The Cancer Research
Headlines based on individual studies swing from portraying coffee as a source of protective antioxidants to suggestions that coffee poses a cancer risk. However, research shows that drinking coffee reduces the risk of endometrial and liver cancer.
In decaf coffee, although caffeine is lower and phenolic acid content may be slightly lower, too, protective phytochemicals still add up. Most human studies show a similar reduction in cancer risk when looking at regular and decaf coffee.
When you hear concerns about a compound called acrylamide in roasted coffee beans, it’s important to understand that no links have been established between acrylamide in food and cancer risk for humans. Acrylamide increases cancer risk for lab animals at vastly higher amounts than what people get from coffee.
Interpreting the data
After a systematic review of the global scientific literature, AICR/WCRF analyzed how coffee and its nutrients affect the risk of developing cancer.
- Evidence categorized as “convincing” or “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 convincing or probable judgment is strong enough to justify recommendations.
- There is probable evidence that coffee DECREASES the risk of:
- Endometrial and liver cancers
- Evidence categorized as “limited suggestive” means results are generally consistent in overall conclusions, but it’s rarely strong enough to justify recommendations to reduce the risk of cancer.
- There is limited evidence that coffee may DECREASE the risk of:
- Mouth, pharynx, larynx and skin cancers, though more research is needed to determine if these are cause and effect associations.
Ongoing Areas of Investigation
Cell and animal studies show the effects of several phytochemicals in coffee that could help control cell growth and reduce cancer cell development.
- In cell and animal studies, phenolic acids increase cells’ antioxidant and anti-inflammatory defenses against damage that could lead to cancer. Emerging evidence in animal studies suggests they may also slow carbohydrate absorption from the digestive tract and decrease insulin resistance, and also support health-promoting microbes of the gut microbiota, creating an environment in the body less likely to support cancer.
- Lignans increase antioxidant, anti-inflammatory and carcinogen-deactivating enzymes in cell studies. In the lab, lignans can shift growth factors and estrogen metabolism to reduce cancer cell growth and development and to promote self-destruction of abnormal cells.
- Caffeine speeds the passage of any carcinogens through the digestive tract, reducing the time the colon is exposed to these substances. Cell studies show caffeine influences cell signaling to decrease colorectal cancer development.
- Melanoidins form during the roasting process and may act locally in the gut, supporting a healthy gut microbiota or increasing colon motility.
- In cell and animal studies, the diterpenes kahweol and cafestol stimulate enzymes that deactivate carcinogens, block enzymes that activate them and support the body’s antioxidant defense system. In cell studies, they decrease the growth of cancer cells and increase their self-destruction.
Most human studies related to coffee and cancer risk compare groups of people who consume different amounts of all types of coffee. Limited studies that analyze regular and decaf coffee separately generally find similar results.
Coffee reduces the risk of liver and endometrial cancers, with limited evidence indicating the potential to reduce risk of mouth, pharynx, larynx, and certain skin cancers. Analysis combining results of studies show no significant association of coffee consumption and other major cancers, including pancreatic, breast, ovarian, prostate, lung, esophageal, colorectal and others.The AICR/WCRF Third Expert Report categorizes evidence for these cancers as too limited to draw a conclusion.
Human intervention trials and observational population studies show several mechanisms that could explain how coffee consumption reduces cancer risk. However, the evidence is still emerging, and mechanisms may vary in relevance for different types of cancer. These include:
- Increased markers of antioxidant status and reduced markers of inflammation and DNA damage after several weeks in human trials, although results can be inconsistent.
- Improved insulin sensitivity and reduced circulating levels of insulin. Some evidence suggests this may especially occur in people with overweight. This could help reduce the risk of cancers in which excess levels of insulin promote growth.
- Higher levels of sex hormone-binding globulin (SHBG) to tie up estrogen, with reduced estrogen available to promote estrogen-sensitive cancers.
Tips for Selection, Storage and Preparation
Roasting time affects coffee beans’ color and flavor.
- Light: coffee will have a higher acidity, some tartness and more of the original bean’s flavor; less “roast” flavor.
- Medium: sweeter than light roast, but still contains some original bean flavor and aroma.
- French: beans are becoming a dark brown and appear oily. It is often used for making espresso.
- Dark (Italian or Dark French): predominant flavors come from roasting; it’s smoky and less acidic.
Choose the type of grind that’s right for your brewing method.
- Finely ground coffee is best used for espresso drinks. Espresso is brewed very quickly, so the smaller coffee particle size means more of its surface area is exposed to the hot water. This allows for more of the coffee bean contents to be extracted into the water.
- Medium grind works well for automatic drip coffee makers.
- Coarse grind is commonly used for French press pots.
- Store in an airtight container in a dark spot at room temperature. Air, moisture, heat and light all cause coffee to quickly lose its fresh flavor.
- For best flavor, use whole beans within two weeks and ground coffee within a few days.
- Although coffee experts advise against storing coffee in the refrigerator (the high moisture causes coffee’s flavor to deteriorate rapidly), you can wrap small amounts in airtight bags and freeze for up to a month.
- Coffee has a complex flavor; it contains hundreds of aroma compounds, some of which are described as nutty, flowery, chocolate-like and spicy. To extract a good balance of flavors and limit the bitter taste, the ideal brewing temperature is 190-200 degrees F for the water for any type of brew.
- American drip coffee is the lightest brew and Italian espresso the strongest. Typical proportions of coffee to water (in weight) are 1:15 for American; 1:5 for espresso.
- Coffee made with a French press, or press pot, retains more flavor, essential oils and the cafestol and kahweol compounds than drip methods.
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- World Cancer Research Fund/American Institute of Cancer Research. Continuous Update Project Expert Report 2018. Other dietary exposures and the risk of cancer. Available at dietandcancerreport.com.
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- National Cancer Institute. Acrylamide and Cancer Risk. https://www.cancer.gov/about-cancer/causes-prevention/risk/diet/acrylamide-fact-sheet. Accessed April 22, 2019.
- World Cancer Research Fund/American Institute of Cancer Research. Continuous Update Project Expert Report 2018. Non-alcoholic drinks and the risk of cancer. Available at dietandcancerreport.org.
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