Recently Prof. Giovannucci from Harvard University published a study in the BMJ on light to moderate alcohol intake and cancer risk. Heavy alcohol intake is known to increase the risk of many types of cancer, including colorectal, female breast, oral, pharyngeal, laryngeal, liver, and esophageal cancers, as well as the higher risk of stomach, pancreatic, lung, and bladder cancers. Whereas light to moderate alcohol intake is a very common lifestyle among the U.S. population, the relationship between light to moderate alcohol intake and cancer risk is unknown. In addition, the association of heavy alcohol intake, especially ≥ 30 g/day, with cancer risk is significantly stronger in smokers than in nonsmokers, and the role of smoking not associated with alcohol is similarly understudied. The significant effect of alcohol on cancer risk in studies that included smokers may have been confounded by the role of smoking, and therefore the findings may not be applicable to nonsmokers, who comprise the vast majority of the U.S. population. To assess the effects of light-to-moderate alcohol intake and smoking patterns on cancer risk, Prof. Giovannucci analyzed alcohol intake data from 2 prospective cohort studies of U.S. health professionals: the Nurses’ Health Study, which began in 1980, and the Health Professionals Follow-Up Study, which began in 1986 and included a total of 88,084 women and 47,881 men in 2010. A total of 88084 women and 47881 men were enrolled in 2010, of whom 19269 were women and 7571 were men with cancer. Alcohol intake of <30 g/day for men and <15 g/day for women was defined as mild to moderate alcohol intake in this study, which slightly increased the overall cancer risk in both men and women, and this effect was independent of smoking. For alcohol-related cancers, light to moderate alcohol intake increased the risk only in men who smoked and had no effect on non-smoking men, but in women, light to moderate alcohol intake increased the risk regardless of whether they smoked or not, especially for breast cancer. Prof. Giovannucci analyzed the mechanisms by which alcohol intake increases the risk of cancer, including the following possibilities: Acetaldehyde, the primary product of alcohol metabolism and its most toxic metabolite, is thought to be responsible for causing cancer. Alcohol can also induce cancer by inhibiting DNA methylation and interfering with retinoic acid metabolism. Flora is involved in alcohol metabolism and can modulate the effects of alcohol genotoxicity on many diseases, especially in the colorectal and oral cavity where flora is abundant. Breast tissue may be more sensitive to alcohol than other tissues, perhaps related to hormone levels.