A new study finds that drinking three to four cups of coffee a day is tied to a lower risk of heart disease and death compared to drinking no coffee at all. Coffee consumption is also associated with a lower risk of some cancers, diabetes, liver disease, and dementia.
On the downside, however, drinking coffee may be linked to a very small increased risk of fracture in women and may be associated with some harms if consumed during pregnancy.
For the study, a research team led by Dr. Robin Poole, Specialist Registrar in Public Health at the University of Southampton in the UK, with colleagues from the University of Edinburgh, conducted an umbrella review of 201 observational studies as well as 17 studies that had collected data from clinical trials across all countries and all settings.
The findings show that coffee consumption was consistently associated with a lower risk of death from all causes and from heart disease, with the greatest reduction in relative risk of death at three cups a day, compared with non-coffee drinkers.
Coffee was also tied to a lower risk of several cancers, including prostate, endometrial, skin, and liver cancer, as well as type II diabetes, gallstones, and gout. The greatest benefit was seen for liver conditions, such as cirrhosis of the liver.
Finally, the researchers also found beneficial associations between coffee consumption and Parkinson’s disease, depression, and Alzheimer’s disease.
Drinking more than three cups a day was not associated with harm, but the beneficial effect was less pronounced.
The included studies used mainly observational data, so no firm conclusions can be drawn about cause and effect, but the findings back up other recent reviews and studies of coffee consumption.
Many of the included studies may have adjusted for factors that may be associated with both the health outcome and with coffee drinking, such as smoking. This was not comprehensive and varied from study to study. The authors can therefore not rule out the effect of such factors on the apparent harmful or beneficial associations.
The authors conclude that coffee drinking “seems safe within usual patterns of consumption, except during pregnancy and in women at increased risk of fracture.” And they call for robust randomized controlled trials “to understand whether the key observed associations are causal.”
In a linked editorial, Eliseo Guallar at the Johns Hopkins Bloomberg School of Public Health says that until it can be proven that coffee intake is generally safe, doctors should not recommend drinking coffee to prevent disease — and people should not start drinking coffee for health reasons.
Furthermore, coffee is often consumed with products rich in refined sugars and unhealthy fats, “and these may independently contribute to adverse health outcomes,” Guallar said.
However, even with these warnings, “moderate coffee consumption seems remarkably safe, and it can be incorporated as part of a healthy diet by most of the adult population,” he said.
The research is published in the journal The BMJ.