Case-control studies, mainly based in Europe, have linked more coffee to less colorectal cancer, with a meta-analysis of 12 such studies reporting high coffee consumption could reduce the risk by 28 per cent.
This result has not been backed up by prospective cohort studies, including a small earlier study by the same Swedish researchers (Gut, 2001, Vol. 49, pp. 87-90).
The new study, published on-line in the American Journal of Epidemiology (doi: 10.1093/aje/kwj067), used data from two population-based cohort studies: the Swedish Mammography Cohort (61,433 women) and the Cohort of Swedish Men (45,036 men).
From 1987-1990 and followed through 2004, 1,279 cases of colorectal cancer were diagnosed. The volunteers drank an average of three cups of coffee per day, half a cup less than the US average.
Although the researchers recorded that the people who drank the most coffee were also more likely to be smokers and to use multivitamin supplements much less, there was no link between coffee drinking and the cancer.
"A higher level of coffee consumption (greater than six cups per day) was not significantly associated with colorectal cancer risk. The pooled rate ratio for six or more cups of coffee per day as compared with less than one cup per day was 1.04," wrote lead author Susanna Larsson from the Karolinska Institutet in Stockholm.
"Our null finding for coffee consumption… is consistent with a report combining data from two large US cohort studies - the Nurses' Health Study and the Professionals Follow-up Study," said Larsson.
The researchers claim that the study design effectively eliminated any recall bias and, by following-up the Swedish Mammography Cohort, any changes in coffee consumption were accounted for.
No comment could be given on different types of coffee however, but claims that decaffeinated coffee is very uncommon in Sweden led the scientists to limit their claims to filtered coffee.
While coffee and caffeine appear to have no effect on colorectal cancer, recent research has claimed that caffeine could reduce the risk of liver disease, and can also boost short-term memory.
The beneficial aspects of coffee are linked to their high content of phenolic compounds with antioxidant properties. University of Scranton researchers recently calculated that coffee is the main source of antioxidants for the average American.
According to the National Institute of Cancer, colorectal cancer is the third most common cancer in the US. The cost of colorectal treatment in the US was estimated to be $8.4 billion in 2004.