This well-done analysis based on data from two very large cohort studies, the Nurses’ Health Study and the Health Professionals’ Follow-up Study, evaluated the association of alcohol consumption over many years with the risk of cancer. The authors conclude that men reporting an average intake of more than 15 grams of alcohol per day, but not less, have a significant increase in risk of alcohol-related cancers. In women, however, even the consumption of an average of 5.0 – 14.9 grams of alcohol per day (the equivalent of between ½ and 1 ½ typical drinks) was associated with a slight increase in total cancer risk, stated to be primarily from an increase in the risk of breast cancer. For both genders, there seemed to be a dose-response increase in risk of cancer with larger amounts of alcohol. At the same time, smoking was identified as an even more important risk factor than alcohol for these cancers.
Forum members considered this to be an important study presenting data that are of relevance to individuals and agencies providing advice regarding alcohol consumption. There is little question that heavy drinking markedly increases the risk of upper aero-digestive cancers, and no physician or agency advises people to consume in excess of the typical limits of no more than one or two drinks/day. Hence the finding in this study of an increase in some cancers among women (especially breast cancer) even for lighter drinking has implications for alcohol policy.
The Forum was disappointed that all dietary and other lifestyle factors that have been shown to increase the risk of cancer (data that are known to be available to these investigators) were not included in their report. Members were especially concerned that the net effects on health and mortality of light-to-moderate alcohol consumption were not commented upon in the paper. Given that the risk of the most common causes of death, especially cardiovascular diseases, are reduced by moderate drinking, it seems that the authors should have included data, or at least mentioned, the effects of alcohol on cancer mortality and, especially, on total mortality. It has recently been emphasized that cohort studies that report on only one outcome (in this case, cancer) but do not mention other outcomes that are affected by the same exposure, especially total mortality, do not present the full picture, and can lead to biased recommendations. The inclusion of such information from these cohorts could provide even more valuable data upon which to develop appropriate guidelines for alcohol use by individual patients and the public.
Reference: Cao Y, Willett WC, Rimm EB, Stampfer MJ, Giovannucci EL. Light to moderate intake of alcohol, drinking patterns, and risk of cancer: results from two prospective US cohort studies. BMJ 2015;351:h4238; doi: 10.1136/bmj.h4238