Dry January has come to an end — at least for those who jumped on the trendy post-holiday no-booze wagon.
The benefits of drinking less alcohol are well documented. A systematic review of 63 studies, for example, found that reducing or giving up alcohol reduced people’s risk for hospitalization, injuries, and death. The lifestyle change also improved people’s physical and mental health as well as their quality of life.
When it comes to cancer risk, however, the benefits of quitting or cutting back on alcohol remain much less clear, according to a new report from the cancer agency of the World Health Organization (WHO).
After reviewing dozens of studies, the International Agency for Research on Cancer (IARC) concluded that, for most alcohol-related cancers, there is limited evidence to support a link between eliminating or reducing alcohol consumption and lowering of cancer risk.
More specifically, the IARC Working Group, which included 15 scientists from eight countries, reported “limited” evidence on this association for laryngeal, colorectal (CRC), and breast cancer as well as «inadequate» evidence for pharyngeal and liver cancer.
The report did highlight two exceptions: Reducing or quitting alcohol was associated with a lower risk for both oral and esophageal cancer. The IARC working group based this conclusion on large studies of long-term alcohol cessation in these cancer types.
Still, the authors noted, “significant scientific gaps” exist for most alcohol-related cancers.
Take the data on CRC. Two studies found that reducing alcohol consumption did appear to lower CRC risk, while two others — which focused on the duration of quitting — did not suggest a reduced risk for CRC.
“Given the inconsistencies among studies and the few studies on duration of cessation, the Working Group concluded that there was limited evidence that alcohol reduction or cessation reduces colorectal cancer risk,” the authors wrote.
For liver cancer, the experts did note an association between quitting alcohol and lower cancer risk, but that cohort study only included individuals with alcohol-related liver disease. Outside of this study, the IARC group found no clear association between quitting drinking and liver cancer among people without alcohol-related liver disease in the other 11 studies evaluated.
For pharyngeal cancer, the evidence was limited overall, but one analysis looking at long-term cessation and oropharyngeal or hypopharyngeal cancer found a 26% lower risk (95% CI, 0.50-1.09). That association went away, however, after adjusting for detailed smoking history (odds ratio, 0.95; 95% CI, 0.56-1.61), and the working group concluded, overall, that «there was inadequate evidence that alcohol reduction or cessation reduces pharyngeal cancer risk.”
The IARC working group did find sufficient evidence linking drinking cessation and reduced risk for oral and esophageal cancers.
For instance, an international pooled analysis, which included 12 studies assessing a link between quitting smoking and alcohol and oral cancer risk, found that longer duration since quitting was associated with lower risk. Not drinking for up to 4 years was associated with a 19% lower risk for oral cancer, quitting for 5-9 years was associated with a 23% lower risk, while quitting for 20 years was associated with 55% lower risk.
“Given the consistent evidence of a reduced risk of oral cancer associated with long-term alcohol cessation,” the IARC working group concluded that there was “sufficient evidence that alcohol reduction or cessation reduces oral cancer risk.”
The working group also found “sufficient evidence from mechanistic studies that alcohol cessation reduces alcohol-related carcinogenesis.” In other words, quitting drinking appeared to reverse certain cancer-promoting biological mechanisms.
Outside the recent IARC report, some individual studies have suggested that quitting or cutting back on alcohol can reduce the risk for certain cancers.
For example, a large population-based study of about 4.5 million individuals in Korea found a lower risk for alcohol-related cancers among mild drinkers who quit (adjusted hazard ratio [aHR], 0.96) and heavy drinkers who reduced their drinking levels to mild (aHR, 0.92) or moderate (aHR, 0.91). These findings, however, may not be generalizable beyond East Asian populations.
Addressing the existing evidence gaps could help “support alcohol-control measures to reduce consumption,” the IARC working group concluded.