The U.S. Surgeon General's recent recommendation to put cancer warnings on alcohol products marks a significant shift in how alcohol is viewed in terms of public health.
The recommendation is based on a growing body of research linking alcohol consumption to various forms of cancer. It also reflects alarming findings: alcohol is responsible for 20,000 cancer deaths and 100,000 cancer cases in the U.S. each year, according to the Surgeon General.
Dr. Robert Hiatt, an epidemiologist and professor emeritus at UCSF, said the evidence connecting alcohol to cancer has been accumulating over decades.
"The concern is that alcohol does seem to be associated with and causal for a number of different cancers -- seven to be exact," Dr. Hiatt told KCBS Radio's Bret Burkhart on this week's episode of "As Prescribed."
"Cancers of the mouth and throat and esophagus, which might seem logical because of the contact of the alcohol with those tissues, but also with breast and with liver and with colorectal cancer. So the alcohol doesn't come in direct contact with those tissues, but it reveals that the metabolism of alcohol generates a carcinogen, which gets around to other parts of the body," he added.
The way in which alcohol contributes to cancer risk is complex but well understood. The most studied and prominent connection is with breast cancer.
"After the initial studies that were done in the mid 80s, where we found an association with breast cancer, there were other studies that were done in other parts of the country and other parts of the world, which confirmed it," said Dr. Hiatt. "And then the questions became expanded to other sites. And so we looked at prostate cancer and colorectal cancer and other common cancers and found also relationships, not as strong, perhaps, but nevertheless, presence."
"So it has taken some time to get to the point where authorities like the Surgeon General or the National Academies feel like an effort to inform the public of the concerns is needed," he added.
Dr. Hiatt explained that alcohol can affect our bodies and increase cancer risk in three key ways.
"First of all, alcohol itself, the chemical ethanol, is not carcinogenic. But when it is consumed, it's metabolized into something called acetaldehyde. And acetaldehyde is carcinogenic," he said. "So this substance will cause DNA damage."
The second way is through oxidative stress. Alcohol promotes oxidation, a process that can damage DNA and other cell structures.
"The third way is just plain contact with tissues where other carcinogens will come into play. One of the most well-established relationships is among people who are smokers and drinkers with throat cancer or mouth cancer," Dr. Hiatt explained. "So there, we believe that what the alcohol is doing is allowing the carcinogens in the tobacco to get into the system and cause DNA damage."
For decades, studies suggested that moderate alcohol consumption might have benefits for heart health, particularly in reducing the risk of heart attacks and strokes. This has led many people to believe that moderate drinking might actually be good for you. However, as Dr. Hiatt pointed out, the latest findings have shifted the conversation.
"It has come to the point where the data and the evidence is much stronger for harm with alcohol at higher doses. So it is, sort of, a dose response -- it increases with a higher dose of alcohol. But nevertheless, we find relationships even at lower levels of alcohol consumption," he said.
Moderate drinking is defined as up to two drinks per day for men and one drink per day for women. While this level of drinking may seem relatively safe to many, Dr. Hiatt said there is no "safe" threshold for alcohol consumption when it comes to cancer risk.
"This isn't something where there's a threshold, where at some point, there's no risk. It's a continuous relationship so that even at very low doses, you can find some evidence of harm," he said. "So I think the way people should think about it is that moderate drinking... is still a risk, but a small risk."
Listen to this week's "As Prescribed" to learn more. You can also listen to last week's episode for tips on how to protect yourself as norovirus surges around the country, here.
“As Prescribed” is sponsored by UCSF.