact on how likely we are to develop bowel cancer. One study even showed that the effects of gut dysbiosis on bowel cancer incidence may play an even greater role in younger patients than older ones.

Unfortunately, bowel cancer in the under-50s is often diagnosed at a late stage. This is in part due to screening programmes being targeted to over-50s. However, a survey by Bowel Cancer UK also highlighted a lack of awareness of the disease in younger people and their doctors as a contributory factor.

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Signs of bowel cancer

Early diagnosis is key to a better prognosis, so it’s important to be aware of the symptoms. Abdominal pain, bloody stools, changed bowel habits or unexplained weight loss can all be a sign of bowel cancer. Many of these can occur in the absence of cancer – but it’s important to get them checked out so cancer can be ruled out.

To reduce your risk of developing bowel cancer at any age, the message is very clear. Eat a healthy diet, limit your intake of ultra-processed foods and alcohol, don’t smoke and regularly exercise.

Sarah Allinson, Professor, Department of Biomedical and Life Sciences, Lancaster University

This article is republished from The Conversation under a Creative Commons license. Read the original article.