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Coffee more likely to benefit than to harm health

Three or four cups daily probably best ‘dose’ – but not in pregnancy or high fracture risk

Louise Prime

Thursday, 23 November 2017

People who drink three to four cups of coffee a day have a lower risk of death and of heart disease than people who drink no coffee, as well as being at lower risk of several other diseases, UK researchers have found. Their study,* published today in The BMJ, concluded that coffee is safe at usual levels of consumption – except for women who are pregnant or at risk of fracture – but experts noted that the evidence is not strong enough that people who don’t already drink coffee should start doing so.

Researchers led from the University of Southampton Faculty of Medicine conducted an ‘umbrella review’ of the evidence across meta-analyses of observational and interventional studies of coffee consumption and any health outcome; they identified 201 meta-analyses of observational research with 67 unique health outcomes and 17 meta-analyses of interventional research with nine unique outcomes.

They reported that coffee consumption was more often associated with benefit than harm for a range of health outcomes across exposures including high versus low, any versus none, and one extra cup a day. There found evidence of a non-linear association between consumption and some outcomes, with summary estimates indicating largest relative risk reduction at intakes of three to four cups a day versus none, including all-cause mortality (relative risk RR 0.83), cardiovascular mortality (RR 0.81), and cardiovascular disease (RR 0.85). High versus low consumption was associated with an 18% lower risk of incident cancer (RR 0.82). Consumption was also associated with a lower risk of several specific cancers and neurological, metabolic, and liver conditions.

The study authors reported that harmful associations were largely nullified by adequate adjustment for smoking – except in pregnancy, where high versus low/no consumption was associated with low birth weight (odds ratio OR 1.31), preterm birth in the first (OR 1.22) and second (OR 1.12) trimesters, and pregnancy loss (OR 1.46). There was also an association between coffee drinking and risk of fracture in women, but not in men.

Decaffeinated coffee was beneficially associated with all-cause and cardiovascular mortality in a similar way to caffeinated coffee; marginal benefit in the association between decaffeinated coffee and cancer mortality did not reach significance. The study authors commented: “Importantly, there were no convincing harmful associations between decaffeinated coffee and any health outcome.”

They concluded: “Coffee consumption seems generally safe within usual levels of intake, with summary estimates indicating largest risk reduction for various health outcomes at three to four cups a day, and more likely to benefit health than harm. Robust randomised controlled trials are needed to understand whether the observed associations are causal. Importantly, outside of pregnancy, existing evidence suggests that coffee could be tested as an intervention without significant risk of causing harm. Women at increased risk of fracture should possibly be excluded.”

The author of a linked editorial,** added that although this study provides reassurance that coffee intake is generally safe, doctors should not recommend drinking coffee to prevent disease; nor should people start drinking coffee for health reasons. He also pointed out that coffee is often consumed with products rich in refined sugars and unhealthy fats that “may independently contribute to adverse health outcomes”.

But he concluded: “Moderate coffee consumption seems remarkably safe, and it can be incorporated as part of a healthy diet by most of the adult population.”

* Poole R, Kennedy OJ, Roderick P, et al. Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes. BMJ 2017; 359: j5024 doi: 10.1136/bmj.j5024

** Guallar E. Coffee gets a clean bill of health. BMJ 2017; 359: j5356 doi: 10.1136/bmj.j5356

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