People who choose to drink may cite research on the "heart-healthy" effects of alcohol -- the association between moderate drinking and reduced risk for heart disease. But two recent research summaries indicate that drinkers need to take another finding into account: the link between alcohol and cancer.

Studies from two countries help summarize the association. One was conducted by researchers from the Institute of Medical Statistics and Biometry at the University of Milan in Italy and published in the journal Alcohol Research & Health (Vol 25, No. 4, 2001). The other is a research review included in the Tenth Special Report to the U.S. Congress on Alcohol and Health, published by the U.S. Department of Health and Human Services in 2000.

Both sources indicate that alcohol use can contribute to the risk of various cancers. These include colorectal cancer in men and women and breast cancer in women -- the most common and fatal forms of the disease (after lung cancer) found in developed countries.

By pooling the results of over 200 published studies, the Italian researchers discovered that drinking increases the risk of some cancers more than others. Most strongly associated with alcohol use were cancers of the oral cavity, pharynx, esophagus, and larynx. Lesser but significant links also existed between alcohol and cancers of the stomach, colon, rectum, liver, female breast, and ovaries.

There was also evidence for links between alcohol and pancreas, prostate, and endometrial cancers. However, these associations are weaker and still controversial.

Researchers concluded that the links between alcohol and cancer were "dose-dependent." That is, heavy drinkers -- people who consume more than four alcoholic drinks per day -- had the greatest cancer risk. But even people who drank moderately increased their risks. (The U.S. Department of Health and Human Services defines moderate drinking as a maximum of one drink per day for women and two for men.) This finding undermines the notion that there is a "safe" level of drinking-a level of alcohol consumption with no increased risk for cancer.

Research does not show that alcohol by itself is a carcinogen -- a substance that directly causes cancer. Instead, alcohol seems to accelerate the effect of known carcinogens.

Scientists don't understand how this takes place, though they offer some possible explanations. For example, long-term, heavy drinking commonly leads to cirrhosis of the liver -- a key factor in developing liver cancer. Heavy drinking can also increase the risk of infection with the hepatitis C virus, another cause of liver cancer.

Many drinkers also smoke, in effect using alcohol to enhance the carcinogens in cigarettes. In developed countries, 75 percent of cancers of the upper digestive and respiratory tract may result from the combined use of alcohol and tobacco.

Breast cancer -- which affects about one of every eight women in the U.S. -- offers more examples of how alcohol can promote cancer. For one, higher lifetime levels of estrogen are associated with increased cancer risk. Alcoholic drinks such as bourbon and whiskey contain phyto-estrogens, plant products that can mimic the effect of estrogen in a woman's body.

In addition, a diet low in fruits and vegetables has been associated with breast cancer. Women who consume heavy amounts of alcohol tend to eat the least amounts of these foods.

The key factor in any case is the amount of alcohol consumed, not the type of drink. It does not matter whether a woman drinks beer, wine or distilled spirits. Even one or two drinks per day can increase the risk of breast cancer.

Alcohol is just one factor in cancer risk, along with age, gender, family history, environment, and diet. Even so, current research underlines the risks of heavy drinking and offers findings relevant to anyone who wants to drink at any level.