Professor Giovannucci from Harvard University recently published a study in the BMJ on light to moderate alcohol intake and cancer risk. It is well known that heavy alcohol intake is associated with an increased risk of many cancers, including colorectal, female breast, oral cavity, pharynx, larynx, liver, esophagus, and, at higher risk, stomach, pancreatic, lung, and bladder cancers. While light to moderate alcohol intake is a very common lifestyle in the U.S. population, the relationship between light to moderate alcohol intake and cancer risk is not known. In addition, the association between heavy alcohol intake, especially ≥30 g/day, and cancer risk is significantly stronger among smokers than nonsmokers, and the role of smoking unrelated to alcohol is also understudied. The significant effect of alcohol on cancer risk in studies that included smokers may have been confounded by the effect of smoking, and therefore the findings may not apply to nonsmokers, who make up the majority of the US population. To assess the effect of light to moderate alcohol intake and smoking patterns on cancer risk, Professor 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. 47881 men, including 19269 women and 7571 men with cancer. Alcohol intake <30 g/day for men and <15 g/day for women in the study was defined as light to moderate alcohol intake, and light to moderate alcohol intake slightly increased total 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 light to moderate alcohol intake increased the risk in women regardless of smoking, especially for breast cancer. Professor Giovannucci analyzed several possible mechanisms by which alcohol intake increases cancer risk: acetaldehyde, the primary product of alcohol metabolism and its most toxic metabolite, is thought to be responsible for cancer. Alcohol can also induce cancer development by inhibiting DNA methylation and interfering with retinoid metabolism. Flora are involved in alcohol metabolism and can modulate the effects of alcohol genotoxicity on many diseases, especially in the colorectum and oral cavity where flora are abundant. Breast tissue may be more sensitive to alcohol than other tissues, which may be related to hormone levels.