Dear Doctor: I just read about a study that says exercise cancels out alcohol’s higher risk of death from cancer. Is it possible that I can walk off the cancer risk of the cocktail I have each night after dinner? (For the record, my husband is sure that you’re going to say no.)
Dear Reader: While we commend your creative thinking, your husband has guessed right. In our opinion, you can’t depend on added exercise to cancel out the increased risk of cancer that can be caused by alcohol consumption. It’s not that we think the study itself is wrong. It’s the way the results have been interpreted in some news stories — as cause and effect — that is, at best, misleading.
Let’s start from the beginning.
Researchers in England looked at a decade of medical data collected from 36,370 women and men, all 40 or older. They sorted the study subjects by how much alcohol they consumed and by how much they exercised.
Not surprisingly, they found a statistical link between "hazardous drinking" and an increased risk of death from all causes, including cancer. In this study, hazardous drinking was defined as 8 to 20 servings of alcohol per week for women, and 21 to 49 servings of alcohol for men.
Then the researchers included exercise as a variable in their calculations. They found that among people who spent at least 150 minutes per week doing moderate aerobic activity, like a brisk walk, the mortality rate due to cancer dropped. This proved to be true even among the heavier drinkers, as long as they exercised.
On its face this seems to suggest, as many news reports went on to state, that exercise can cancel out the elevated risk of cancer due to drinking. But — and this is crucial — this is what’s known as an observational study. That means the study is based solely on data collected from the same subjects over a period of time.
While studies like these are useful for pointing out the existence of certain patterns based on the information at hand, they can’t be used to prove cause and effect. The level of exercise among the drinkers is just one among countless variables that can play a role in whether someone goes on to get cancer. These variables include genetics, family history, diet, environmental causes, and levels of stress and anxiety, to name just a few. Even how forthcoming and reliable the study’s subjects were in self-reporting their drinking and exercise habits would have an impact on the outcome.
That said, what this study does do is add to the significant body of existing evidence that exercise plays a role in good health. Exercising may not automatically equal risk-free drinking, but people who exercise regularly do get some pretty great benefits. It can help maintain weight, aid in weight loss, bolster cardiovascular health and play a role in maintaining healthful blood lipid levels. It can also help with sleep and boost mood.
Get your husband on board and maybe instead of a nightly cocktail, the two of you can head outside after dinner for a companionable (and brisk) walk.
Eve Glazier, M.D., MBA, is an internist and assistant professor of medicine at UCLA Health. Elizabeth Ko, M.D., is an internist and primary care physician at UCLA Health. Send your questions to firstname.lastname@example.org, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.