When it comes to coffee and cancer, there are two questions which most Canadians want answered: Does coffee cause cancer? Will drinking coffee help prevent cancer?

As coffee is one of the most studied substances worldwide, with more than 20,000 studies looking at its general effects, the coffee and cancer connection has been studied extensively. Currently, scientists are able to state conclusively that coffee does not cause cancer with almost universal consensus.

This general consensus is a turnaround from positions several decades ago, when early studies indicated that coffee may have cancer-causing properties. However, these have since been discredited as being poorly designed, not isolating coffee drinkers from smokers, for example, and essentially flawed in their conclusions.

As such, upon further view and study, various international cancer organizations have stated unequivocally that there is no connection between coffee consumption and cancer. The Canadian Cancer Society, for example, states that there is no evidence that coffee or caffeine increases the risk of cancer.

What's more, evidence is mounting that coffee consumption appears to have a preventative role in certain cancers although it is unclear whether this effect is seen across all types. Numerous credible and well-publicized studies have concluded that coffee drinkers are less inclined to develop specific types of cancer, with the most notable evidence mounting in the following:

Liver cancer
Breast cancer
Colon cancer

The most recognized theory on why coffee has a role in cancer prevention is that the beverage's high antioxidant content (link to antioxidant section) is providing a protective effect. For North Americans, coffee is the largest daily source of antioxidants, followed by tea and a variety of fruits and vegetables.

As a major international medical concern, research into understanding the causes and prevention of cancer is continually evolving. Countless studies have examined nutritional aspects of prevention, including how coffee drinkers fare versus non coffee drinkers. Coffee has emerged as having a potential preventative role in a number of specific cancers, including the following where the most compelling evidence has been found:

A large scale study followed 90,000 Japanese subjects over ten years and concluded that coffee drinkers have half the risk of developing liver cancer as non coffee drinkers. Published in the Journal of the National Cancer Institute in 2005, the study showed this effect for those who drank just one to two cups daily with the effect increasing at three to four cups(ref)

A Canadian-lead study of 1,700 women with BRCA gene mutations looked at the effect of coffee consumption and breast cancer on this group who are already at high risk. For women with the BRCA1 gene who were also heavy coffee drinkers, averaging six or more cups a day, results were dramatic with about a 75 per cent reduction in risk of breast cancer. At moderate coffee consumption levels, results were also promising with a 10 per cent reduction for one to three cups per day and 25 per cent for four to five cups. The study results were published in January, 2006 in the International Journal of Cancer.(ref)

Coffee may also help protect against colon cancer, with a key study showing that three to four cup a day coffee drinkers cut their risk by 27 per cent versus non drinkers. The Italian study, published in the International Journal of Cancer in 1997, included controls for smoking, family history, BMI and diet to effectively isolate coffee's effect.(ref) Another major study, published in the American Journal of Epidemiology in 1998 showed similar results with a 28 per cent risk reduction.(ref)

Lois Ferguson

Will drinking coffee cause cancer?

The Canadian Cancer Society advises Canadians that there is no evidence that coffee or caffeine increases the risk of cancer. So go ahead and enjoy your daily coffee. In fact, you might even be doing yourself some good. An emerging body of evidence is showing that coffee consumption may have a role in certain types of cancer. For example, studies have shown that risk of liver cancer may be cut in half for coffee drinkers.