Can alcohol cause cancer? Here's what the science says

A growing body of evidence has shown links between cancer and drinking alcohol.

In a warning Friday, U.S. Surgeon General Vivek Murthy said cancer risk increases with the number of drinks, but even one drink a day can be dangerous.

Current federal guidelines recommend that if people want to drink alcohol, women should drink no more than one drink per day and men no more than two.

"Alcohol is a well-established, preventable cause of cancer responsible for about 100,000 cases of cancer and 20,000 cancer deaths annually in the United States,” Murthy said in a statement announcing his advisory.

He added the death toll of alcohol-related cancer deaths was higher than the 13,500 deaths from drunken driving crashes annually in the U.S. But, he said, "the majority of Americans are unaware of this risk."

The science related to drinking has changed in recent years, leading to some confusion among consumers. At one point, moderate drinking was thought to be healthier than not drinking at all, because of possible benefits to the heart and bloodstream. A recent federal report supported that hypothesis, though the finding has been widely criticized. Other data finds that even moderate drinking, as Murthy said, can lead to health problems including cancer.

Numerous studies have linked alcohol consumption with cancers, including those of the mouth, esophagus, breast, liver and colon, said Timothy Rebbeck, professor of cancer prevention at the Dana-Farber Cancer Institute in Boston.

“More recent data have confirmed that even occasional alcohol consumption is associated with the risk of some cancers,” he said in a statement. Murthy’s warning appropriately emphasized the importance of limiting alcohol to reduce cancer risk, Rebbeck said.

The idea of a warning label was met with skepticism from trade groups representing alcoholic beverage manufacturers. The federal government should consider the entire body of scientific research – all harms and potential benefits – regarding alcohol before changing an existing warning label that does not mention cancer risks, Dr. Amanda Berger, senior vice president of science and research of the Distilled Spirits Council, said in a statement sent to USA TODAY.

While many lifestyle choices carry potential risks, she said the council doesn’t recommend anyone drink alcohol to gain any health benefits and urges adults who choose to drink alcohol to consult their doctor.

How does alcohol cause cancer?

The human body breaks alcohol down into chemicals that can damage DNA, causing cells to grow out of control and become cancerous, according to the National Cancer Institute.

Additionally, alcohol can block the body from breaking down certain nutrients that can increase cancer risk. Alcohol can also increase blood levels of the sex hormone estrogen, which has been linked to higher risk of breast cancer.

The combination of smoking and drinking is "multiplicative" ? even more harmful than adding the potential damage of either one alone, according to the cancer institute.

The extent to which drinking alcohol may lower cancer risk of some cancers isn't fully understood and may be indirect, the institute said.

What does research say?

A recent review of alcohol and cancer research by a National Academies of Science, Engineering and Medicine committee published in December is meant to shape U.S. Dietary Guidelines.

The review found people who drank moderately were less likely to die prematurely from any cause than those who never drank alcohol.

Moderate alcohol drinking was associated with higher risk of breast cancer, but the review couldn’t draw a conclusion on the association between moderate alcohol consumption and cancers of the mouth, throat, larynx and esophagus.

Others have disagreed with this assessment, including the National Cancer Institute, which warns that even those who drink no more than one drink per day and those who binge drink have "modestly increased risk" for some cancers.

The American Association of Cancer Research’s latest Cancer Progress Report highlighted the role alcohol has in causing cancer. Excessive levels of alcohol consumption increase risk for six cancers, from head and neck, to stomach cancers, the report said.

In the U.S., more than 5% of cancers were linked to alcohol consumption in 2019. Reducing consumption or stopping drinking altogether can decrease the risk of developing alcohol-related cancers by 8%, and for any cancer by 4%, the report said.

Drinks have varying levels of alcoholic content, noted Jiyoung Ahn, a cancer molecular epidemiologist at New York University Langone Health. A Scotch neat has an alcohol by volume (ABV) level upwards of 40%, while a Modelo, America's most popular beer has 4.4% ABV, and a White Claw hard seltzer, 5%.

It’s important to remember that any amount of alcohol in the body will break down into chemicals, such as acetaldehyde, that can cause cancer.

“If you drink more, it’s really clearly increasing your risk, so moderating and less drinking is better,” Ahn said.

Dr. Bruce Scott, president of the American Medical Association, a professional association of physicians, said Murthy's advisory will "make completely clear" the link between cancer risk and any alcohol consumption.

"(It) will bolster awareness, improve health, and save lives," Scott said in a statement. "Despite decades of compelling evidence of this connection, too many in the public remain unaware of alcohol’s risk."

Contributed: Adrianna Rodriguez and Claire Thornton

(This story has been updated to include new information.)

This article originally appeared on USA TODAY: Can alcohol cause cancer? Surgeon General's warning on risks