Now that the vast majority of Americans don’t smoke, it’s hard to know what we’re supposed to do about the recent news that 40% of cancer cases are preventable. Drinking alcohol is one of the top risk factors — and yet doctors aren’t talking to patients about its connection to cancer.

Alcohol was third behind obesity and smoking among the “modifiable” risk factors according to this new study. You can’t walk into a doctor’s office without being put on a scale, and everyone knows smoking causes cancer, but drinking a glass of wine or two every night? Not long ago, that was considered healthy — due, researchers now say, to a systematic error in several widely publicized earlier studies.

And drinking is a bigger cancer risk factor for women than it is for men. About 300,000 women are diagnosed with breast cancer in the US each year. It’s by far the most common potentially lethal cancer among nonsmoking women.

Alcohol consumption accounts for about 16% of breast cancers, said the lead author of the study, Farhad Islami of the American Cancer Society. Most of the increased risk is attributable to people who exceed the current health guidelines of no more than one drink a day for women. But even a drink a day raises risk — especially if you’re filling up a big wine glass.

Drinkers of both sexes have an increased risk of liver cancer, esophageal cancer and other malignancies of the digestive tract, but these are not nearly as common as breast cancer.

There are still many critical questions that experts can’t answer until there’s more research: How much is a woman’s lifetime breast cancer risk elevated by heavy or binge drinking in college and early adulthood? How much can a woman reduce her risk by going from moderate drinking to abstaining? Are there women with certain risk factors that make them more prone to cancer induced by alcohol use? How and why does alcohol raise breast cancer risk?

There are a few studies suggesting that alcohol can cause breast cancer by increasing the amount of estrogen circulating in the bloodstream. Should women taking hormone replacement therapy skip the daily glass of wine? It might make sense, but it remains in the realm of things that need more study.

Instead, doctors usually recommend diligent annual screening mammograms if you want to try HRT, but of course, screening doesn’t prevent cancer. In the most optimistic estimates, programs of regular screening mammograms reduce cancer death by 20%, but more recent studies show less benefit along with a serious risk of unnecessary treatment.

In one of the many articles on the limitations of mammography, professor of medicine Russell Harris of the University of North Carolina suggests it’s more important for doctors to council women to stop smoking, maintain a healthy weight and cut back on drinking.

In June, the New York Times tried to quantify the risk of moderate drinking. One researcher said drinking seven drinks a week only costs you about two and a half months of life. The researcher, Tim Stockwell of the Canadian Institute for Substance Use Research, emphasized that was an average — most people may lose nothing, but a few will lose a lot.

It’s hard to isolate the effects of drinking because it’s tied up with other behaviors and conditions, he told me. Take the “sick quitter effect,” he said. People who get serious warnings from their doctors often quit drinking, and so studies can show a correlation between quitting drinking and getting sick — because getting sick caused people to quit. And some people don’t ever drink because they have health problems or are on medications. Missing that link is one reason earlier studies showed — wrongly — that moderate drinking was beneficial.

Some people who don’t drink any alcohol might compensate with other unhealthy behaviors. For example, consumption of sugary soda might explain a high incidence of heart disease and diabetes in Middle Eastern countries where many people never drink alcohol for religious reasons.

With alcohol, risk is associated with lifetime consumption, Stockwell said, and some studies show that a long-term pattern of youthful excess puts you at higher risk of heart disease when you’re older. We need more research to know how lifetime patterns of drinking affect cancer risk — all we know is that if you want to minimize your risk, it’s better not to drink.

But of course, minimizing risk isn’t everything. Drinking is an important part of celebrations and socializing, and we have to weigh those benefits against the health risks. Some people have a highly tuned palate and get enormous pleasure from fine wine, while some of us are just as happy with a fake beer as long as the company is genuine.

It’s also a major quality of life issue to be cancer-free, rather than facing surgery, radiation or chemotherapy. To estimate the trade-offs, we deserve better information — both from researchers and from our doctors.

F.D. Flam is a Bloomberg Opinion columnist covering science. She is host of the “Follow the Science” podcast.

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