Alcohol

ALCOHOL HAS BEEN used in most human societies for thousands of years. Nonetheless, alcohol consumption is associated with a host of social problems. Habitual or addictive overuse of alcohol is recognized as a disease. Long-term, excess alcohol consumption increases the risk of a number of serious chronic diseases. Whether moderate, occasional alcohol consumption has any untoward impact on human health is less clear. In fact, there is considerable evidence that low to moderate consumption of alcohol reduces the risk of cardiovascular disease. There are several cancers that can be attributed to excessive alcohol consumption (cancers of the mouth, larynx, pharynx, esophagus, and liver) and several others that are likely related to more moderate consumption (cancers of the breast, colon, and rectum).

Research on how alcohol consumption contributes to cancer risk is ongoing; the biological processes by which alcohol works to affect risk are not completely understood. It is clear, however, that the ways in which alcohol affects risk of different cancers are not uniform. The mechanisms by which alcohol consumption contributes to the risk of oral cancer may differ substantially from the ways in which it contributes to the risk of breast cancer, for example, likely in part because the lining of the mouth is in contact with alcoholic beverages while the breast would only be in contact with alcohol in the blood.

The possible mechanisms for the observed association of alcohol and cancer risk may involve the effects of alcohol on both the activation (the process whereby compounds are metabolized) and the clearance of carcinogens (cancer-causing compounds). Alcohol consumption may also affect nutrient intake and the ability of the body to use certain nutrients. For example, the intake of folate, a B vitamin, tends to be low in those who drink heavily. Furthermore, folate absorption, utilization, and metabolism are all adversely affected by heavy alcohol consumption. Therefore, some of the observed associations of alcohol and cancer risk may be also partly attributable to a low folate status. There is evidence that low folate levels may contribute to the development of some cancers. Another way that alcohol may act to promote cancer is by serving as a solvent for certain carcinogenic compounds, allowing them to enter tissues that might otherwise be protected. As a source of calories, alcohol can also contribute to obesity, which is clearly a risk factor for cancer at many sites. Alcohol may also affect metabolic processes, such as an impact on the concentration of hormones in the blood, which may in turn alter risk.

Alcohol is absorbed into the blood from the stomach and small intestine and then transported to the liver. Nearly 90 percent of alcohol metabolism occurs in the liver. Smaller amounts of alcohol are metabolized by the intestinal tract and by alcohol-metabolizing enzymes in other tissues.

There are genetic differences in the way that alcohol is absorbed and metabolized. There is evidence that genetic differences may explain part of the variation in drinking behavior, in alcohol metabolism, and in susceptibility to diseases associated with alcohol consumption such as cancer. It has been estimated that as much as 50 percent of the variability in the rate at which people metabolize and eliminate alcohol is related to genetic factors.

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