Coffee, good for everyone’s health… or almost so

An important review of the scientific literature on the health effects of coffee highlights the point: the drink protects against certain cancers and diseases. Only pregnant women should be wary of it

A journalist could spend his entire career writing articles about the health effects of coffee. Not a week goes by without the stimulating drink, one of the most widely consumed in the world, being the subject of dozens of scientific studies in specialized magazines. Google Scholar has no less than 382 articles with the title “coffee consumption” for the period from January to March 2018 alone!

However, this profusion of studies has not really made it possible to see more clearly, on the contrary. Announced carcinogenic on Monday, coffee protects against the disease according to another study published the next day, and so on. Scientific uncertainty sometimes leads to improbable political decisions: California may soon force coffee sellers to place health messages, as on cigarette packages, alerting consumers to the carcinogenic effects of the acrylamide in the drink… So, dangerous, coffee, yes or no? And what work can we rely on in this jungle?

A “super-study”

A recently published analysis has caught our attention. It was led by an international team led by the University of Catania in Italy and includes nutritionists, oncologists and epidemiologists, all independent of industry. The results of 127 meta-analyses, which are themselves based on a number of scientific articles on this subject, are examined in detail. A kind of “meta-meta-analysis”, or “super-study” on the effects of coffee, therefore. “This large-scale study reflects what the scientific literature considers valid about the effects of coffee,” says Astrid Nehlig, research director at the Institut national français de la santé et de la recherche médicale (Inserm), president of the Association pour la science et l’information sur le café and author of Café et santé – All about the many benefits of this beverage.

To say that coffee protects against cancer is debatable. To know which specific cancers are affected by coffee, more studies are needed.

Claude Pichard, doctor in charge of the nutrition unit at the HUG

Two main types of research were included in this work. First, there are so-called observational studies, which establish correlations between the diseases identified and coffee consumption. If you read somewhere that “drinking one cup of coffee a day increases the risk of prostate cancer”, there is a good chance that this is such a study. In this fictional example, the scientists obviously did not ingest coffee to volunteers to see if they developed cancer: they simply found – without establishing a causal link – that patients had statistically higher coffee consumption than healthy people.

The other category, which is much less numerous, concerns randomized controlled trials, gold standards for medical experimentation. In these trials, scientists give doses of coffee or caffeine to participants and then observe various variables (heart rate, blood pressure, respiratory rate, caffeine blood level…). Unlike observational studies, randomized controlled trials establish a causal relationship between the dose ingested and the observed phenomenon. But they are also much more difficult to conduct – and more expensive, hence their modest number.

Coffee protects against common cancers

By taking into account all these experimental devices, the authors wanted to paint the most complete picture possible. The analysis of this entire corpus enabled them to conclude that the largest coffee drinkers have a significantly reduced risk of cancer compared to others (small drinkers and abstinence, according to studies). The most dramatic decreases were in esophageal (-12%), prostate (-10%), or colon (-8%) cancers. However, the prize goes to pancreatic cancer, with a reduced risk of 25%. Results that leave Claude Pichard, doctor in charge of the nutrition unit at the University Hospitals of Geneva, skeptical. “To say that coffee protects against cancer is debatable. We now know that there is no single liver or breast cancer, but a multitude of variants, depending on the person. To know which specific cancers coffee causes, more studies are needed.”