Background Alcohol consumption is one of the major risk factors of colorectal cancer (CRC). However, the mechanisms underlying this relationship are not fully understood, particularly the potential role of gut microbes.

Objective To study associations of alcohol intake with the gut microbiome and colorectal lesions among CRC screening participants. Of particular interest was the potential role of gut microbes in mediating the association between alcohol intake and colorectal lesions.

Methods Participants included fecal immunochemical test-positive women and men enrolled in the CRCbiome study, aged 55-77 years at inclusion. Intake of alcohol was assessed using a validated, semi-quantitative food frequency questionnaire. Integrating with shotgun metagenome based taxonomic and functional profiles, we studied associations with screen-detected colorectal lesions. The potential role of alcohol-associated gut microbes in mediating the association between alcohol intake and colorectal lesions was examined using causal mediation analysis.

Results Of 1,468 participants with dietary data, 414 were diagnosed with advanced lesions (advanced adenoma, advanced serrated lesions or CRC). Alcohol intake was positively associated with advanced lesions in a dose-dependent manner (ptrend = 0.008), with odds ratio of 1.09 (95% confidence interval, 1.00, 1.19) per 10 g/day increase. Compared to non-consumers, those consuming alcohol were characterized by a distinct microbial profile, manifested as modest, but consistent, shifts in α- and β-diversity, and differentially abundant bacteria (Log2 fold change (Log2FC) >0: B. finegoldii and L. asaccharolyticus; Log2FC <0: S. mutans, B. dentinum, C. symbiosum and E. boltae). A causal mediation analysis showed that 12% of the association between alcohol intake and advanced lesions was mediated by alcohol-associated gut bacteria.

Conclusions Alcohol consumption was associated with a distinct microbial profile, which partly explained the association between alcohol intake and advanced colorectal lesions.

Trial Registration The BCSN is registered at clinicaltrials.gov (National clinical trial (NCT) no. 01538550).

Dr. Mingyang Song serves as a consultant for Etiome Inc. The remaining authors declare no conflicts of interest.

his project would not have been possible without funding from the Norwegian Cancer Society (grant nos. 190179 and 198048), the Norwegian Cancer Societys umbrella organization for cancer research (Kreftforeningens paraplystiftelse for kreftforskning), the Research Council of Norway (grant no. 280667) and the South-Eastern Norway Regional Health Authority (grant nos. 2022067 and 2020056). The BCSN trial study was funded by the Norwegian Parliament (Norwegian national budget from 2011). The bowel preparation used for colonoscopy was provided free of charge by Ferring Pharmaceuticals. The funders of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

Both the BCSN and the CRCbiome study have been approved by the Regional Committee for Medical Research Ethics in South-East Norway (Approval no.: 2011/1272 and 63148, respectively). The BCSN is also registered at clinicaltrials.gov (Clinical Trial (NCT) no.: 01538550).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).

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I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable.

Yes

DNA sequencing data analyzed in this study are deposited in the database Federated EGA under accession code EGAS50000000170 (https://ega-archive.org/studies/EGAS50000000170). Per participant consent, submitted FASTQ files exclude reads mapping to the human genome. The data are available under restricted access due to the sensitive nature of data derived from human subjects. Processing of data from this study must comply with the General Data Protection Regulation (GDPR). Access can be obtained by following the procedure described here: https://www.mn.uio.no/sbi/english/groups/roungegroup/crcbiome/. Requests for data access can also be directed to Trine B Rounge, trinro@uio.no.