It's the mystery plaguing doctors and scientists around the world. Why are cases of deadly bowel cancer rising so rapidly among young people?
Once associated with old age, each year the disease affects more Britons early in life.
Those under 49 today are now around 50 per cent more likely to develop bowel cancer than people of the same age in the early 1990s.
One of those struck down in recent years by the disease was broadcaster, journalist and campaigner Dame Deborah James, also known as Bowel Babe. Dame Deborah was diagnosed when she was 35. She died in 2022, aged 40.
The US, Australia and dozens of other countries are also experiencing the phenomenon - even as the number of patients over the age of 50 with the disease appears to be falling.
But some nations appear to be experiencing barely any increase in early-age bowel cancer cases. Experts say that, in many cases, this could be down to poor data-keeping, not to mention missed diagnoses in developing countries.
However, closer to home there are rich, Western nations with markedly fewer young people developing this disease, which experts say cannot be put down to inaccurate figures.
In Austria, bowel cancer cases in under-50s have only risen around 12 per cent since the early 1990s - just over a fifth of the UK's increase.
And data suggests that this increase is only in men. There has been no discernible rise in young Austrian women getting bowel cancer.
A similar story is seen in Italy, where studies suggest there has only been around a 13 per cent rise over the same time period.
Spain, meanwhile, has barely registered any change in its early-age bowel cancer diagnosis and this has only occurred among those aged 20 to 29. Spain’s young are half as likely to develop bowel cancer as those in the UK.
Experts agree that, in all these countries, early-age bowel cancer is on the rise. But the significant variations in the size of this increase is something researchers are increasingly studying with interest.
'The difference in bowel cancer diagnosis rates between countries is something that requires close attention,' says Prof Sarah Berry, a nutritional science expert at King's College London, who is leading a £20 million study, called Prospect, hoping to solve the mystery of these rising numbers.
'Your diet, lifestyle, prescription drugs and exposure to pollution will all vary depending on the country you are brought up in. It's possible that, by looking at these differences between nations, we can pinpoint what's behind this rise in cases.'
Some experts already suspect that is why young people in countries such as Austria, Italy and Spain are less likely to get bowel cancer. Moreover, they argue that, in many cases, the differences are down to lifestyle habits that Britons can adopt today.
First though, it's important to explain exactly what is bowel cancer - and who is most at risk. Every year, around 44,000 people are diagnosed with bowel cancer in the UK. The disease, also known as colorectal cancer, kills around 17,000 over the same time period.
'The difference in bowel cancer diagnosis rates between countries is something that requires close attention,' says Prof Sarah Berry, a nutritional science expert at King's College London, who is leading a study hoping to solve the mystery of these rising numbers.
Obesity, lack of exercise and alcohol have all been shown, over time, to raise the risk of the disease.
And, until recently, all research suggested the chances of developing bowel cancer rises with age.
For this reason, the NHS screens those between 50 and 74 for bowel cancer. This involves a biannual at-home poo test, called a faecal immunochemical test (FIT).
It looks for hidden blood, a common indicator of bowel cancer or polyps - abnormal growths in the bowels at risk of becoming cancer.
If the test spots blood in the stool, patients are invited for a colonoscopy, a procedure which involves inserting a thin, flexible camera into the anus to inspect the bowels for any signs of cancer.
At present, despite the rising number of bowel cancer cases in young people, the NHS has no plans to lower the age at which it screens patients for the disease.
Under-50s are not offered a FIT or colonoscopy unless they have bowel cancer symptoms or rare genetic mutations that put them at a heightened risk of the disease.
Until recently, all research suggested the chances of developing bowel cancer rises with age.
But in Austria, experts say it is far easier for younger patients to access bowel cancer screening - which may, in part, explain its lower rates of early-age disease. 'We offer colonoscopies to younger people,' says Dr Monika Ferlitsch, an internal medicine expert at the Medical University of Vienna.
'If someone is diagnosed with bowel cancer, we would often then ask their close family members if they would also like to be checked, regardless of age.
By doing this, we find more bowel polyps before they have a chance to become cancerous and remove them. We also have big advertising campaigns encouraging people to get colonoscopies, so lots of people take up the offer.'
