A couple years ago, a researcher named Curtis Ellison took the podium in a crowded lecture hall at Boston University’s School of Public Health to tackle a question that had divided the university’s public health community: whether moderate drinking should be recommended as part of a healthy lifestyle. Ellison’s take? “I mean, it’s so obviously ‘yes,’” he told the crowd.

You’ve heard Ellison’s pitch before: A glass a day can make for a healthier heart and a longer life. On stage, he told the story of “Jackrabbit” Johannsen, a famed cross country skier who lived to be 111. Johannsen had four pieces of advice for a long and healthy life, Ellison said: “Don’t smoke, get lots of exercise, don’t drink too much.” He paused. “On the other hand, don’t drink too little, either.” The crowd erupted in laughter and applause.

But Ellison wasn’t going unchallenged. Watching from the other side of the stage was Tim Naimi, a public health professor at BU who studies binge drinking in the same building as Ellison. He was there to argue the less attractive position: Drinking is distinctly unhealthy. And not in the typical ways you might associate with alcoholism, but in the sense of increased cancer risk—even for moderate drinkers.

Alcohol’s potential health benefits may have been oversold by industry-funded research, distracting consumers from the realities of cancer risk.

For folks within the realm of public health, that’s no surprise. The World Health Organization has recognized alcoholic beverages as a Group 1 carcinogen since 2012, meaning evidence supports a link between alcohol and increased cancer risk. This past March, Jennie Connor, a preventative and social medicine researcher from New Zealand’s University of Otago, published a review of studies looking at the correlation between drinking and cancer, concluding that “there is strong evidence that alcohol causes cancer at seven sites in the body and probably others.” Her analysis credits alcohol with nearly 6 percent of all cancer deaths worldwide.

Connor’s use of the word “cause” separates her from most alcohol researchers and cancer advocacy groups in the US, where the conversation revolves around a more delicate term: “risk.” American consumers and researchers are both uncomfortable—or at least unfamiliar—with the idea of alcohol as health threat. When the American Institute for Cancer Research put out a survey to measure public perception of various cancer threats, less than half of respondents believed that alcohol was a risk factor for cancer. Which is odd, because 56 percent thought GMOs were, even though there’s no scientific proof that they are.

To be fair, the science around how alcohol impacts the body is still nascent. Ellison and Naimi’s debate wasn’t a mock trial: The public health community is split among people who think alcohol has its benefits and those who caution against its risks. The WHO’s designation puts alcohol in the same category as processed meats and sunlight: They’re carcinogenic, but that label doesn’t tell you how much is how carcinogenic. Consumers are faced with the conflicting message that moderate drinking can actually increase their level of good cholesterol and decrease their risk of heart disease, which kills more people in the US than anything else.

“Lots of us drink and we’d really like to believe drinking is good for us,” says Naimi. “But the research around that has really fallen apart in the last couple years.” Since Ellison made his confident statement into that mic two years ago, Naimi and many of his peers have gone on the offense against the studies that support alcohol’s potential health benefits, saying they may have been grossly oversold by industry-funded research—in the end, distracting consumers from the realities of cancer risk.

Bias in Booze Science

In late 1991, Ellison went on 60 Minutes to share the good news about red wine and heart health, and the idea took off. Underlying his claim were years of observational studies that compared moderate drinkers to non-drinkers. A handful of studies found that the moderate drinkers were actually healthier than the non-drinkers.

But in recent years, alcohol scholars like Connor and Naimi have criticized those studies for what’s become known as a “sick quitters” bias. Some of the groups of non-drinkers that were compared to moderate drinkers were actually groups of former alcoholics or people who were too sick to continue drinking, so they were generally sicker than the healthier moderate drinkers. When Naimi adjusted the results in a meta-analysis that took the bias into account, the study still showed that moderate drinkers were better off than non-drinkers when it came to heart health—but not by nearly as much as originally thought.

Ellison says recent studies have gotten more sophisticated about eliminating those selection problems. But that’s not the only source of bias in the literature. In the summer of 2014, the journal Addiction published a scathing editorial that outed Ellison for receiving “unrestricted educational donations from the (alcohol) industry.” That money had supported his work at BU, along with his leadership of a peer group that wrote positive reviews about studies highlighting the potential health benefits of drinking.

It wasn’t the first time the journal had called out the often-cozy relationship between alcohol academics and industry. Trade organizations like the Distilled Spirits Council, which represents alcohol companies and is the largest alcohol lobbying arm, often work hand in hand with regulators and researchers. Some researchers go on to work for their industry connections, like Samir Zakhari, a former director at the US National Institute of Alcohol Abuse and Alcoholism (the National Institutes of Health’s alcohol research division). After he retired from the NIH, he went to work for the Distilled Spirits Council.

The council, for its part, doesn’t buy the newer research that highlights the link between alcohol and cancer. Frank Coleman, a spokesman for the DSC, says that many of those meta-analyses are flawed, skewed by cherry-picking data points.

The Trouble with Analyzing Alcohol

Those biases are a direct challenge to the validity of science on alcohol and health. But even if they didn’t exist, the nature of drinking still makes it extraordinarily difficult to come up with reliable results. Health risks, including those for cancer, are based on a complex interplay of variables—lifestyle factors, age, genetic predispositions—and they play out differently in each individual’s body.

