Doctors have urged younger adults not to panic after an analysis linked low readings of two routine enzymes with a higher likelihood of young-onset colorectal cancer being diagnosed around the time of first screening.

Epic Research reported on 9 September 2026 that adults aged 18 to 44 with pre-screening AST below 14 U/L had a 65 per cent higher likelihood of early-onset colorectal cancer, and those with ALT below 14 U/L a 68 per cent higher likelihood, against values of 14 to 29 U/L. Screening advice is unchanged.

The Finding That Cut Against Usual Practice

The Cosmos study covered 11,469 US adults aged 18 to 44 who had a first colorectal cancer screening between January 2017 and March 2025 and at least one AST or ALT result in the three years before.

People with prior cancer, inflammatory bowel disease, Lynch syndrome, a family history of colon polyps or pregnancy were excluded. Cases found within a year of screening were matched with up to four screen-negative controls.

An AST of 30 U/L or above was tied to a 22 per cent lower likelihood of diagnosis and an ALT of 30 U/L or above to a 29 per cent lower likelihood.

Rising AST over three years was linked to a 27 per cent lower likelihood and rising ALT to a 26 per cent lower likelihood. Falling values showed no link.

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Why Clinicians Say the Numbers Are Not a Test

Kersten Bartelt, a nurse and researcher at Epic Research, said 'the direction was a little counterintuitive' because clinics usually watch for high liver enzymes.

She said nothing in the work suggests changing AST or ALT would change cancer risk. Low readings can mark reduced muscle mass or poor nutrition.

Dr Daniel Sussman of the University of Miami's Sylvester Comprehensive Cancer Center said the levels called low would generally be regarded as normal. The analysis has not been peer reviewed.

A UK Biobank cohort had earlier found inverse links between circulating ALT and AST and colorectal cancer risk.

Screening Ages Stay the Same in Britain and America

NHS bowel cancer screening in England is offered every two years to people aged 50 to 74, with home FIT kits posted to those registered with a GP.

People aged 75 or over can request a kit. The American Cancer Society still advises average-risk adults to start colorectal cancer screening at 45.

US data cited by the research team have shown colorectal-cancer incidence among adults aged 20 to 49 rising by roughly 3 per cent a year during a recent period. About 100 cancers a week were found through the NHS programme in 2024–25.

Rectal bleeding still warrants a GP visit at any age. The finding is an association and does not prove that low AST or ALT causes bowel cancer. The researchers and an outside gastroenterologist said a single low AST or ALT result should not be treated as a reason for early colorectal-cancer screening.

The NHS still posts FIT kits in England, and US guidance still starts routine checks at 45 for average risk.

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