By Dr. Mark Levine, the Doc with Pink Tights
I have to begin by confessing that I have a bias: I love a good wine and I collect Italian wines.
For many years there has been a controversy about alcohol consumption and the risk of breast cancer. A number of research studies have reported an association (link) between alcohol consumption and the development of a number of cancers including oral cavity (mouth) and pharynx (throat), esophagus, liver, breast, and colon cancers.
Such reports, even though they are published in the scientific literature, catch the attention of the media and not infrequently a story reporting that “alcohol causes breast cancer” is picked up by television, radio, or newspapers. A recent example of this was when the American Society of Oncology (which I am a member of) published a special article entitled “Alcohol and Cancer: A Statement of the American Society of Clinical Oncology” in November 2017. This article was quoted widely by the media and you may have read about it.
The scientific term for a process where we look for a cause and effect relationship between exposure to a factor and an illness like cancer is called causation. When you come across a statement like “alcohol causes breast cancer,” how do you determine whether there is truly a relationship?
What criteria do I look for?
- Is there an association reported in the scientific study? Typically, the type of study is called a case-control study in which cases of cancer are matched to control patients without cancer. Then the researcher determines the amount of alcohol cases and control have consumed over a period of time. The rate of alcohol consumption in the cases is compared to the rate in the controls to give a statistic called a relative risk.
- Is there a dose response relationship? In other words, as the amount of alcohol consumption increases the risk of cancer increases.
- Is there a biologic explanation?
What happens if I apply these criteria to alcohol and breast cancer?
- Association: One study carefully examined 118 studies examining the relationship between alcohol and breast cancer. The relative risk for heavy drinkers compared with non-drinkers and occasional drinkers was 1.61 for breast cancer (1.61 means that people who were heavy drinkers were 1.6 times more likely to develop breast cancer than non-drinkers). Heavy drinking was defined by more than 450 g per day of alcohol. Sometimes you will see this stated as a 60% increase in the risk of breast cancer.
- Dose-response Relationship: The relative risks for a non-drinker was 1.0; light drinker, 1.04; moderate drinker, 1.23; and heavy drinker, 1.61.
- Biologic Explanation: Ethanol is eliminated from the body by its oxidation ﬁrst to acetaldehyde and then to acetate. Ethanol per se is not mutagenic, but acetaldehyde is carcinogenic and mutagenic, by binding to DNA and protein. Also, alcohol drinking affects circulating concentrations of androgens and estrogens, which is a pathway of particular relevance to breast cancer.
What does a relative risk of 1.61 mean for me?
Suppose you are 50 years old. Your risk of developing breast cancer in the next 10 years is 2.3%. If you have been a heavy drinker, then your absolute risk of developing breast cancer in the next 10 years is 1.61 x 0.023 = 3.7%. Is an approximate absolute 1 % increase in a risk of developing breast cancer a lot? The answer is in the eyes of the beholder. A 1.6 increase in relative risk translates into a small increase in absolute risk.
ABSOLUTE RISK OF BREAST CANCER IN U.S. WOMEN BY AGE
Current Age (years)-Absolute Risk of Developing Breast Cancer in the Next 10 Years
20-1 in 1,667 (0.06%)
30-1 in 222 (0.5%)
40-1 in 68 (1.5%)
50-1 in 43 (2.3%)
60-1 in 29 (3.4%)
70-1 in 25 (4.0%)
It is likely that heavy alcohol consumption is associated with a small increase in the risk of developing breast cancer. It also has other impacts on health. The risk needs to be interpreted into something meaningful for you. I tell my patients when asked “everything in moderation.” By the way, there is no evidence that if you have breast cancer, alcohol will make it grow.