People who drink alcohol regularly significantly increase their risk for rectal cancer, but the relative risk is less if wine accounts for one third or more of the weekly consumption, according to an article in the May issue of Gut.

The Danish population study involved more than 29,000 Danish men and women ages 23 to 95 years. Their weekly intake of beer, wine, and liquors was assessed, as well as colorectal cancer risk factors such as smoking, weight, and exercise habits. Men were more likely than women to be heavy drinkers, and heavy drinkers were more likely to smoke and to weigh more than light drinkers.

During a monitoring period of almost 15 years, 411 cases of colon cancer and 202 cases of rectal cancer were reported. Statistically, alcohol had little influence on the risk for colon cancer, but there was a clear association between alcohol and risk for rectal cancer. People who drank more than 41 units of alcohol per week had 2 times the risk of developing the disease as people who did not drink alcohol.

Additional analysis showed that the type of alcohol consumed had a significant bearing on rectal cancer risk. People who drank 14 or more units of beer or liquor per week were over 3.5 times as likely to develop rectal cancer as nondrinkers. However people who consumed the same total amount but whose intake was roughly one third or more of wine were less than 2 times as likely to develop the disease.

The authors noted that wine drinkers tended to be better educated and to exercise more than drinkers of beer or distilled liquors, so there could be contributions from other healthy lifestyle factors in determining observed cancer risk.

The authors did not see any obvious reasons why alcohol would be more damaging to the rectum than the colon but thought that the protective effect of wine is most likely due to resveratrol, a chemical found in grapes and wine that inhibits cellular processes involved in the growth of cancerous cells.