Limiting or giving up alcohol completely can reduce the risk of developing oral cavity and oesophagus cancers, according to a special report from the International Agency for Research on Cancer.
However, the researchers said 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 giving up drinking will lessen the risk of these cancers, Farhad Islami, a cancer epidemiologist at the American Cancer Society and an author of the report, told STAT News.
“Given that many of these cancers have similar mechanistic pathways, we think we will see a similar association with reduction or cessation. That’s why we recommend more studies, so we can have stronger evidence.”
Previous research has strongly established that consuming alcohol raises the risk of several cancers, including breast, colorectal, liver, oral and oesophageal, Islami said.
“That’s already established. But we wanted to know, what if people stop drinking?”
That was the central question of the report, highlights of which were published in the New England Journal of Medicine.
A team of researchers with the IARC analysed dozens of previous studies to assess the strength of the evidence that cancer risk declines after reducing or ceasing alcohol intake.
These included both cohort studies, which follow participants over the years, and case-controlled studies, to try to analyse 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 drinking would reduce the risk of oral cavity and oesophagus cancer.
For oral cancer, quitting alcohol for five to nine 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 oesophageal cancer, not drinking 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.
How does alcohol cause cancer?
Islami said that alcohol metabolises to a compound called acetaldehyde – 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.
“This potent genotoxic compound can affect DNA, and may cause cancer.”
Smoking affects the microbiome, which can increase the levels of acetaldehyde produced in the mouth. So, smoking is synergistic in that way, he added.
“There are other factors as well. It can increase inflammation, cause oxidative stress, and 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.
“Which is why it is likely that the less you drink, 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 quit alcohol – but the evidence is just limited at this time,” he said.
Alcohol flushing is from the reduced functioning of acetaldehyde hydrogenase, which metabolises it to less dangerous compounds, and people who turn red while drinking 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.”
It’s well known that if someone stops smoking now, after one decade, their risk of cardiovascular disease drops by 60%. Risk of cancer and related diseases go down, compared to current smokers, by 50%.
“We want to look at this kind of information 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 hepatitis 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.”
Islami said that to understand this link better, the best evidence would be cohort studies.
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 for, or whether they 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.”
The American Cancer Society started a new one a few years ago called CPS3, but more are needed, he said.
Why so little evidence?
“The association with smoking and cancer has been known since the 1950s – and in 1964, the US Surgeon-General had a specific report on the link, heightening awareness and triggering campaigns.
“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. 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.”
Cohort studies take decades – from the time of recruitment to when the data are analysed and then published.
“There was also this idea that small amounts of alcohol might improve 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.”
Islami said it was important to emphasise that you don’t need to be a heavy drinker to increase your cancer risk. Even moderate, light drinking increases the chances.
See more from MedicalBrief archives:
Political action key to addressing alcohol-linked cancer
UK-China genetic study confirms that alcohol is a direct cause of cancer
Alcohol consumption linked to 4% of global cancer cases – WHO study