UK cancer experts agree that there is a lot that can be learned from Austria. 'Austria has a terrific health system and this is another example of that,' says Prof Thomas Powles,director of Bart Cancer Centre and visiting professor Medical University Vienna.
'The UK relies on standardised national bowel screening programme,having hard-and-fast rules about who can get checked.But in Austria;if your GP thinks you need colonoscopy you'll get referred one regardless age.'
'Most European countries don't have screening programmes and their cancer survival rates are better than ours.'
However, experts say earlier testing is just one reason that Austria appears to be avoiding the worst of the early-age bowel cancer crisis - another is diet.
Studies show that Austrians,on average,consume far less ultra-processed food and drink than UK.These are items containing artificial ingredients not found home kitchens.
Examples include processed meat,chocolate,breakfast cereals,ready meals,store-bought sauces and margarines.Ultra-processed drinks include soft drinks,diet soft drinks,milkshakes and yoghurt drinks.
According to a review published in the medical journal Springer Nature in 2021,ultra-processed ingredients make up about 40 per cent of the British diet—one of the highest levels in Europe.
Meanwhile,ultra-processed ingredients account for just 30 per cent of the Austrian diet;consumption of these artificial products there has also fallen by roughly 13 per cent over past 15 years—the sharpest decline on continent.
Experts say that ultra-processed ingredients are one of the most likely causes of the rise in early-age bowel cancer cases. 'It's already known that patients who have an unhealthy diet high in processed meats and sugary drinks are more likely to get bowel cancer,' says Prof Berry.
'There is also some evidence that additives found in ultra-processed foods could inflame the bowel and raise the risk of cancer. We don't know that for certain but it's something that needs to be investigated.'
Experts say this difference in diet could also explain why Spain and Italy have such low rates of early-age bowel cancer. Just 13 per cent of the Italian diet and 25 per cent of the Spanish is made up of ultra-processed ingredients.
Experts also point to low fibre intake as a possible reason why such a significant number of young Britons are developing bowel cancer. Studies show the nutrient - found in root vegetables, seeds, nuts and wholegrain bread - is crucial for good bowel health. Research shows that for each additional 10g of fibre per day people consume, they reduce their risk of bowel cancer by 10 per cent.
'A high fibre intake really decreases your risk of bowel cancer,' says Prof Berry. 'It can protect the gut from damage caused by things like processed meat.'
But Britons,on average,consume far less fibre than other European nations—around 19g per day.
By comparison,italians have about 25g and spain 26g.
Crucially,experts say our poor diet is a relatively recent phenomenon which would explain why bowel cancer in young is now rising.'The British diet was fairly healthy until around the Eighties and Nineties—which is when we start to see this rise in colorectal cancer cases,' says Prof Bernard Corfe,a nutrition expert working at Newcastle University.
'After the Second World War,Britons usually had low sugar,low calorie diet;particularly when rationing still in place.'
'Later in century,we were relatively early adopters fast food compared rest Europe;which is perhaps why rates early-age bowel cancer higher.'
But,increasingly,youth across Europe eating worse;which would explain Italy Spain seeing numbers rise too.'
But for young patients themselves,the cause of their bowel cancer is less clear.
Charlotte Rutherford was 25 when she was diagnosed with the disease.The charity worker from Bristol began to experience severe stomach pains,changes in her bowel habits and vomiting after meals.Yet when she went to a GP,the problem was put down to indigestion and she was given heartburn tablets.
She was eventually diagnosed in December 2020 when her symptoms worsened and friends took her to hospital.Doctors found a tumour had obstructed Charlotte’s bowels.Surgery to remove the growth was a success.
However,it returned in 2023 in her lungs - meaning she required a second operation.
Thankfully,charlotte - now an ambassador for charity Bowel Cancer UK - is cancer free but says she still does not understand why she developed the disease.
'There’s no history of cancer in my family and while I drank in my 20s and ordered the occasional takeaway I’d say I was healthy and took good care of my body,' she says.
'I often wonder whether it’s the chemicals in our food but there’s no way to know.'