An image of the lining of our gut, which is home to a variety of species of bacteria.

This article is more than 3 years old. For a more recent picture, read our latest article on increasing cancer rates in adults under the age of 50.

Bowel cancer rates are increasing in adults aged between 20 and 50, according to data from 2 big studies published this week.

Both studies looked at large numbers of people across several countries, including the UK, providing strong evidence on the number of people developing bowel cancer. And some worrying trends emerged.

In the UK, bowel cancer cases increased on average by up to 7.3% each year in 30 to 39 year olds between 2005 and 2014, according to figures published by the International Cancer Benchmarking Partnership, which is part funded by Cancer Research UK.

But it’s important to put these percentage increases in perspective. As Professor Stephen Duffy, a cancer screening expert at Queen Mary University of London told the Science Media Centre, “Despite the recent increases, the incidence in people under age 50 remains very low in absolute terms.”

To put that into context, the increase amounted to 267 more cases of bowel cancer in 30-39 year olds in 2014 compared to 2005 in the UK.

But even though the numbers are relatively low, the same trend has not been seen in older adults. Which raises the question of just what is driving the increase in under 50s.

Don’t we already have a clear picture of what causes bowel cancer?

Bowel cancer is one of the most common cancers in the UK, so there’s lots of evidence looking at what can cause it to develop. Previous research has shown that regardless of age, overweight and obesity, a diet low in fibre and high in processed and red meat, drinking alcohol and not being active can all increase the risk of bowel cancer.

But while the new studies looked at trends in bowel cancer rates, neither study investigated what might be behind the changes.

“Both papers suggest that sedentary lifestyles, overweight and dietary factors may be partly responsible for this. This is almost certainly the case, but it is probably not the whole story,” says Duffy.

Risk factors like diet aren’t exclusive to under 50s, which suggests there may be something else going on. This could either be another factor contributing to the rise in this particular age group or something helping to stop any potential rise in older age groups.

There’s also some evidence that bowel cancer in younger people may be different to cancer in older people. These differences are visible at a DNA level and in where the cancer develops in the bowel. It’s these differences that scientists are hoping to take a closer look at.

Finding the missing pieces of the puzzle

We don’t yet know exactly what’s behind the increase in under 50s, but it’s likely that there’s more than just one explanation.

Researchers are working to shed light on unique causes that may explain the increase in bowel cancer in younger adults, exploring areas like genetics and our gut bacteria. It’s early days, but some research suggests that certain types of bacteria in our gut could be linked to bowel cancer.

We’re funding research to investigate bowel cancer in younger adults, including a study to understand the genetics of bowel cancer in people under the age of 40. We’re also funding an international team to investigate how the bacteria in our gut might influence both the development and treatment of bowel cancer, which we’ve blogged about before.

What does this mean for screening?

The UK already has a bowel cancer screening programme for older adults. And despite some headlines, these findings alone don’t point to a benefit in including adults under 50 in the screening programme.

Duffy says it’s too early to change the policy on bowel screening, as the number of cases in younger adults is still small. And to consider lowering the bowel screening age in the UK there would need to be evidence that the benefits would outweigh the harms in these younger age groups.

Bowel screening in the UK

The programme aims to detect bowel cancer before symptoms have developed.

It is available for adults between 60 and 74 in England, Wales and Northern Ireland, and adults aged between 50 and 74 in Scotland.

The English and Welsh Governments have committed to reducing the age to 50.

The bottom line

The rise of bowel cancer in younger adults is concerning and it’s vital we find out why it’s happening. But it’s important to remember that bowel cancer remains uncommon in under 50s.

Dr Marco Gerlinger, a scientist at the Institute of Cancer Research in London, told the science media centre: “These results are a call to action to raise awareness among staff in GP practices and hospitals to consider bowel cancer as a diagnosis when young people come to them with pain, changes in bowel habits or blood in their stool.”

It’s important for everyone to see their doctor about any changes to their body or poo habits that don’t go away. It’s likely that these symptoms will be something much less serious than cancer, but it’s best to get it checked out.

And the good news is no matter how old you are, keeping a healthy weight, eating more foods high in fibre, cutting down on alcohol and processed and red meat, and being more active can all reduce your risk of bowel cancer.

Katie Patrick is a health information officer at Cancer Research UK