Many people assume that a shot of soju or a can of beer poses little threat to their health. But a new study has found that people with diabetes or prediabetes face a higher risk of colorectal cancer even when they drink relatively little.
A joint research team from Samsung Medical Center and Soongsil University analyzed 4,475,492 adults who underwent national health screenings in 2012, examining how blood sugar levels and alcohol consumption affect the risk of developing colorectal cancer, according to the latest issue of the Journal of the National Cancer Institute (JNCI). The median follow-up period was 9.3 years, during which 51,592 participants were diagnosed with colorectal cancer.
Blood sugar status alone made a difference in cancer risk. Fasting blood glucose below 100 mg/dL was classified as normal, while readings between 100 and 125 mg/dL were categorized as impaired fasting glucose. Diabetes was defined as fasting blood glucose of 126 mg/dL or higher, or having received a prescription for diabetes medication at least once a year under a diabetes diagnosis code.
Compared with people with normal blood sugar, the risk of developing colorectal cancer was 11% higher in those with impaired fasting glucose and 26% higher in diabetes patients. Adding alcohol widened the gap further. The researchers classified daily consumption of less than 30 grams of alcohol for men and less than 20 grams for women as moderate or lower drinking. In practical terms, 20 grams of alcohol equals about two to three shots of soju, and 30 grams roughly three to four shots.
Alcohol Is Poison for Those With High Blood Sugar
Among moderate drinkers, people with impaired fasting glucose faced a 23% higher risk of colorectal cancer than non-drinkers with normal blood sugar, the analysis found. For diabetes patients, that risk rose to 48%. The findings suggest that alcohol can act as a factor that further amplifies colorectal cancer risk in people with elevated blood sugar.
The gap grew wider among heavy drinkers. Compared with non-drinkers with normal blood sugar, colorectal cancer risk was 17% higher among heavy drinkers with normal blood sugar, 41% higher among heavy drinkers with impaired fasting glucose and 77% higher among heavy drinkers with diabetes.
Notably, the study also observed a synergistic effect: when people with impaired fasting glucose or diabetes drank alcohol, their colorectal cancer risk exceeded the simple sum of the two risk factors taken separately. According to the research team, drinking alcohol can lead to the accumulation of acetaldehyde, a carcinogen produced during alcohol metabolism, and can increase mucosal inflammation and oxidative stress. High blood sugar can likewise raise oxidative stress by generating advanced glycation end products and activating inflammatory signaling pathways. The team said the overlap of these two processes may create an environment in which colon cells are vulnerable to turning cancerous.
The researchers also suggested that a mutation in the ALDH2 gene, which impairs the breakdown of acetaldehyde and is relatively common among East Asians including Koreans, may be one reason that even modest drinking raises colorectal cancer risk.
The research team said the study confirmed an association between moderate or lower drinking and increased colorectal cancer risk, and that the link was especially pronounced in people with impaired fasting glucose or diabetes. The more abnormal a person's glucose metabolism, the more minimizing alcohol intake can help lower colorectal cancer risk, the team said.
Colorectal cancer is the third most common cancer in South Korea. According to national cancer registry statistics released by the Korea Central Cancer Registry in 2026, colorectal cancer accounted for 32,610 of the new cancer cases diagnosed in the country in 2023, or 11.3% of all cancers, making it the third most frequent. Survival rates exceed 95% when the disease is caught early, but cumbersome screening procedures mean many cases are detected late.
