Reducing or eliminating alcohol consumption reduces the risk of developing oral cavity and esophagus cancers, according to a special report from the International Agency for Research on Cancer. But more data are needed to conclude whether the same is true for several other cancer types, including colorectal, breast, and liver cancer.
Even so, it is likely that reducing or ceasing to drink alcohol will lessen the risk of these cancers, said Farhad Islami, a cancer epidemiologist at the American Cancer Society and an author of the report. “Given that many of these cancers have similar mechanistic pathways, we think we will see a similar association with reduction or cessation,” he said. “That’s why we recommend more studies, so we can have stronger evidence.”
Over the last couple of decades, studies have strongly established that consuming alcohol does raise the risk that people will develop several cancers, including breast, colorectal, liver, oral, esophageal, and more, Islami said. “That’s already established,” he said. “But we wanted to know, what if people stop drinking?”
That was the central question of the report, published online in the New England Journal of Medicine on Wednesday. A team of researchers with the IARC analyzed dozens of previous studies to assess how strong the evidence is that cancer risk declines after reducing or ceasing alcohol intake. These included both cohort studies, which follow a group of participants over the years, and case-controlled studies, which try to analyze the differences between people diagnosed with cancer and those who did not develop the disease.
The report found there was sufficient evidence that reducing or ceasing alcohol intake reduces risk for oral cavity and esophagus cancer. For oral cancer, ceasing alcohol consumption for five to 9 years was linked to a 34% relative risk reduction, and doing so for 10-19 years was linked to a 55% relative risk reduction. For esophageal cancer, ceasing alcohol for five-15 years had a 15% relative risk reduction, and for 15 years or more, was linked to a 65% relative risk reduction. Researchers found limited evidence that the same is true for larynx, colorectum, and breast cancer, and inadequate evidence for pharynx and liver cancer.
STAT spoke with Islami about the report, why there’s been insufficient work on the link between cancer and alcohol, and what we know so far on how alcohol causes cancer. This interview has been edited for length and clarity.
How does alcohol cause cancer? What’s the mechanism?
As soon as people drink alcohol, it metabolizes to a compound called acetaldehyde. This is from the microbes we have in the gastrointestinal tract, and it starts in the mouth. After a few minutes, the concentration of acetaldehyde goes up immediately in the saliva, gastric juices, colon, and in the blood. That’s a potent genotoxic compound. It can affect DNA, and it may cause cancer. Smoking affects the microbiome, and that can increase the levels of acetaldehyde produced in the mouth. So, smoking is synergistic in that way.
There are other factors as well. It can increase inflammation, cause oxidative stress, and alcohol can affect sex hormone levels. That can change the risk of breast cancer. Alcohol can also reduce absorption of some nutrients that are helpful to repair DNA damage — for example, folate.
This is why it’s very likely that the more you reduce alcohol, the greater the risk reduction of cancer. That’s what we expect, and we think it’s very likely the risk will also go down over time for all the other cancer types if you reduce or cease alcohol — but the evidence is just limited at this time.
I know that the reason behind alcohol flushing is that some people cannot metabolize acetaldehyde as easily. Does that mean people who turn red when drinking are at greater risk for cancer if they drink?
Yes, flushing is from the reduced functioning of acetaldehyde hydrogenase, which metabolizes it to less dangerous compounds. Those people are at even higher risk. But actually, for those with only one copy of the mutation it’s higher. Those who are homozygous or have two copies of the mutation are at lower risk. That’s because they become so affected or flushed by alcohol, that they don’t drink it.
What’s the utility behind understanding how cancer risk declines after alcohol cessation or reduction if we already know that alcohol consumption leads to cancer?
So, we know this for smoking already. We found if someone stops smoking now, after one decade their risk of cardiovascular disease goes down by 60%. Risk of cancer and related diseases go down, compared to current smokers, by 50%. We want to look at this kind of data for alcohol, but unfortunately there are not much data to say how long it takes to eliminate the risk from alcohol.
It’s important because there are some exposures where you may not see a lot of benefits after you reduce or eliminate the exposure. Some viral infections, like hep b or c, are like this. That’s why the hepatitis vaccine is recommended early in life. We also want to see this kind of evidence before recommending guidelines for people, and these kinds of studies help us to create risk predictions in the future. It can help policymakers increase awareness or find ways to reduce consumption of alcohol in the population.
What kind of evidence do we still need to get to understand this link better?
The best evidence we can get would be cohort studies, where we follow people over time. The issue with the evidence now is that many of the studies that were available just reported the risk for former drinkers without showing when they stopped drinking, how long they stopped drinking, or whether people continued drinking but reduced their consumption. We don’t have much data on that. It’d be great to have studies now that ask more questions about the duration of alcohol cessation or reduction.
There are some studies. The ACS [American Cancer Society] started a new one a few years ago called CPS3. But we still need more.
Why do you think we have so little evidence on this link currently?
The association with smoking and cancer has been known since the 1950s. Then in 1964, the surgeon general had a specific report on the association with smoking and cancer, which led to lots of campaigns and things.
The association with alcohol and cancer is more recent. A few surveys showed a large percentage of people didn’t know that alcohol consumption is associated with cancer risk, and surprisingly even many medical professionals did not. That may be a reason why we don’t have a lot of questions on alcohol consumption in earlier cohort studies.
These cohort studies take decades from the time you recruit people to when you can really analyze your data and publish. There was also this idea that small amounts of alcohol may improve your cardiovascular health. There’s still a belief there. Now, new evidence suggests that may not be. Other associations may have confounded those results, like many of the people who eat a Mediterranean diet also consume lots of fruits and vegetables. Also, the studies – they are sponsored by the alcohol industry.
It’s important to emphasize that a person doesn’t need to be a heavy drinker to increase risk of cancer. Even moderate, light drinking increases risk. The ACS recommends it’s best not to drink alcohol or, if you must, reduce it as much as you can.