Coffee – friend or foe?

It’s no secret that we Brits like a brew. Yes, we are partial to a cup of tea (and maybe the occasional pint) but increasingly it seems, our passion is coffee. Fashionable coffee shops, teeming with jittery customers and their glowing laptop screens are replacing High Street pubs across the UK.1

Caffeine is the most widely-used psychoactive substance in the world.2 With its ‘safe-for-work’ buzz and uniquely complex taste, coffee is the most socially acceptable of addictions. Given that we consume around 2.25 billion cups of coffee per day globally, even small health effects may be important at the population level.3

“Coffee can help you lose weight!”, says the Independent.4 Such is the volume of coffee content online, a brief search can attach almost any chosen health benefit or risk to the bittersweet bean. Fortunately, academics prefer coffee to sleep, so it should come as no surprise that there is a growing body of scientific literature exploring its health effects.

In the largest study to date, Poole and colleagues explored the effects of coffee consumption on multiple health outcomes and published their results in the BMJ in late 2017.5 This study is best described as a ‘review of reviews’ and draws on the results of 218 meta-analyses.* Poole’s conclusions emerge from the combined results of 17 meta-analyses of randomised studies,** as well as 201 meta-analyses of observational studies. Observational studies are generally considered lower in the hierarchy of scientific evidence than interventional studies such as randomised studies. One issue with observational research is that it can be difficult to establish whether drinking coffee actually CAUSES a particular health outcome, or whether the health outcome is in fact linked to drinking coffee in some other way (e.g. being wealthier).

So what did the study find?

Overall, Poole’s results provide strong evidence that drinking three to four cups of coffee per day is very likely to be safe. In fact, the study suggests that this level of coffee consumption is more likely to benefit our health than cause harm. Poole found that drinking three to four cups of coffee is associated with a 30% reduction in type 2 diabetes, a 18% reduction in cancer, a 15% reduction in cardiovascular disease and a 17% reduction in death from any cause, when compared to drinking no coffee. However, drinking coffee was associated with harm in pregnancy. Links were found between coffee consumption and low birth-weight, premature birth and miscarriage. Women who drank coffee were also at greater risk of fractures than those who didn’t.

The results of this study are exciting (especially for baristas who enjoy a sales pitch) but, of course, they don’t tell the whole story. Yes, coffee is rich in anti-oxidants, but if you pile sugar and cream into your brew and expect to lose weight, you’re probably not going to get a refund. In terms of sleep hygiene, drinking a cup of coffee at bedtime is something akin to washing your hands in the toilet. If you are prone to feelings of anxiety then a nice, strong cup of coffee is unlikely to reduce them. However, if you are sitting down to write a lengthy work assignment, why not take some advice from the academics and put the kettle on?

*A meta-analysis is a powerful method of statistical analysis that combines the results of multiple scientific studies.

**In a randomised trial, participants are assigned to a treatment group at random; for example, drinking either five cups of coffee per day or none at all. Random allocation ensures that the coffee guzzlers, as a group, are broadly comparable to the non-coffee drinkers. Observational studies are not randomised – in fact these studies do not assign participants to any particular treatment at all. While observational studies can be useful, they rarely provide definitive answers to questions of safety or effectiveness.


This article is for information only and should not be used for the diagnosis or treatment of medical conditions. myHealthSpecialist makes no representations as to the accuracy or completeness of any of the information in this article, or found by following any link from this article. Please consult a doctor or other healthcare professional for medical advice.

Dr Paul Welford is a medical doctor, writer/researcher and former-physiotherapist