Cancer myth: Coffee, tea, hot beverages and cancer
Origin of the myth
After water, tea and coffee are the most frequently consumed beverages in the world. Given their popularity, it is not surprising that people might wonder about their safety. Consequently, the relationship between tea and coffee and cancer risk has frequently been the subject of research studies.
Coffee is produced from ground, roasted coffee beans, which are the dried seeds of coffee plant berries. Instant coffee is made up of the soluble solids derived from dried, double-brewed coffee.
In 2007 the authoritative World Cancer Research Fund (WCRF) reviewed 66 studies and concluded that it is unlikely that coffee has any substantial effect on the risk of developing pancreatic cancer1. The WCRF also reviewed 24 studies investigating coffee and kidney cancer, and concluded that an association between coffee and risk of kidney cancer was unlikely.1
More recently, some studies have shown that coffee may protect against certain types of cancer, such as kidney, endometrial and possibly bowel cancers. However, a 2010 review of studies investigating the relationship between coffee drinking and risk of cancer of the pancreas, kidney, bowel, breast, endometrium, ovaries, liver, prostate and stomach found that across all sites, evidence largely points to a lack of an effect.2
Tea is made from the leaves of the Camellia sinensis plant. The difference between green and black tea comes from how they are processed after picking. Tea is a rich source of flavanoid antioxidants in the polyphenol category. Herb teas are technically not tea as most come from plants other than Camellia sinensis.
Broadly, more than 2,000 studies have found little or insufficient consistent evidence to suggest tea consumption increases risk of any of the above cancersThere is some evidence that mate, which is drunk almost exclusively in parts of South America, is linked to an increased risk of oesophageal cancer; however the scaldingly hot temperature at which it is traditionally consumed is considered to be responsible for any increased cancer risk.1
Overall, drinking tea is more likely to be beneficial than harmful with regard to cancer risk, although the risk appears to be reduced only slightly.
Green tea and cancer
Most studies showing a benefit have been conducted in Asia where mostly green tea is consumed. Therefore green tea may be more effective than other types of tea in reducing the risk of some cancers. However, more studies into green tea are needed before any conclusions can be reached.
A Cochrane review of 51 studies with over 1.6 million participants found that overall, current evidence is conflicting and insufficient to make any firm recommendations regarding green tea consumption for cancer prevention.3
There is some evidence that cancer can be initiated by constant irritation of body surfaces (like skin and the lining of the mouth and throat). Extremely hot water can serve as this constant irritant.
Research has shown that the way in which mate, a herb based infusion drink consumed almost exclusively in South America, is drunk can increase the risk of oesophageal cancer (the oesophagus connects the mouth with the stomach).1 Mate is drunk with a metal straw which is left in the mouth like a tobacco pipe. This, combined with extremely hot water, results in a constant ‘assault’ to the lining of the throat.
There is very limited evidence of similar effects with tea and coffee drinkers based on the most common means of consumption.
Regular moderate consumption of tea and coffee is unlikely to affect your risk of cancer. It is, however, recommended that you avoid drinking scalding hot water-based beverages.
• Cancer Council Australia’s Position statement on tea and cancer: http://www.cancer.org.au/policy-and-advocacy/position-statements/nutrition-and-physical-activity/
1. World Cancer Research Fund and America Institute for Cancer Research. Food, nutrition, physical activity and the prevention of cancer: A global perspective. Washington DC: AICR; 2007.
2. Arab L. Epidemiologic evidence on coffee and cancer. Nutrition and Cancer. 2010;62:271-283.
3. Boehm K, Borrelli F, Ernst E, Habacher G, Hung S, Milazzo S, et al. Green tea (Camellia sinensis) for the prevention of cancer. Cochrane Database of Systematic Reviews. 2009. Issue 3. Art. No.: CD005004. DOI: 10.1002/14651858. CK005004.pub2.