Colectomy specimen containing an invasive colorectal carcinoma (the crater-like, reddish, irregularly-shaped tumor).

Drinking may be a cause of earlier onset of colorectal cancer. The evidence that alcohol is a cause of bowel cancer is convincing in men and probable in women.

The National Institutes of Health, the National Cancer Institute, Cancer Research, the American Cancer Society, the Mayo Clinic, and the Colorectal Cancer Coalition, American Society of Clinical Oncology and the Memorial Sloan-Kettering Cancer Center list alcohol as a risk factor.

A WCRF panel report finds the evidence "convincing" that alcoholic drinks increase the risk of colorectal cancer in men at consumption levels above 30 grams of absolute alcohol daily. The National Cancer Institute states, "Heavy alcohol use may also increase the risk of colorectal cancer"

One study found that "While there was a more than twofold increased risk of significant colorectal neoplasia in people who drink spirits and beer, people who drank wine had a lower risk. In our sample, people who drank more than eight servings of beer or spirits per week had at least a one in five chance of having significant colorectal neoplasia detected by screening colonoscopy.".

The EPIC study suggests that "people who drink 15 grams of alcohol a day– equivalent to about two units– have about a 10 percent increased risk of bowel cancer. Those who drank more than 30 grams of alcohol– equivalent to three to four units which is less than a couple of pints of strong lager– increased their bowel cancer risk by around 25 per cent."

A study found, "The proportion of patients with adenomas was 29.6% in abstainers, 22.1% in moderate drinkers, and 36.7% in heavy drinkers." It concluded "Consumption of less than seven alcohol drinks per week does not increase the risk of having a colorectal adenoma. We found evidence in this study that moderate alcohol consumption among long-term smokers may potentially decrease the risk of an adenoma compared to abstainers."

A Japanese study concluded, "One fourth of colorectal cancer cases in men were attributable to an alcohol intake of ≥23 g/day."

A study concluded that for every additional drink regularly consumed per day, the incidence of rectal cancer increases by 1 per 1000.