A new study by scientists in Europe concluded that coffee drinking is linked to a reduced risk of primary liver cancer. But the findings do not say if coffee reduces liver cancer or if the link could be due to something else, for instance whether people with liver cancer tend to drink less coffee for other reasons.
The study was led by Francesca Bravi of the Istituto di Ricerche Farmacologiche Mario Negri in Milan, Italy, and is published in the August issue of Hepatology, the official journal of the American Association for the Study of Liver Diseases (AASLD).
Liver cancer is the fifth most common cancer and the third largest cause of death from cancer in the world, after lung and stomach cancer. According to the World Health Organization (WHO) liver cancer kills over 660,000 people globally every year.
In this latest study, Bravi and colleagues carried out a meta analysis of published scientific literature on the relation between coffee drinking and risk of hepatocellular carcinoma (HCC), which accounts for 90 per cent of liver cancers. A meta analysis is a way of pooling the data from several studies looking at the same relationship between variables to find out if they are saying something consistent.
The authors only included studies with quantitative information on coffee consumption and HCC incidence, and retrieved ten altogether covering a total of 2,260 cases of HCC. Six of them were case controlled studies from southern Europe and Japan (1,551 cases) and four of them were cohort studies from Japan (709 cases).
They found that among coffee drinkers overall, there was a 41 per cent reduction in risk of HCC compared to those who never drank coffee. The reduced risk of HCC among coffee drinkers was also evident for people in Japan, who drink less coffee than people in southern Europe.
For low or moderate coffee drinkers the reduced risk of HCC was smaller (30 per cent) and for high coffee drinkers the risk reduction was higher (55 per cent).
Overall they found that an increase of 1 cup of coffee per day was linked to a reduced HCC risk of between 23 and 25 per cent (23 per cent in case controlled studies and 25 per cent in cohort studies).
The results were the same even after adjusting for potential confounding factors, such as liver cirrhosis, hepatitis B and C, social class, alcohol intake and smoking status.
Bravi and colleagues suggest that coffee drinking has also been linked to reduced risk of other liver diseases and this link to reduced HCC could be related to that.
They also said research on the chemicals in coffee has shown that some of them have beneficial effects on the liver, this includes caffeine, and coffee has also been linked with a reduced risk of liver diseases such as cirrhosis. However, animal and laboratory studies have found that certain other compounds in coffee interfere with the detoxification of carcinogens and therefore have a negative effect on the liver. So it is not simply a case of more coffee is better for the liver.
Bravi and colleagues cautioned that while they found evidence of a link between coffee drinking and reduced risk of HCC, they are not suggesting that drinking coffee is the cause of reduced liver cancer. As a for instance they say it’s possible that when people learn they have a liver problem they reduce their coffee intake, although they are careful to point out this is not routinely recommended.
A limitation of their findings is that most of the coffee consumption records were based on self reports they said, but the fact the studies from southern Europe and Japan showed the same relationship between coffee drinking and reduced risk of HCC suggests lack of bias in the studies.
The authors concluded that:
“The present analysis provides evidence that the inverse relation between coffee and HCC is real, though inference on causality remains open to discussion.”
Related reading: Drinking Coffee: More Good Than Harm? (9 July 2012).
Written by: Catharine Paddock