The Cancer Research
Coffee contains a variety of phytochemicals, many of which have antioxidant properties. Coffee's possible link to cancer is a well studied one, with over 1,000 studies on the topic. Early in the research, some studies hinted that coffee might increase cancer risk. Larger and more well-designed studies now suggest the opposite: it may be protective for some cancers.
Current Evidence: AICR/WCRF Expert Report and Its Updates (CUP)
Coffee, brewed from the beans of a small shrub or tree, contains vitamin B2 (riboflavin) and a variety of phytochemicals. After a systematic review of the global scientific literature, AICR/WCRF weighed the strength of the evidence linking coffee to risk of cancer development. This comprehensive review concluded:
- There is strong – probable - evidence that coffee LOWERS risk of endometrial cancer
- There is strong – probable - evidence that coffee LOWERS risk of liver cancer
Evidence categorized as "probable" means there is strong research showing a causal relationship to cancer – either decreasing or increasing the risk. The research must include quality human studies that meet specific criteria and biological explanations for the findings. A probable judgement is strong enough to justify recommendations; recommendations have not been made about coffee as there are still too many unanswered questions.
- There is also limited evidence that coffee may decrease risk of mouth, pharynx, larynx and skin cancers, though more research is needed to determine if these are cause and effect associations.
Source: AICR/WCRF. Diet, Nutrition, Physical Activity and Cancer: A Global Perspective, 2018.
”There is a tremendous amount of evidence out there on coffee and cancer risk and now the research is consistent and clear... showing coffee is not a risk for most of the cancers studied.”
- Lenore Arab, PhD, epidemiologist
University of California, Los Angeles
Open Areas of Investigation: Laboratory Research
Laboratory studies are focusing on coffee beans' lignans and phytochemicals. In cell and animal studies, scientists have identified several phytochemicals that help control cell growth and reduce cancer cell development.
- For colorectal cancer, one explanation of why coffee may show protection is its caffeine content. Caffeine may speed carcinogens' passage through the digestive tract, reducing the time our body is exposed to these substances. Cell studies show caffeine influences cell signaling to decrease colorectal cancer development.
- Chlorogenic acid shows antioxidant activity in lab studies. Caffeic acid seems to serve as an antioxidant and act in several stages of cancer development, helping regulate cell growth, reduce inflammation and increase self-destruction of cancer cells.
- In cell and animal studies, kahweol and cafestol stimulate enzymes that render carcinogens harmless and block the proteins that activate carcinogens.
- Coffee is also a source of lignans, compounds that cell culture and animal studies suggest may shift estrogen metabolism, growth factors and regulators of cell growth to reduce cancer cell growth and development and to promote self-destruction of abnormal cells.
Open Areas of Investigation: Human Studies
Population studies typically look at total coffee consumption. Studies that analyzed regular and decaf coffee separately generally find similar results.
Relatively large and well-controlled population studies now provide good evidence that up to six cups of coffee per day do not increase the risk of most cancers. Current research even suggests that coffee might decrease risk of certain cancers. In some population studies, people who drink moderate amounts of coffee daily show modestly reduced risk of a wide range of cancers, especially endometrial and liver cancers, although studies show wide individual variation in impact. A 2012 large U.S. population study linked daily coffee consumption with lower overall mortality during the course of the study. When looking at cause-specific deaths, moderate consumption was not linked to cancer-related deaths.
There are several hypotheses on how coffee may possibly decrease cancer risk. Coffee is a major source of antioxidants. Limited small intervention studies suggest that coffee may improve markers of antioxidant status and reduce markers of inflammation in the short-term. Animal studies and human studies both suggest that regular and decaffeinated coffee may decrease insulin resistance, a condition that leads to high insulin levels in the body. Reducing insulin resistance could help reduce risk of cancers whose growth is promoted by excess insulin.