The study, of 50 countries between 2007 and 2017, found 27 had seen a rise in cases among younger people.
Many were richer nations but some were developing countries, the investigators, from the American Cancer Society, say.
“The increase in early-onset colorectal cancer is a global phenomenon,” one of the authors, Dr Hyuna Sung, said.
“Previous studies have shown this rise in predominately high-income Western countries – but now, it is documented in various economies and regions worldwide.”
And people needed to be aware of the early signs and symptoms, such as blood in poo.
Other symptoms can include:
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a persistent change in bowel habit – more frequent, with looser stools
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abdominal pain, discomfort or bloating
Cancer Research UK stressed rates in younger adults remained low, with about one in 20 bowel cancers in the UK diagnosed in under-50s.
Of the 44,100 new cases every year in the UK, about 2,600 were in 25-49-year-olds.
Spokesman Jon Shelton said: “The number of early-onset bowel-cancer cases for both men and women each year in the UK is very low, therefore it’s difficult to say for certain why we are seeing rates increasing at a faster rate in one group over another.”
But risk factors such as diet, obesity, alcohol and smoking could be involved.
“Improvements to detection meaning that people are diagnosed at a younger age could also be playing a key role in higher rates,” Mr Shelton added.
