Explained | How much alcohol does it take to raise your cancer risk?

The surgeon general of the US Public Health Service warned Friday that even light or moderate alcohol consumption can increase a person’s risk of cancer.

In a new report, Dr Vivek Murthy, the surgeon general, said alcohol use had been directly linked with at least seven types of cancers, including those of the mouth, throat, larynx, esophagus, breast, liver, and colon and rectum. Globally, 741,300 cancer cases were attributable to alcohol consumption in 2020.

But public awareness of the link is low: Only 45 per cent of Americans believe alcohol has a significant effect on whether someone develops cancer, according to a 2019 national survey by the American Institute for Cancer Research.

Research has shown that the more alcohol a person drinks — particularly the more a person consumes regularly, over time — the greater the risk of cancer. The association is true for all types of alcohol: beer, wine and spirits.

But even what we think of as “light” or “moderate” drinking — up to one drink per day — increases the risk of some cancers, like those of the mouth, pharynx and breast.

“There is no safe level of alcohol when it comes to cancer risk,” said Dr. Ernest Hawk, vice president and head of the division of Cancer Prevention and Population Sciences at the University of Texas MD Anderson Cancer Center.

The amount you drink affects your risk.

The surgeon general’s report defines a standard drink as containing 14 grams of alcohol — about the amount in a 5-ounce glass of wine, a 12-ounce beer, or a 1.5-ounce shot of liquor. The report looked at evidence on cancer based on how much people consume every day or week.

Less than one drink per week: Research on the relation of very light drinking to cancer is limited. Murthy’s report looked at what’s known as the absolute risk — or the chance of a certain outcome happening in a given time period — of specific cancers at various levels of drinking. To do that, it looked at data from an Australian study of nearly a quarter-million adults published in 2020.

On average, the report found, about 17 in 100 women who consumed one drink a week or less would develop alcohol-related cancers over the course of their lives. About 11 in 100 women would develop breast cancer, which is considered an alcohol-related cancer. Research suggests alcohol can increase estrogen, a sex hormone linked to breast cancer.

Men who consumed less than one drink per week had about a 10% chance of developing any alcohol-related cancer over their life span.

Researchers considered this “less than one drink per week” group the reference group, against which they compared higher levels of drinking. Like many studies, they did not include non-drinkers to avoid what is known as the “sick quitter” effect — which happens when a study’s data is muddled by those who stopped drinking because of an illness.

One drink each day:

For years, it was widely thought that low or moderate amounts of alcohol were good for you, particularly for your heart. But in recent years more research has shown that even one drink a day is linked to greater health risks.

The surgeon general’s report said the lifetime risk of developing any alcohol-related cancer jumped to 19% (19 of 100 women) among those who consumed one alcoholic drink each day (seven drinks a week). At this level, the lifetime risk of breast cancer increased to 13.1%, or 13 of 100 women.

Murthy’s report said that among men who had one drink per day, about 11 of 100 on average would develop an alcohol-related cancer during their lifetime.

Though the absolute increases in risk may sound small, they reflect a notably increased relative risk compared to people who drink less alcohol.

A 2013 study in the Annals of Oncology that specifically looked at the association between “light drinking” and cancer found that compared with people who did not drink, those who drank up to one alcoholic beverage a day had a 30% higher chance of developing esophageal cancer, a 17% higher chance of developing cancer of the oral cavity and pharynx and a 5% higher chance of developing breast cancer.

Two drinks per day: At two drinks each day (14 per week), the share of women who would develop alcohol-related cancers over their life span increased from 16.5 per cent (among the “less than one drink per week” group) to nearly 22 per cent, according to the surgeon general’s report. The share of those who would develop breast cancer increased to 15.3 per cent.

Among men drinking at that level, the share who would develop alcohol-related cancer over a lifetime increased to 13 per cent.

Four or more drinks a day:

In addition to being associated with cancers of the mouth, oropharynx, larynx, esophagus, breast and colorectal area, heavy drinking — generally defined as four or more drinks a day — is linked to cancers of the liver, stomach, gall bladder and pancreas.

A large meta-analysis comparing light, moderate and heavy drinkers with non-drinkers and occasional drinkers found that heavy drinkers had more than a twofold higher relative risk of liver and gallbladder cancer compared with non-drinkers and occasional drinkers. Their risk of stomach, lung and pancreatic cancer was about 15 per cent to 20 per cent percent higher.

Consuming four or more drinks in a two-hour sitting is considered binge drinking for women, while having five or more drinks qualifies as bingeing for men. While binge drinking has many known harms, most studies in humans haven’t looked at the differences in cancer risk between drinking a lot all at once or drinking the same amount stretched over several days, said Dr. Timothy Naimi, director of the Canadian Institute for Substance Use Research at the University of Victoria. “It’s an area of need in terms of future research.”

Your other risk factors matter, too.

While the report looks specifically at drinking levels, many other factors — including sex, genetics, diet and family history — also play a role in how alcohol consumption affects cancer risk.

For instance, it takes less alcohol to negatively affect women’s health than it does men’s, possibly because women take longer to metabolize alcohol and it remains in their system for longer periods of time.

Anyone with genetic mutations or family histories that predispose them to these types of cancers would be starting out at a higher baseline risk of cancer, experts said.

Certain behaviors and lifestyle choices could also exacerbate the risk of alcohol-related cancers. Drinking and smoking cigarettes, for instance, is known to compound the risk of head and neck cancers, said Elizabeth Platz, a cancer epidemiologist at Johns Hopkins Bloomberg School of Public Health. And drinking alcohol when you have poor diet and exercise habits can further raise the risk of becoming overweight or developing obesity, another disease associated with cancer.

Drinking less cuts (some of) the risk.

A working group of the International Agency for Research on Cancer recently found that long-term quitting or reducing alcohol consumption was linked to a reduced risk of oral and esophageal cancer. But it’s not clear whether or when cutting back brings the risk back down to baseline, the surgeon general’s report said.

Naimi said that even for people who drink more heavily, cutting back the amount of alcohol they consume somewhat will have health benefits in the long run. “Less is better,” he said.