MedicalResearch.com: What is the background for this study?
Response: Worldwide, over two billion cups of coffee are consumed every day. Since such a lot of coffee is consumed it is important to understand whether this is beneficial or harmful to our health. Evidence to date has been mixed and this tends to vary between different outcomes.
Coffee is a complex mixture of many bioactive compounds including caffeine, chlorogenic acids, and diterpenes. Laboratory experiments have previously highlighted the potential for coffee to have anti-oxidant, anti-inflammatory, anti-fibrotic and anti-cancer effects.
Our research group is interested in liver conditions and we were aware of studies suggesting beneficial associations between drinking coffee and liver disease. We went on to conduct two meta-analyses and concluded that coffee drinking was beneficially associated with both liver cirrhosis and liver cancer.
Existing research is mainly observational and prone to the effects of confounding which can sometimes falsely lead to apparent associations, both beneficial and harmful. To overcome these limitations we plan to conduct a randomised controlled trial to investigate coffee as a potential treatment for diseases of the liver.
However, before we begin giving patients coffee as a treatment as part of a research trial, we wanted to understand what existing evidence there was for harm. This led us to conduct the umbrella review. An umbrella review is a review of other higher-level evidence and tries to systematically bring this evidence together and draw conclusions.
MedicalResearch.com: What are the main findings?
Response: Drinking coffee was more frequently associated with benefit than harm to health across different categories of consumption. Headline benefits included a lower risk of death from any cause, death from heart disease, or developing heart disease in the first place. For these outcomes most benefit was seen at intakes of between 3 and 4 cups per day. Importantly, higher intakes were not associated with harm, but the benefit was less pronounced.
Drinking coffee was also associated with lower risk of incident cancer and for cancer of the prostate gland, womb, skin and oral cavity. Lower risks were also seen for type II diabetes, metabolic syndrome, gallstones, renal stones and gout. It was also associated with lower risk of Parkinson’s disease, depression and Alzheimer’s disease. Overall, greatest benefit was seen in the associations of coffee drinking and diseases of the liver.
Our review also highlighted some potential harms of coffee. Some of these are already widely known such as the harmful effects of too much caffeine during pregnancy that our review highlighted were associated with low birth weight, preterm birth within the first and second trimester, and pregnancy loss. Recommendations for limiting caffeine during pregnancy are widely accessible.
We also highlighted a small increase risk of fracture in women but not in men. This gender difference may have some biological plausibility but the evidence has some discrepancies and further studies to look at this are required before drawing firm conclusions.
MedicalResearch.com: What should clinicians and patients take away from your report?
Response: Aside from pregnancy, moderate coffee drinking, in the region of 3-4 cups per day, is more likely to benefit health than harm it. People should not start drinking coffee or increase their intakes based on the findings in our umbrella review, due to the limitations in the types of evidence that were used. This is mainly due to the potential for other factors associated with coffee drinking and health outcomes to have falsely led to the associations seen.
MedicalResearch.com: What recommendations do you have for future research as a result of this study?
Response: Future research could include randomised controlled trials where coffee is given as a treatment for an outcome of interest. This has particular relevance to liver diseases, such as liver cirrhosis, which appear to have the greatest benefits from coffee, and for which the current therapeutic options are limited.
Mendelian Randomisation studies could also be used to investigate whether there is genetic evidence for the association between coffee drinking and some outcomes, especially for the apparent small increase risk from coffee drinking and fracture in women.
Disclosures: The study received no specific funding. None of the authors have any connection with organisations linked to the coffee industry.
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Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes
BMJ 2017; 359 doi: https://doi.org/10.1136/bmj.j5024
(Published 22 November 2017)
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