Bowel cancer rates are rising in young adults for no apparent reason, experts are warning.
Cancer Research UK says that although the disease still affects older people more, the rise in people under 50 in many countries is worrying.
England is one of the fastest growing countries, with an average increase of 3.6% per year, the researchers report in the journal Lancet Oncology.
Researchers say poor diet and obesity may be risk factors.
A study of 50 countries between 2007 and 2017 found that 27 saw an increase in cases among young people.
American Cancer Society investigators say many were rich countries but few were developing countries.
“The increase in early-onset colorectal cancer is a global trend,” said Dr. Hyuna Sing, one of the authors.
“Previous studies have shown this increase mostly in high-income Western countries – but now, it’s being documented in different economies and regions around the world.”
And people need to be aware of early signs and symptoms, such as blood in the poo.
Other symptoms may include:
- Persistent change in bowel habits – with more frequent, loose stools
- Abdominal pain, discomfort or bloating
Cancer Research UK emphasized that rates remained low in younger adults, with one in 20 bowel cancers diagnosed in the UK under the age of 50.
Around 2,600 of the 44,100 new cases in the UK each year were in people aged 25-49.
Spokesman Jon Shelton said: “The number of early-onset bowel cancer cases for both men and women in the UK each year is very low, so it is difficult to say for sure that we are seeing rapid increases in rates in one group. Why are you adding on the other.”
But risk factors such as diet, obesity, alcohol and smoking may be involved.
“Improved detection, which means people are being diagnosed at a younger age, may also be a key factor in the higher rates,” added Mr Shelton.
Dr David Robert Grimes, a biostatistician at Trinity College Dublin, said more research was needed.
“This finding is interesting — but we have to resist the urge to jump to conclusions, especially with conflicting and complex data,” he said.
“Although the headline may seem alarming in isolation, it could also mean that screening and better detection are allowing us to catch cancer earlier.”
Dame Deborah James, who died of bowel cancer aged 40, took to social media to share her experiences and urged people to “check their poo” and if they notice any irregular bowel movements. Get them tested.
The mother-of-two, known to many as Bowelbabe, also hosts BBC Sounds’ You, Me and the Big C podcast and is a Documentary film About living with illness.