With so many contradicting headlines declaring the devastating health effects of coffee or its limitless health benefits, it can all get very confusing. Fortunately, there is now enough data available for us to begin unpicking the truth. That is what researchers from the universities of Southampton and Edinburgh have set out to do. They have recently completed an umbrella review – systematically searching through previously published meta-analyses to look for overarching trends on the health benefits and risks of coffee consumption to make informed choices on future research directions.
Over 200 meta-analyses were included in the study, most of which were observational, meaning cause and effect were not directly measured. Studies were excluded if they did not have enough information in them, did not contain a meta-analysis, or focused on genetic variations affecting caffeine metabolism. The studies were assessed for the quality of the methodology and results obtained.
The results showed health benefits in a range of areas, including, most notably, in liver disease, Alzheimer’s disease, type 2 diabetes and certain cancers. Overall risk of mortality was reduced by 10%. Health risks were primarily associated with complications in pregnancy, including increased risk of low birth weight, premature birth and miscarriage. There was also an increased risk of childhood leukemia if a mother had drunk more coffee during pregnancy and an increased risk of fractures in women already at risk. Other health outcomes studied were not found to be significantly affected by coffee consumption. Optimum health benefits were reached by drinking between 3 and 5 cups of coffee a day. Whilst more cups of coffee didn’t increase the risk of harm, the health benefits observed did not increase dramatically.
As coffee is a complex mixture of over 1000 chemicals it is difficult to determine exactly what it is that is good or bad for you. However, the researchers suggested it is the antioxidants in coffee are the most likely to be responsible. Caffeine is not thought to be the magic ingredient, as they found that decaffeinated coffee produced comparable results to caffeinated coffee. It is also believed that the filter used in filtered coffee captures these antioxidants and this may be why fewer health benefits were seen in filter coffee compared to other types.
The methodologies included in the meta-analyses studied were quite wide ranging and did not account for things such as cup size, bean type, or the preparation or type of coffee (e.g. Americano vs. Latte). Filter coffee, for example, has more caffeine in it than instant coffee and many people add cream or sugar which may negate the positive effects of the coffee, particularly for things such as type 2 diabetes. The studies included were also found to be of low or very low quality and the researchers have recommended more randomized control trials to be undertaken to strengthen and confirm the results. So, should you start drinking coffee for your health? The verdict is no, but if you are already hooked you aren’t doing yourself much harm.
This article was written by Michael Mabbott and edited by Bonnie Nicholson.