Coffee appears to confer a number of protective effects against liver disease.
Increasing coffee consumption by two cups per day was found to reduce the risk of cirrhosis by nearly half, as reported in a meta-analysis of studies of cirrhosis patients stratified by coffee consumption. A subset of the studies also showed a clinically relevant dose-response between coffee and hepatocellular cancer (HCC).
While earlier research observed an inverse association between coffee consumption and liver cancer, this was the first evidence that indicates coffee may have a protective effect against cirrhosis, the most important risk factor for HCC.
While caffeine is an important factor in this protective effect, coffee comprises more than a thousand compounds, many of which are biologically active and may also affect human health. These compounds include chlorogenic acid, kahweol, and cafestol, all of which are anti-oxidative and anti-inflammatory agents.
Because coffee is ubiquitous in most cultures, its effects on human health have been studied extensively. The biological effects of coffee include stimulation of the central nervous system primarily by caffeine, the attenuation of oxidative stress and inflammation, and anti-carcinogenesis.
In the context of liver disease, coffee appears to confer a number of protective effects. Animal studies and human observational studies suggest coffee consumption reduces the frequency of abnormal liver function tests, fibrosis, cirrhosis, and HCC.
Studies and Analyses
The meta-analysis included studies published until July 2015 that reported odds ratios, relative risks (RR) or hazard ratios (HR) for cirrhosis stratified by coffee consumption. The study calculated RRs of cirrhosis for an increase in daily coffee consumption of two cups for each study and overall.
Analyses by study design, type of cirrhosis, and mortality were calculated. The researchers also assessed the risk of bias in each study and the overall quality of evidence for the effect of coffee on cirrhosis.
Protective Mechanisms of Caffeine
It is biologically plausible that coffee protects the liver against the inflammatory and fibrotic process leading to cirrhosis. Caffeine is thought to be important, as animal studies show that non-coffee caffeine protect against toxin-induced liver fibrosis. The protective mechanism of action in caffeine may be via antagonism of the adenosine receptor A2aAR.
Caffeine might also attenuate fibrosis by suppression of inflammation and oxidative stress. Caffeine inhibits tumor necrosis factor-a, a pro-inflammatory cytokine and reactive oxygen species production by Kupffer cells.
Protective Effects of Other Components of Coffee
There is evidence that other non-caffeine-mediated mechanisms also contribute to the protective effect seen from coffee. There is some epidemiological evidence that decaffeinated coffee protects against cirrhosis and abnormal liver function tests.
In animal studies, decaffeinated coffee also protected against toxin-induced fibrosis. The evidence for decaffeinated coffee protecting against cirrhosis is weaker overall than for regular coffee, but there is still biological plausibility.
The findings of this meta-analysis are important given the high incidence of severe liver disease. The next steps should be to develop interventions that support patients at risk of, or with mild-to-moderate chronic liver disease (CLD), to increase their coffee consumption.
Given the dose-response relationship between coffee and CLD, these interventions could benefit even existing coffee drinkers.