A causative factor not listed in this paper directly is the increased consumption of ultra-processed foods. Indirectly, they do mention the rise of salt consumption which is linked to the increase of GI cancers in the young:
“(I)t is necessary to conduct prospective life-course cohort studies to explore the aetiologies of early-onset cancers. Encouraging a healthy lifestyle, including a healthy diet, the restriction of tobacco and alcohol consumption and appropriate outdoor activity, could reduce the burden of early-onset cancer. It is worth exploring whether early screening and prevention programmes for early-onset cancer should be expanded to include individuals aged 40–44 and 45–49, but further systematic studies and randomised trials are necessary to make a definitive determination.”
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