Breast Cancer & Alcohol: How Much is Safe?

Breast Cancer & Alcohol: How Much is Safe?
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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. I’ve also previously addressed the pros and cons in Alcohol Risks vs. Benefits.

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.

Images thanks to ondrej.lipar / Flickr

  • Melissa

    Dr. Gregor, This is an invaluably illuminating observation. It seems to implicate not only mouthwash, but also alcohol-based herbal tinctures–even those that purport to combat cancer or improve immunity. Do you have any observations about the “cost-benefit analysis” of such tinctures that may offer beneficial, alcohol-soluable compounds, but do so in a medium that is potentially cancer-inducing? Does this study suggest that we should avoid putting any alcohol in our mouths? Many thanks.

  • Dawggirl

    wait a minute! I thought we all understood that the only reason alcohol showed anything positive for heart disease was due to the resveratrol?? And of course, what came next was the fact that there are many other plant foods which offer us even higher levels of resveratrol (above that found in red wine), therefore, there is no reason to listen to the wine industry’s selective studies on benefits of wine?? I sure get tired of this endless discussion which never mentions the tired myths, especially when: 1.) right now, in America, we have the highest uptick in alcohol abuse that has occurred in a century; 2.) the drinking habit which progresses into end-stage alcoholism during late life (alcoholism is a progressive illness – the definition of disease is that it progresses!) is manifesting at a phenomenal rate among the oldest Boomers – those who are about 60-70, who of course have other precipitating factors destroying their livers already inc past drug abuse history, Agent Orange exposure, and multiple prescribed maintenance and interventional pharmaceuticals which we are now finding destroy our heart, brain, immune systems, livers, kidneys, etc. Being a 67 year old former substance abuse counselor currently surrounded by relatives and friends who are dying of their daily medicine drink + pills, I cannot wait for the Rest of The Story to catch up with us all.

    • Darryl

      Actually, moderate alcohol appears to have positive effects in heart disease quite independent from resveratrol (which is absorbed in near negligible quantities). Here’s a curent review of epidemiological evidence and proposed mechanisms:

      Krenz, Maike, and Ronald J. Korthuis. “Moderate ethanol ingestion and cardiovascular protection: From epidemiologic associations to cellular mechanisms.” Journal of molecular and cellular cardiology 52.1 (2012): 93-104.

      Some effect of moderate alcohol include:
      • increased HDL cholesterol
      • decreased fibrinogen (a blood clotting factor)
      • reduced oxidative stress
      • improved insulin sensitivity
      • lowered blood pressure
      • vasodilation via increased eNOS expression
      • increased tolerance to ischemia/reperfusion

      The most interesting cellular mechanism for me is induction of ALDH2, which both clears acetaldehyde, the initial metabolite of alcohol, and also other reactive carbonyls resulting from oxidative stress, including lipid peroxidation and early glycation products. This mechanistic work is important, as it offers potential for obtaining the vascular and (overall) cancer preventative effects associated with moderate alcohol use without the associated acetaldehyde damage (especially at higher intakes) and sociobehavioral consequences. So far, there are only a couple of novel compounds that appear to activate ALDH2 directly, but a least one dietary compound does indirectly. If it does so via Nrf2, then that both clarifies how Nrf2 activation prevents ischemia/reperfusion injury and offers a mechanism of mimicking the effect of alcohol throug the many known dietary Nrf2 activators.

  • DH

    In these studies, teatotallers (alcohol abstainers) are invariably the referent group. But they are a pretty odd group, going against social norms, and represent, what?, 10-15% of the general population? They represent a collection of different groups – some for religious reasons (e.g. Muslims), some for health reasons (e.g. people on extremely healthy diets), some for other personal reasons (e.g. a remote history of alcoholism, successfully treated by abstention). Thus these people are probably quite different than those who consume up to 1 glass of alcohol per day.

    What is weird about this hypothesis of mine is that confounding does not adequately explain why there is a J curve for cardiovascular disease but no J curve, actually a linear relationship, with breast cancer. You would expect the confounding to go in the same general direction, even though CVD and breast cancer are two different entities. They tend to share common antecedents like obesity, smoking, sedentarism and dysglycemia.

