Can Coffee Prevent Chronic Liver Disease?
Recent headlines (1,2) attest that drinking coffee prevents chronic liver disease, based on a recently published study (3). The PEN Team set out to investigate whether the evidence supports these cause-and-effect statements.
The study, published in the Journal of BMC Public Health, looked at 384,818 coffee drinkers and 109,767 non-coffee drinkers against estimated hazard ratios (HR) of incident chronic liver disease (CLD), incident CLD or steatosis, incident hepatocellular carcinoma (HCC) and deaths from CLD over a 10-year period (3). The authors concluded that “…the finding that all types of coffee are protective against CLD is significant given the increasing incidence of CLD worldwide and the potential of coffee as an intervention to prevent CLD onset or progression”.
This study’s findings (3) should be considered low certainty evidence (the true effect may be quite different from the estimated effect (4)). With only low certainty evidence, the PEN Team questions whether any recommendations should be made on the basis of this research. Since there isn’t high certainty evidence, a recommendation for people to consume coffee to prevent CLD cannot be made.
Why is this research low certainty evidence?
The main reason that this study’s findings are low certainty evidence is due to serious study limitations, primarily based on its observational design. The research participants were not randomized for coffee consumption. The participants chose their coffee consumption and then described it to researchers.
It is possible that the protective factor attributed to coffee is actually something else. People choose their lifestyles and food choices based on many factors. In this type of study, the observed relationship could be due to some other factor that is common among people who drink coffee. The study authors adjusted their findings for some important CLD predictors (including alcohol-related liver disease, BMI, alcohol intake, diabetes and smoking); however, there may be some other factor(s) that they did not adjust for that could be the actual causal factor(s).
Other weaknesses that raise concerns about how much confidence should be put in this study’s findings are (3):
- There was no clear dose-response effect, and the researchers did not perform a statistical test to check for a dose-response effect of better outcomes associated with higher coffee consumption.
- The study used self-reported, single measurements only of coffee, alcohol and tobacco intakes (3). Due to social desirability bias, people do not always accurately report their intakes (5).
- The study did not provide information on associations with coffee consumption and the various causes of CLD (3). For example, perhaps people who drink more coffee are less likely to be exposed to a virus that causes CLD.
- Although this represents a large cohort of 500,000 participants, this study was at risk of selection bias since only about 10% of those invited to participate agreed to participate.
The PEN Team is concerned that the research paper title, “All coffee types decrease the risk of adverse clinical outcomes in chronic liver disease”, may imply that this is high quality research. The media made cause-and-effect headlines, including that coffee “cuts risk”, “reduces your risk”, “may help avoid chronic liver disease” (1,2). A better title would be: Potential association of coffee consumption with reduced risk of CLD, which matches the study’s conclusion.
Other meta-analyses of observational studies have suggested that coffee consumption is inversely associated with lower rates of liver cancer (6) and non-alcoholic fatty liver disease (NAFLD) (7). This cohort study expanded this association to all types of coffee, including decaffeinated coffee (3).
Given the limitations of these observational studies, international caffeine guidelines
should be followed to guide coffee consumption. It would be important for future research to consider additional non-liver outcomes to ensure that recommendations can be safely made to use coffee as a preventive agent for liver diseases.
See Additional Content:
- LaMotta S. Drinking coffee of any type cuts risk for liver problems, study says. CTV News. 2021 Jun 22. Available from: https://www.ctvnews.ca/health/drinking-coffee-of-any-type-cuts-risk-for-liver-problems-study-says-1.5480329
- Charles K. Drinking coffee or decaf may help avoid chronic liver disease. NewScientist. June 22, 2021 Jun 22. Available from: https://www.newscientist.com/article/2281765-drinking-coffee-or-decaf-may-help-avoid-chronic-liver-disease/
- Kennedy OJ, Fallowfield JA, Poole R, Hayes PC, Parkes J, Roderick PJ. All coffee types decrease the risk of adverse clinical outcomes in chronic liver disease: a UK Biobank study. BMC Public Health. 2021 Jun;21(1):970. https://doi.org/10.1186/s12889-021-10991-7. Abstract available from: https://pubmed.ncbi.nlm.nih.gov/34154561/
- Siemieniuk R, Guyatt G. What is GRADE? BMJ best practice toolkit. 2021. Available from: https://bestpractice.bmj.com/info/toolkit/learn-ebm/what-is-grade/
- Graeff TR. Response bias. In the Encyclopedia of Social Measurement. 2005. Available from: https://www.sciencedirect.com/referencework/9780123693983/encyclopedia-of-social-measurement
- Bhurwal A, Rattan P, Yoshitake S, Pioppo L, Reja D, DellatoreInverse P, et al. Association of Coffee with Liver Cancer Development: An Updated Systematic Review and Meta-analysis. J Gastrointestin Liver Dis. 2020 Sep 9;29(3):421-8. doi: 10.15403/jgld-805. Abstract available from: https://pubmed.ncbi.nlm.nih.gov/32830818/
- Chen YP, Lu FB, Hu YB, Xu LM, Zheng MH, Hu ED. A systematic review and a dose-response meta-analysis of coffee dose and nonalcoholic fatty liver disease. Clin Nutr. 2019 Dec;38(6):2552-7. doi: 10.1016/j.clnu.2018.11.030. Epub 2018 Dec 4. Abstract available from: https://pubmed.ncbi.nlm.nih.gov/30573353/