Time course and metabolism are important factors

According to National Institute on Alcohol Abuse and Alcoholism (NIAAA) scientists, existing epidemiologic evidence supporting the relationship between moderate alcohol consumption and breast cancer risk needs further study.   

“Understanding how and when alcohol consumption increases breast cancer risk is important for a full understanding of how moderate alcohol drinking impacts women’s overall health,” says first author Philip J. Brooks, Ph.D., program officer in the NIAAA Division of Metabolism and Health Effects.

To help women understand alcohol’s health effects, scientists at NIAAA analyzed recent epidemiologic studies of alcohol and breast cancer, in the context of the current understanding of the time course and molecular basis of human carcinogenesis.  Their analysis, which underscores the importance of accounting for time and drinking patterns when considering  alcohol’s health effects, appears as an online commentary in Alcoholism: Clinical and Experimental Research.

Recent epidemiologic evidence has associated even moderate alcohol consumption by women – no more than one drink per day -- with a 10 percent increase in breast cancer risk compared with non-drinking women. Other epidemiology and laboratory studies have consistently associated low to moderate alcohol intake with reduced risk for cardiovascular problems and other health benefits.

“This commentary is an important contribution to ongoing discussions about the health effects of moderate alcohol consumption,” says Kenneth R. Warren, Ph.D., NIAAA acting director.

Research into consistent low-level drinking may not account for the effects of large amounts of alcohol consumed at any one time.  

Some of the largest epidemiologic studies of alcohol and breast cancer risk involved asking middle-age postmenopausal women about their current alcohol consumption, then assessing breast cancer diagnoses over the next five to 10 years.

Since in most cases it takes roughly 20 years or more to go from a normal cell to a clinical diagnosis of cancer, Dr. Brooks maintains that the breast cancers diagnosed in these women could not have been caused by the alcohol they reported drinking at the beginning of the study.

“One possible explanation is that lifetime drinking, including heavy drinking earlier in life, increases breast cancer risk, consistent with several earlier epidemiologic studies,” says Dr. Brooks. “Another possible explanation is that some of the women had undiagnosed breast cancers at the time that the study began, and that alcohol drinking increased the probability of breast cancer diagnosis, perhaps by making the tumors grow faster.”  

A significant problem with alcohol and breast cancer studies, he says, has been that people tend to report less alcohol than they actually consume. As a result, such studies can overestimate the effect of a given amount of alcohol on breast cancer risk.  Another limitation of these studies is the lack of information about drinking patterns.

“There is a major difference between having several drinks on a single day and nothing on others versus consistently having one drink per day,” says Dr. Brooks.  “Binge-type drinking -- four or more drinks per occasion – on some days and not drinking on others does not average out to moderate drinking.  Having multiple drinks in the same sitting will result in higher blood alcohol levels than from a single drink, which can trigger a different type of alcohol metabolism leading to DNA damage. Notably, a recent epidemiologic study from Harvard found that women who reported binge-type drinking had higher breast cancer risk than those who did not.  More studies of this type would be valuable, since binge drinking by young women is on the rise.”

The most important point, says Dr. Brooks, is that we need to consider both time course and drinking pattern in relating alcohol drinking to breast cancer risk.

“In view of our lack of understanding of how and when alcohol consumption impacts breast cancer risk, and the documented health benefits of moderate alcohol consumption, it is not clear that stopping drinking would benefit the overall health of postmenopausal women who are moderate drinkers,’’ Dr. Brooks says. ``In contrast, based on our understanding of alcohol metabolism, as well as recent epidemiologic data, binge drinking by younger women could increase the risk of breast cancer later in life. Binge drinking is unhealthy for anyone, and the possibility of increasing breast cancer risk is another reason for women in particular to avoid binge drinking.”