People who drink a bit of wine each day, for example, tend to sit down and drink it with meals. And they’re predominantly wealthier, more privileged consumers—making them predisposed to better health, says Ellison. Beer drinkers also tend to be more susceptible to binge drinking, he says.

Those factors can be difficult to separate from alcohol’s isolated effect on the body. “We’re not studying beer or wine specifically,” says Ellison. “We’re studying people who drink them.” Even low calorie beers come with a lot of empty calories, says Kenneth Portier, who directs the statistics and evaluation programs at the American Cancer Society. “Drink enough of it and it can put you in that other risk factor: obesity.”

Ellison doesn’t deny that there is a link between alcohol and cancer—he just thinks it’s only relevant for heavy drinkers. But that starts a whole new debate: What exactly constitutes moderate drinking, and how do you study moderate vs. heavy drinking in study participants with vastly different body sizes, metabolisms, and socioeconomic backgrounds? In order to guide people in making informed decisions, researchers will need resources from somewhere outside the alcohol industry to conduct randomized studies that can isolate alcohol’s impact on the body over the course of decades.

Still, the less-than-perfect current evidence suggests that about 15 percent of breast cancer deaths are alcohol-related, says Naimi. Nearly 20,000 cancer deaths are attributable to alcohol every year in the US alone, he says, and we’re not even the world’s biggest drinkers. Simultaneously, the craft beer market has grown into a $22.3 billion industry and AB InBev and SAB Miller, the world’s two largest alcohol companies, are in the midst of a mega merger. If there was ever a time to come to a consensus about what exactly alcohol does to our bodies, it would be now.

Shaping the Message

Connor’s analysis of existing alcohol research was a turning point for the conversation on booze and cancer. But once you’ve decided that alcohol is a substantial public health risk, you still need to convince drinkers of that fact. And it’s a lot easier to tell people drinking is good for them than to explain how and why it isn’t.

“Things that are familiar to us are perceived as less risky,” says Portier. “Most of us have been around alcohol our whole lives and we know people who drink and they’re not dead.”

It becomes even more difficult to construct a coherent public health message when consumers hear conflicting information. For each drink a woman has per day, her relative risk for breast cancer alone can increase by about 7 percent, says Susan Brown, who’s in charge of health education programs at Susan G Komen. But “people are often surprised and disappointed that there’s an association between alcohol and breast cancer,” she says. Many times, they've heard that moderate drinking is good for them. “That may be confusing or masking the message,” she says.

So right now, health groups like Susan G Komen and the American Cancer Society simply emphasize drinking in “moderation.” In public-health speak, that’s defined as one drink a day for women and two drinks a day for men (think of a drink more as a glass of wine or a bottle of fairly light beer, rather than a double martini).

But for most consumers, the concept of moderation is most closely tied to the phrase “drink responsibly,” an alcohol industry catch phrase that reminds customers not to drink too much—without actually defining how much is too much. “I worry sometimes that the breweries are trying to change the perception of risk to benefit their own equation,” says Portier.

That’s where policy comes into play. In the UK, for example, the Department of Health changed its alcohol guidelines from saying it was safe to drink moderately to acknowledging that “there are a number of serious diseases, including certain cancers, that can be caused even when drinking less than 14 units weekly.” While the risk for moderate drinking was low, they write, “there is no level of regular drinking that can be considered as completely safe.”

Look back at the public health messages around tobacco and you’ll notice they all share a common, simple message: stop smoking. There was no level of moderation that was considered risk-free, so there was no conversation around moderation. Alcohol, on the other hand, has a much more complex message: don’t drink too much, make sure you understand what “too much” means for you, and mitigate the risk of drinking by assessing any other risk factors you may have in your life. Not exactly great fodder for a catchy PSA. But in a world where drinking is so closely tied to culture, it may be the best option.

“It all comes down to perception of risk and how you want to live your life,” says Portier. Someone who is at a higher risk for heart disease than cancer, for example, may feel more inclined to have a glass of red wine each night than someone who has a strong family history of breast cancer. “People should make their own decisions about how much they drink,” says Naimi. “But I certainly think that people deserve to be more aware of this than they are now.”

To get there, Naimi goes back to the idea of conducting long term, comprehensive, randomized studies. That’s something both sides are anxious to see more of. Zakhari, the alcohol expert who works at the Distilled Spirits Council, says it’s crucial to look at alcohol consumption over a long period of time, since cancer usually develops very slowly. “These studies always ask women, ‘how much did you drink last week, last month, last year,’” he says. “But what they were doing last week or last month or last year has nothing to do with the initiation of cancer 20 years earlier. It’s like someone has food poisoning today and the doctor asks them what they ate for Christmas in 1980.”

Not that help isn’t on the way—sort of. According to the Wall Street Journal, AB InBev and Diageo (another heavyweight alcohol producer) are planning to work with a handful of other alcohol companies to pay for a randomized study that will look at the health implications of drinking. It’ll be run by the NIAAA, the same government division where Zakhari once worked.