Researchers analyzed health data from US adults who participated in the National Cancer Institute (NCI) Prostate, Long, Colorectal, and Ovarian (PLCO) Cancer Screening Trial and were cancer-free when the study began. During 20 years of follow-up, colorectal cancer was diagnosed in 1,679 of the 88,092 participants.

Heavy Lifetime Drinking Raises Cancer Risk

Among current drinkers, those with an average lifetime intake of ≥14 drinks per week were classified as heavy drinkers. Compared with people who averaged <1 drink per week over their lifetime, heavy drinkers had a 25% higher risk of colorectal cancer. Their risk of rectal cancer was even greater, nearly doubling with a 95% increase.

When researchers examined drinking habits across adulthood, they found that people who drank heavily for many years had a 91% higher risk of colorectal cancer than those who consistently drank small amounts. Former drinkers, however, did not show an increased risk of colorectal cancer. They also had lower odds of developing noncancerous colorectal tumors, known as adenomas (which may go on to become cancerous), compared with current drinkers who averaged <1 drink per week. These results point to a possible benefit of alcohol cessation, although the researchers noted that data for former drinkers were limited.

Possible Biological Explanations

The link between alcohol use and increased cancer risk may be explained by harmful substances created when alcohol is broken down in the body or by alcohol's influence on gut microbes. Further research is needed to determine whether these biological processes directly contribute to cancer development.

"Our study is one of the first to explore how drinking alcohol over the life course relates to both colorectal adenoma and colorectal cancer risk. While the data on former drinkers were sparse, we were encouraged to see that their risk may return to that of the light drinkers," said co-senior author Erikka Loftfield, PhD, MPH, of the NCI, part of the National Institutes of Health.