it may contain toxic substances, such as nitrosamines and polycyclic aromatic hydrocarbons, that alter DNA; and alcohol may in other ways compromise nutritional status and increase susceptibility to cancer (World Cancer Research Fund and American Institute for Cancer Research, 1997).
More than 40 studies have evaluated the relationship between high levels of alcohol intake and liver cancer. Although these studies did not use a standard definition of heavy drinking or even the same reference groups (nondrinkers versus the entire population), a positive association has been observed across a variety of study designs and populations (World Cancer Research Fund and American Institute for Cancer Research, 1997). Unlike most other cancers, liver cancer is associated only with the heavy persistent type of drinking characteristic of alcoholism, with its related chronic liver damage. Neither light nor moderate drinking increases liver cancer risk.
More than 25 studies have shown that alcohol increases breast cancer risk, most likely by raising the level of estrogen in the bloodstream or making the breast more vulnerable to carcinogens (Smith-Warner et al., 1998). A randomized feeding trial indicated that estrogen levels are increased when women consume even low levels of alcohol on a regular basis (Reichman et al., 1993).
The dose-response relationship between alcohol and breast cancer risk is best demonstrated in results from an analysis of data pooled from six prospective studies (Smith-Warner et al., 1998). In that analysis, women’s risk of breast cancer rose by 7 percent for every 10-g increase in daily alcohol consumption. The association did not differ substantially by type of alcoholic beverage consumed. Because breast tissue may be particularly vulnerable during adolescence and early adulthood, researchers have speculated that alcohol consumption during these time periods might be more harmful than alcohol consumption later in life (Colditz and Frazier, 1995), but to date, studies on this topic have been inconsistent (Harvey et al., 1987; Young, 1989; Garland et al., 1999).
Although the results are not entirely consistent, the majority of studies support an association between alcohol intake and an increased risk of colorectal cancer in both men and women (Giovannucci and Willett, 1994). Moreover, alcohol consumption is related to an increased risk of colorectal