    Hence while we will never get a randomized trial to sort this issue out, we can look to observational studies and the dichotomy they present between CVD outcomes on the one hand, and cancer outcomes on the other. This actually suggests specificity for cancer, thereby fulfilling one of Bradford-Hill’s strongest criteria for causality. Very interesting, indeed! Thanks Dr G!

    • Darryl

      There is a J-curve for alcohol and all-cancer mortality. Low-dose alcohol appears to induce antioxidant response element and heat shock response proteins (so like cruciferous vegetables, alcohol may be a hormetin). But breast cancer is different – aside from breast being one of few tissues that in health cyclically proliferates, and is hence epigenetically primed for cancer initiation, I’m not sure why the dose response to alcohol differs from other tissues.

      • DH

        Good kibbitzing with you; your knowledge base is phenomenal.

        I wasn’t aware that low amounts of alcohol was actually chemopreventive in terms of cancer health for most non-breast cancer tissues. It is unusual for a substance, perhaps even one as complex as an alcoholic beverage, to have a bimodal effect on malignancy such that it retards cancer in one organ system/tissue type but promotes it in another. More likely either the breast cancer studies are wrong or the meta-analysis is wrong and the findings in nature are probably more aligned. Then again, cigarette smoking only affects certain body tissues and does not uniformly cause cancer in every tissue bed exposed to its carcinogenic constituents – unlike, say, ionizing radiation or many types of chemotherapy.

        • Darryl

          Genetic variations in alcohol metabolism probably confound attempts to establish risk curves. There was an interesting study that compared alcohol dehydrogenase genotypes with alcohol induced breast cancer risk. Those who metabolized alcohol to acetaldehyde quickly were at much higher risk. I haven’t found similar studies on aldehyde dehydrogenase 2 (which clears acetaldehyde) and breast cancer, but heavy drinkers with less active ALDH2 are at much higher risk of stomach cancer. If the acetaldehyde, which forms DNA adducts, is the main carcinogenic agent, then those expressing fast ADH/slow ALDH2 would be a much higher risk from a given alcohol intake than those with slow ADH/fast ALDH2 genotypes.

          Incidentally, more active forms of ALDH2 (which reduce the severity of hangovers and flushing) are strongly associated with alcoholism. Still, the morning-after may be a useful gauge of how much genetic damage one is doing.

          • DH

            Fascinating! But your previous link is not directing to a known website and I would love to read it — viz. “This meta-analysis found a J-curve for alcohol and all-cancer mortality.”

          • Darryl
          • DH

            Darryl, I had a few more questions about aspirin dosing for chemoprevention. 1) Would it work with ultra-low dosing – i.e. half of an 81 mg enteric coated tablet per day (I believe there is one trial – Dutch TIA – which compared 30 mg with 300 mg and found a non-significant but large (if it had been better powered) risk reduction with the higher dose; this is in Rothwell’s meta-analysis); 2) would a diet rich in fruits and vegetables be sufficient for chemoprevention – i.e. it is likely that ASA’s benefit in all those trials was on top of a very poor diet, since most of the patients had already demonstrated a tendency to fall into vascular disease.

            If I had to do it, I would consider taking half an enteric coated ASA 81 mg tablet.

  • Stephen Albers

    I don’t consider myself an egotistical person. But in this case I’m allowing myself an increase in my smugness coefficient since I’ve always been deeply suspicious of the effects of alcohol consumption. Maybe watching my grandfather die of liver cirrhosis – essentially starving to death – had something to do with it. Beyond that, considering alcohol not a food but either a chemical or drug also helps. Then realizing it is one of two consumables of zero nutrient density: alcohol and sugar really helps. Confusion factors like resveratrol and heart disease protection never dissuaded me. To me, the record is clear: there is no benefit to consuming alcohol and considerable risk.

  • Boycey95

    The article states, “The bacteria in our mouths appear to oxidize alcohol into this acetaldehyde carcinogen, which we then swallow”.

    So if you use (non-alcoholic) antiseptic mouthwash before consuming an alcoholic beverage, will the amount of carcinogen produced and therefore swallowed be significantly reduced?

  • Dawn D’Haeze

    Question: Have there been studies on moderate to heavy alcohol consumption among very healthy people? Just curious if healthy eating (plant based) and moderate exercise would lesson or counteract the negative effects. Thanks!