Alcohol consumption within the daily responsible guidelines of 2-3 units for women and 3-4 for men does not increase the risk of colorectal cancer.
Epidemiological studies have suggested that excessive alcohol intake increases colorectal cancer (CRC) risk. However, findings regarding tumour subsites and sex differences have been inconsistent.
Researchers investigated the prospective associations between alcohol intake on overall and site- and sex-specific CRC risk. Analyses were conducted on 579 CRC cases and 1996 matched controls nested within the UK Dietary Cohort Consortium using standardised data obtained from food diaries as a main nutritional method and repeated using data from food frequency questionnaire (FFQ).
Compared with individuals in the lightest category of drinkers (> 0- < 5 g per day), the multivariable odds ratios of CRC were 1.16 (95% confidence interval (95% CI): 0.88, 1.53) for non-drinkers, 0.91 (95% CI: 0.67, 1.24) for drinkers with 5- < 15 g per day, 0.90 (95% CI: 0.65, 1.25) for drinkers with 15- < 30 g per day, 1.02 (95% CI: 0.66, 1.58) for drinkers with 30- < 4 5 g per day and 1.19 (95% CI: 0.75, 1.91) for drinkers with >/= 45 g per day. No clear associations were observed between site-specific CRC risk and alcohol intake in either sex. Analyses using FFQ showed similar results.
The authors concluded that there was no significantly increased risk of CRC up to 30 g per day of alcohol intake within the UK Dietary Cohort Consortium. 
Source: Alcohol intake and risk of colorectal cancer: results from the UK Dietary Cohort Consortium. Park JY; Dahm CC; Keogh RH; Mitrou PN; Cairns BJ; Greenwood DC; Spencer EA; et al. British Journal of Cancer. Published early online 20 July 2010.