More than 250,000 people are being recruited for a major study into the mystery of why bowel cancer rates are soaring in adults under 50.
The disease was once found mainly in older adults but is increasingly being diagnosed at a younger age.
Experts said early-onset bowel cancer has increased ‘substantially’ around the world since 1990, and the UK has one of the fastest rising rates.
It is not clear what is driving the rise, though obesity is thought to be a potential factor.
Experts at King’s College London and health science company Zoe want 250,000 adults aged 18 and over across the UK to take part in the study.
The trial, known as Prospect-UK, will track people over time, looking at diet and lifestyle factors.
Participants will complete online questionnaires on their diet, lifestyle, environment, health and other factors.
They will also be asked for their information to be linked to their electronic health records so researchers can track cancer cases.
A small group will be asked to complete more detailed diet diaries and provide blood and stool samples.
Professor Sarah Berry, chief investigator of the trial and professor of nutritional sciences at King’s College London, said: ‘Over just a few generations our lifestyles, diets and environments have changed dramatically.
‘But we don’t know which of these changes are increasing people’s risk of bowel cancer or which ones could help reduce it.
‘We urgently need large-scale, long-term data to uncover the true causes of early-onset bowel cancer.’
There are around 44,100 new cases of bowel cancer each year in the UK, with the highest incidence in people aged 85 to 89.
However, 2,700 cases a year are among people aged 25 to 49, with incidence rates in this age group rising by 62.3 per cent since the early 1990s, according to Cancer Research UK.
There were around 8 cases per 100,000 people in this age group in the UK in 1993/95, rising to 13 per 100,000 in 2018/21.
Dr Rosiered-Brownson Smith, study research associate at King’s College London, said: ‘Although rates of early-onset bowel cancer are rising, it remains relatively uncommon, which means we need large groups of people to take part in research to help us understand why we are seeing this worrying trend.
