Averaging more than 14 alcoholic drinks per week over a lifetime — that’s two or more drinks per day — can significantly raise your chances of developing colorectal cancer, particularly rectal cancer, according to a large new study.
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Results published this week in the journal Cancer showed that lifetime heavy drinkers had a 25 percent higher risk of developing colorectal cancer and a 95 percent higher risk of developing rectal cancer than lifetime light drinkers.
It’s possible, though, for that risk to be reversed. Heavy drinkers who quit completely or substantially cut back saw their odds of developing colorectal cancer drop.
“There was no difference in colorectal cancer risk between light drinkers and former drinkers,” says the co–senior study author Erikka Lotfield, PhD, MPH, a researcher with the National Cancer Institute.
Alcohol Damage Builds Over a Lifetime
The findings were based on data from just over 88,000 adults who were enrolled in the National Cancer Institute’s Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial.
The study separated participants into three groups:
- Light Drinkers Less than 7 drinks per week for women, or less than 14 per week for men
- Moderate Drinkers Between 7 and 14 drinks per week for women, or 14 and 21 drinks for men
- Heavy Drinkers More than 14 drinks per week for women, or more than 21 drinks for men
Over 20 years of follow-up, almost 1,700 participants developed colorectal cancer, with people who drank heavily throughout that time period disproportionately represented.
“What this study really underscores is that alcohol risk builds over time,” says Cedrek McFadden, MD, a colorectal surgeon with Prisma Health in Greenville, South Carolina, and a medical adviser to the Colorectal Cancer Alliance.
“It is not just about what someone drank last year or last weekend,” adds Dr. McFadden, who was not involved in the study. “Looking at lifetime drinking patterns gives us a clearer picture of how long-term exposure relates to colorectal cancer, and the association was especially noticeable for rectal cancer. From a clinical standpoint, that reinforces alcohol as a meaningful and preventable cancer risk factor rather than a theoretical one.”
Clear Benefits From Cutting Back on Alcohol
Study participants reported their drinking habits on four separate occasions during the 20 years of follow-up. This allowed researchers to further separate participants into never drinkers, former drinkers, and current drinkers, and analyze how changes in drinking over time may impact cancer risk.
They found that former heavy drinkers could lower their odds to the same level as current light drinkers by quitting or seriously cutting back on alcohol.
“What’s especially important is that the study suggests that quitting alcohol may lower risk, which gives people something positive and actionable to work toward,” says Marianne Cusick, MD, a colon and rectal surgeon with UT Health Houston, who wasn’t involved in the study.
The study also found that compared with current light drinkers, former drinkers had 42 percent lower chances of developing noncancerous colorectal tumors, which can go on to become cancerous. Data regarding this, however, was limited, according to the authors.
Why Might Alcohol Elevate Cancer Risk?
The analysis is the latest in a long line of research indicating that alcohol may cause cancer, including colorectal, breast, liver, and esophageal.
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The National Cancer Institute theorizes that alcohol may heighten cancer risk because the body breaks down ethanol in alcoholic drinks into acetaldehyde, which is a toxic chemical and a probable human carcinogen. Acetaldehyde can damage both DNA and proteins.
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“In simple terms, alcohol is broken down into chemicals that damage healthy cells,” says Richard Wender, MD, a professor and the chair of family medicine and community health at the University of Pennsylvania in Philadelphia, and a medical adviser to the Colorectal Cancer Alliance. “Damage to healthy cells increases cancer risk.”
The National Cancer Institute adds that alcohol may impair the body’s ability to absorb a variety of nutrients that may ward off cancer, including:
- Vitamin A
- Nutrients in the vitamin B complex, such as folate
- Vitamin C
- Vitamin D
- Vitamin E
- Carotenoids
Recognizing Strengths and Limitations
Although the large sample size and 20-year follow-up make these research results meaningful, the study was observational, so it shows associations rather than direct cause and effect. In other words, it shows a link between heavy drinking and increased colorectal cancer risk rather than proving that heavy drinking can cause colorectal cancer.
Additionally, people in the study self-reported their alcohol intake, and they may have underestimated their true consumption, Dr. McFadden says.
Dr. Cusick further notes that the research did not factor in the effects of lifestyle factors like diet and exercise, or the impact of other medical conditions.
The study also did not examine differences between males and females, and among different ethnic and racial groups.
Screening for Colorectal Cancer Is Vital
Colorectal cancer is the second leading cause of cancer death after lung cancer.
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Early detection improves chances for survival, so it’s important to recognize the signs. Symptoms of colon and rectal cancer can include:
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- A change in bowel habits, such as more frequent diarrhea or constipation
- Rectal bleeding or blood in the stool
- Ongoing discomfort in the belly area, such as cramps, gas or pain
- A feeling that the bowel doesn’t empty all the way during a bowel movement
- Losing weight without trying
The symptom that sets rectal cancer apart from colon cancer is a persistent change in bathroom habits: constipation, bloating, or diarrhea that just won’t let up.
“Most people have no symptoms early on, which is why screening is so important,” says Cusick.
The United States Preventive Services Task Force says that all adults at average risk of colon and rectal cancer should begin screening at age 45.
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Are Other Factors Contributing to Increasing Colorectal Cancer Rates?
Colorectal cancer rates overall have been decreasing in the United States, driven mostly by fewer cases in adults 65 and older, who are most affected by it. But rates have been increasing at a worrying pace among adults younger than 50.
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At the same time, though, young adults are drinking less alcohol than in the past.
“The risk of colorectal cancer is increasing in this population, and we are not sure why,” says Dr. Wender, who was not involved in the study. “It may be due to higher alcohol intake in the past — but alcohol is not the only issue.”
While recognizing that alcohol can be unhealthy, he and other medical experts want to see more research focusing on what might be driving the surge in colorectal cancer.
For McFadden, the message of this study is clear: “If you drink, less is better, especially over the long term. Most importantly, staying up-to-date with colorectal cancer screening remains the most effective way we have to prevent cancer and detect problems early.”
