Question: I recently read that drinking coffee lowers the risk of bowel cancer coming back. Does that mean it reduces the risk of getting bowel cancer in the first place? How does coffee help the bowel?
Answer: Researchers have found intriguing links between coffee consumption and colorectal cancer risk. Regular coffee consumption is linked to a reduced risk of colorectal cancer occurrence and recurrence in some studies, including a recent large observational study in the Netherlands. But is there enough evidence to say that coffee could prevent colorectal cancer?
The Dutch study used data from a longitudinal study investigating nutritional and lifestyle factors linked to cancer recurrence among 1719 colorectal cancer patients. They found drinking four or more cups of coffee daily was associated with a 32% lower risk of colorectal cancer recurrence compared with drinking less than two cups daily. However, a U-shaped relationship existed between coffee consumption and all-cause mortality: optimal health was associated with drinking 3-5 cups a day. The lowest risk was at four cups. Mortality risk was higher as coffee consumption increased or decreased.
Still, this was just an observational study and correlation does not automatically imply causation. (Male pattern baldness, for instance, correlates with an increased risk of cardiac events, but no one would suggest men grow more hair to reduce their cardiovascular disease risk.)
So, is there a plausible explanation for how coffee might actively reduce the risk of colorectal cancer occurrence or recurrence, or is it simply a coincidence that moderate coffee drinkers have less colorectal cancer?
Linking coffee consumption to reduced cancer risk is not unusual, as coffee has anti-inflammatory and antioxidant effects and may contribute to the prevention of inflammatory and oxidative stress-related diseases, such as metabolic syndrome and type 2 diabetes. According to the World Cancer Research Fund, there is strong evidence that coffee intake reduces the risk of endometrial and liver cancers.
Coffee also has antiproliferative properties, inhibiting cell growth and spread, and pro-apoptotic properties, promoting cell death. Furthermore, coffee components that pass through our digestive system are processed by our gut microbiome, producing active metabolites that also have protective effects.
Japanese researchers recently analysed levels of 35 different dietary polyphenols in people’s blood and their colorectal cancer risk. Dietary polyphenols are found in most plant-based foods, including fruits, vegetables, cereals, pulses, tea and coffee. The researchers found stronger associations with polyphenols from coffee, such as dihydrocaffeic acid, ferulic acid and caffeic acid, with reduced colorectal cancer risk than with polyphenols from other foods. Caffeic acid from coffee, for example, has been shown to suppress colon cancer spread and have anti-inflammatory effects, and it may trigger apoptosis (spontaneous death) of colon cancer cells. Ferulic acid has been shown to suppress colon cancer cell growth, the researchers noted.
Still, we have much more to learn about coffee’s biological impacts before we can confidently say it may reduce colorectal cancer incidence or recurrence. So, for those who don’t drink coffee, there is no clear reason to start. And bear in mind that not all coffee is equal. Some coffee types, such as French press and Scandinavian brews, contain significant quantities of cafestol, which increases LDL cholesterol, thus negatively affecting cardiovascular health.
But if you enjoy coffee, then continuing to drink it at a moderate level (defined as 3-5 cups a day) is a good idea. Just time your coffee to enjoy it away from main meals to protect your iron intake, as coffee (and tea) can inhibit dietary iron absorption when consumed with or near meals. And bear in mind that caffeine, which can keep you awake: it has a half-life of 4-6 hours and can take 10-12 hours to leave your system. The American Academy of Sleep Medicine recommends you have your last cup no later than six hours before bedtime.
Colorectal health can also be improved by eating more fibre: most New Zealanders’ dietary fibre intake is notoriously low. Swapping refined carbs for wholegrains and eating more plant-derived foods such as fruits, vegetables, beans and legumes will boost your fibre intake. Eating dairy products, reducing red meat consumption, and avoiding processed meat and alcohol can also reduce the risk of colorectal cancer, says the World Cancer Research Fund.
