Breast Cancer and Alcohol: How Much Is Safe?

Nearly 5,000 breast cancer deaths a year may be attributable to just light drinking (up to one drink a day).

The International Agency for Research on Cancer, the World Health Organization body tasked with collating the totality of evidence as to whether or not something causes cancer, has now concluded that alcoholic beverages—all alcoholic beverages—are to be considered carcinogenic to humans.

There has been convincing evidence that alcohol consumption increases the risk of breast cancer, but most of the data were derived from studies that focused on the effect of moderate or high alcohol intakes, while little was known about light alcohol drinking (up to 1 drink/day). A recent meta-analysis of studies that compared light drinkers to non-drinkers found a moderate but significant association with breast cancer, based on the results of more than 100 studies.

The researchers estimate that about 5,000 breast cancer deaths a year are attributable to light drinking, meaning nearly 5,000 women that died of breast cancer maybe wouldn’t have if they had stayed away from alcohol completely, leading to an editorial in the medical journal Breast that concluded “women who consume alcohol chronically have an increased risk for breast cancer that is dose dependent but without threshold.” No threshold means there’s apparently no level of alcohol consumption that doesn’t raise breast cancer risk at least a little. Any level of alcohol consumption appears to increase the risk of developing an alcohol-related cancer. For example, the Harvard Nurses’ Study found that even consumption of less than a single drink per day may be associated with a modest increase in risk.

Most recent research has focused on acetaldehyde, the first and most toxic alcohol metabolite, as the primary cancer-causing agent. The bacteria in our mouths appear to oxidize alcohol into this acetaldehyde carcinogen, which we then swallow. So even a single sip of alcohol may be harmful. A new study found that just holding a teaspoon of hard liquor in our mouth for 5 seconds results in carcinogenic concentrations of acetaldehyde—even if we don’t swallow. The exposure continues for at least 10 min after spitting it out.

No surprise then alcohol-containing mouthwash can offer a carcinogenic spike as well. Researchers conclude: “All in all, there is a rather low margin of safety in the use of alcohol-containing mouthwash. Typical use will reach the concentration range above which adverse effects are to be expected. Until the establishment of a more solid scientific basis for a threshold level of acetaldehyde in saliva, prudent public health policy would recommend generally refraining from using alcohol in such products.”

So why isn’t the same recommendation made for alcoholic beverages? Well, as the Harvard paper concludes, “individuals will need to weigh the risks of light to moderate alcohol use on breast cancer development against the benefits for heart disease prevention to make the best personal choice regarding alcohol consumption.” They’re talking about the famous J shaped curve (watch my 4-min video Breast Cancer and Alcohol: How Much is Safe? to check it out). While smoking is bad and more smoking is worse, and in general exercising is good and more exercise is better, for alcohol there appears to be a beneficial effect of small doses. A six-pack a day raises overall mortality, but so does teetotalling.

The #1 killer of women isn’t breast cancer, but heart disease, and a drink a day reduces the risk of heart disease. Why just reduce the risk of heart disease, though, when you may nearly eliminate the risk of heart disease with a healthy enough diet? See, for example, my video Eliminating the #1 Cause of Death. A plant-based diet that excludes certain plant-based (alcoholic) beverages may therefore be the best for overall longevity.

For more on this topic, please see my follow-up video Breast Cancer Risk: Red Wine vs. White Wine

The other mouthwash video I refer to in the above video is Don’t Use Antiseptic Mouthwash, part of a video series on improving athletic performance with nitrate-containing vegetables (if interested, start here: Doping With Beet Juice).

How else might one reduce breast cancer risk? Please feel free to check out:

-Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my videos for free by clicking here and watch my full 2012 – 2015 presentations Uprooting the Leading Causes of Death, More than an Apple a Day, From Table to Able, and Food as Medicine.

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