Drinking coffee halves the risk of liver cancer

Coffee consumption reduces the risk of liver cancer by approximately 50%, the results of a meta-analysis published in the online journal BMC Gastroenterology show. A total of 16 studies published before May 2012 were included in the analysis. Closer examination of the results suggested that the magnitude of the protective effective of drinking coffee was higher among men than women and also differed between patients of Asian and European origin. However, the authors do not believe their results are definitive and call for further research.

Liver cancer is an increasingly important cause of illness and death in both men and women. Infection with hepatitis B or C and excessive alcohol consumption are known risk factors for the malignancy. Factors protective against the development of liver cancer are uncertain, and the impact of coffee consumption is especially controversial.

A team of Chinese investigators therefore performed a meta-analysis of case-controlled and cohort studies examining the impact of coffee consumption and the risk of liver cancer.

Glossary

meta-analysis

When the statistical data from all studies which relate to a particular research question and conform to a pre-determined selection criteria are pooled and analysed together.

case-control study

An observational study in which a group of people with an infection or condition (called ‘cases’) are compared with a group of people without the infection or condition (called ‘controls’). The past events and behaviour of the two groups are compared. Case-control studies can help us understand the risk factors for having an infection or a condition. However, it is difficult both to accurately collect information about past events and to eliminate bias from case-control studies.

inclusion criteria

The conditions which a person must meet to join a research study.

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confounding

Confounding exists if the true association between one factor (Factor A) and an outcome is obscured because there is a second factor (Factor B) which is associated with both Factor A and the outcome. Confounding is often a problem in observational studies when the characteristics of people in one group differ from the characteristics of people in another group. When confounding factors are known they can be measured and controlled for (see ‘multivariable analysis’), but some confounding factors are likely to be unknown or unmeasured. This can lead to biased results. Confounding is not usually a problem in randomised controlled trials. 

antioxidant

A vitamin, mineral or drug which can reduce the activity of free radicals, the unpaired electrons produced as a consequence of burning energy in a cell.

Nine case-controlled and seven cohort studies met the investigators’ inclusion criteria. A total of eleven studies were conducted in Asia (nine in Japan) and five in Europe. All the studies provided data on the risk of liver cancer according to coffee consumption. However, there was little heterogeneity between the design of the studies. In particular, the level of coffee consumption against which the risk of liver cancer was assessed varied considerably, from as little as one cup each day to as many as eight or more daily cups.

Overall, the investigators found that a high coffee intake reduced the risk of liver cancer by 50% (OR = 0.50; 95% CI, 0.42-0.59). The protective effect of coffee consumption was similar in the case control studies (OR = 0.50; 95% CI, 0.40-0.63) and the cohort studies (OR = 0.48; 95% CI, 0.398-0.62).

Adjusting the results to take account of liver disease status provided similar results (OR = 0.54; 95% CI, 0.46-0.66).

“The results of the current meta-analysis…suggest that there is an inverse association between coffee consumption and liver cancer among different groups according to consumption level,” comment the investigators. “There were significant reductions of 50% in the risk of liver cancer with the highest consumption of coffee compared with non/almost never consumption.”

Stratifying the results by region suggested that the degree of protection provided by coffee consumption was higher in Asia (OR = 0.45; 95% CI, 0.36-0.56) than Europe (OR = 0.57; 95% CI, 0.44-0.75).

“The different results may be explained by racial differences,” suggest the authors. “Differences in coffee drinking habits may be a partial explanation for the discrepancy.”

Analysis according to sex showed that drinking coffee reduced the risk of liver cancer by 62% in men (OR = 0.38; 95% CI, 0.25-0.56) and by 40% in women (OR = 0.60; 95% CI, 0.33-1.10).

The authors note that caffeine has antioxidant properties, possibly explaining the protective effect of coffee consumption. However, the meta-analysis was unable to show the level of coffee consumption needed to provide protection against liver cancer.

“The results of this meta-analysis suggested that coffee consumption may be associated with a reduced risk of liver cancer,” the authors conclude. “However, because of potential confounding, this finding should be treated with caution. Further better-controlled studies are needed to confirm this finding.”

References

Sang L et al. Consumption of coffee associated with reduced risk of liver cancer: a meta-analysis. BMC Gastroenterology, doi: 10.1186/1471-1230X-13-34, 2013.