Frequently Asked Questions

Q1. A great deal is written about diet and all forms of cancer. What do expert bodies such as the International Agency for Cancer Research, say about coffee and cancer?

A. In 1991 the International Agency for Cancer Research (IARC), which is part of the World Health Organisation, classified coffee as being “possibly carcinogenic to bladder cancer” This classification was given because there was insufficient data available at the time to be more specific (2). However the report also stated that drinking coffee may even help to protect against some forms of cancer. This resulted in many further studies being undertaken.
The IARC Report included data on coffee and gastric cancer from five studies (2). There was no evidence of association in any and further studies confirm that coffee is unlikely to have any major effect on gastric cancer. Six studies providing data on cancers of the mouth, throat and oesophagus were considered in the IARC Report. There was no evidence of association with coffee consumption in any of them. (11, 23-26).
With relevance to breast cancer, again the IARC Report found no association with coffee consumption (2). This was more recently confirmed, in several studies including an Italian study involving nearly 6000 cases (27). Likewise, no consistent relation was observed between coffee with ovarian, laryngeal, lung, prostate, cervical, endometrial and thyroid cancers, Hodgkin's and non Hodgkin lymphomas, sarcoma, and skin melanoma (28, 29).

Q2. What is the latest thinking on coffee and bladder cancer?

A.Since the publication of the IARC Report in 1991, several studies have been undertaken on coffee and bladder cancer. The large amount of data resulting from a number of those studies on coffee and bladder cancer risk, clearly excludes, after making allowances for other possible causes, a strong association between coffee consumption and the risk of developing bladder cancer. In one recent study in the Netherlands (17) involving 3,123 people, not only was there no significant association seen in men, but also in women, there was a significant inverse association i.e. a lower risk in those who consumed coffee. Where a moderate association is sometimes observed in studies, it is possibly due to links with cigarette smoking and other factors known to increase the risk of developing cancer.

Q3. Bowel cancer is one of the most common forms of cancer. Is there any link with drinking coffee?

A.Several studies have found that coffee consumption is related to a lower risk of bowel cancer. According to one study in Canada, the risk reduced as coffee drinking rose to five cups a day (especially evident in men) (3). Another group of studies noted there was a 28% reduction in the risk of developing cancer of the lower bowel for those drinking four or more cups of coffee daily as compared to those drinking less than one cup (4).
There are a number of studies that did not reach this conclusion, but allowances were not made in those studies for other factors, such as smoking and alcohol consumption.

Q4. What are the reasons for this apparent protective effect?

A.Apart from increasing movement of food in the bowel, coffee is believed to help reduce the output of bile acids, which are known to play an active part in promoting cancer in the colon (6). Coffee also contains several compounds with strong antioxidant properties (such as caffeic acid and chlorogenic acid) (7, 8). Antioxidants are thought to play a significant role in protecting our cells and tissues from oxidative damage. Other compounds found in coffee - such as cafestol and kahweol - have anti-carcinogenic properties (9).

Q5. I saw reports some years ago that coffee caused cancer of the pancreas. Is that true?

A.Most experts do not now think there is a link. All the recent published studies strongly suggest no association between drinking coffee and increased risk of pancreatic cancer. These included the studies of 14,000 retired residents (12), the Health Professionals Follow-up Study (13) and the Nurses' Health Study cases.
Some years ago some studies showed a possible link but in one of those studies, when smoking was allowed for, the association with coffee was not considered statistically significant (14). One further study even found an inverse relationship, showing that the risk of developing pancreatic cancer was reduced in coffee drinkers (15).

Q6. How does drinking coffee help prevent liver cancer?

A.Various components of coffee have been related to such a positive effect, including caffeine, coffee oils kahweol of cafestol, and antioxidant substances from coffee, but no definite evidence is available.
However most scientists agree that it is probably the antioxidants in coffee, working in conjunction with caffeine, which results in this positive effect. Caffeine is already known to help protect against liver cirrhosis and given the weight of evidence from population studies, coffee appears to have a real effect in reducing the risk of liver cancer.

Q7. How much coffee do I need to drink for it to have a beneficial effect?

A.Most studies published in the past two decades have shown that in relation to bowel cancer the reduction in risk is apparent for those drinking at least 3-4 cups of coffee a day whilst for liver cancer studies have shown a beneficial effect after only 1-2 cups a day.

Q8. Are there any other major reports on coffee and cancer?

A.In a Norwegian study involving over 15,000 men and women (30) the authors concluded “The most important findings reported here are the lack of positive association between coffee drinking and any major cause of death and coffee not significantly increasing the incidence of any common cancer”

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