Norwegian study suggests alcohol may raise bowel cancer risk partly through changes in gut bacteria

03.05.2026 - A new Norwegian study has added to the evidence linking alcohol consumption with colorectal cancer development, while also exploring a possible biological pathway through the gut microbiome. The study, published in the European Journal of Nutrition, found that alcohol intake was associated with advanced colorectal lesions detected during bowel cancer screening, and that part of this association may be explained by alcohol-related changes in gut bacteria.

The researchers analysed data from participants in the CRCbiome study, which is part of the Bowel Cancer Screening in Norway pilot programme. The study included 1,486 people aged 55 to 77 who had tested positive for hidden blood in stool and underwent colonoscopy. Among them, 414 were diagnosed with advanced lesions. These included colorectal cancer, advanced adenomas, and advanced serrated lesions, which are benign growths with a higher risk of developing into cancer.

Alcohol intake was assessed through a validated food frequency questionnaire, and 947 participants also had detailed gut microbiome data available from stool samples. The study found a dose-related association between alcohol and advanced lesions. For every 10 grams of alcohol consumed per day, the odds of having advanced lesions increased by 9%. The association was seen even at moderate levels of consumption and appeared particularly strong among women in this study.

The researchers also found that people who consumed alcohol had a distinct gut microbial profile compared with non-consumers. Their analysis suggested that alcohol-associated gut bacteria mediated around 12% of the association between alcohol intake and advanced colorectal lesions. In other words, changes in gut bacteria may be one of several ways through which alcohol contributes to colorectal carcinogenesis.

Alcohol is already known to increase cancer risk through several mechanisms. Ethanol is metabolised into acetaldehyde, a toxic compound that can damage DNA. Alcohol may also affect genes, inflammation, immune responses and other biological processes relevant to cancer development. This study points to another possible pathway: alcohol may disturb the composition and function of bacteria in the gut, which could contribute to processes involved in bowel cancer development.

The authors stress that the findings should be interpreted with some caution. The study included only people with a positive stool blood test, which means the results may not apply directly to the whole population. The study design was also cross-sectional, so it cannot prove cause and effect. Still, the findings are consistent with the wider evidence that alcohol plays a role in the development of colorectal cancer.

The public health message remains clear. Alcohol is a preventable risk factor for colorectal cancer, and lower consumption means lower risk. This new study strengthens the case that alcohol can influence cancer development through several pathways, potentially including the gut microbiome.

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Source: Ane Sørlie Kværner et al., “Alcohol consumption and colorectal carcinogenesis: an exploration of the gut microbial pathway as a potential mediator”, European Journal of Nutrition, published 21 April 2026. DOI: 10.1007/s00394-026-03960-6.