California, Coffee and Cancer | The Body of Evidence

California, Coffee and Cancer

My article from the Montreal Gazette looking at whether coffee really does need a warning label.


Recently a California judge ruled that coffee increases the risk of cancer and must carry a warning label. The decision came as a result of a lawsuit filed against companies like Starbucks claiming they violated the state's Safe Drinking Water and Toxic Enforcement Act(popularly known as Prop 65) that requires warning labels for any food that contains a chemical that may cancer.

The main argument in the lawsuit is that coffee contains acrylamide, which is on the list of chemicalsthat the state of California says are carcinogenic. While acrylamide is used in a number of industrial processes, it also occurs naturally in our food. When starchy foods are heated to a high temperature, the sugar and amino acids combine to form acrylamide. Baked, roasted or fried food is more likely to create acrylamide than food that is boiled, steamed or microwaved.

The discovery in 2002 that acrylamide is present in certain foods was concerning. It can be found in french fries and potato chips, although no one thought these foods were all that healthy in the first place. But acrylamide can also be found in bread, grain products and, of course, coffee, which is why the lawsuit was filed.

In high doses, acrylamide can be toxic. But this toxicity is based on studies where the acrylamide fed to lab rats and mice is roughly 1,000-10,000 times what people would be exposed to in food. Data linking acrylamide in food to cancer is lacking.

Nevertheless, the plaintiffs won their case. The judge's ruling said that the defendants had not met the burden of proof required to prove that coffee was safe or beneficial.

I am baffled, truly and utterly baffled.

There is actually a wealth of human data suggesting coffee is either neutral or possibly beneficial in terms of cancer risk. A 2017 meta-analysis in the BMJ found the evidence suggested coffee either had no effect or was mildly protective for many forms of cancer.

Claiming that coffee protects you against cancer may be overstating the case. These studies are observational, and not randomized trials, however it seems very clear that there is no signal for harm. There are two exceptions that deserve attention, however. There have been studies suggesting that coffee consumption is linked to an increase risk of lung and bladder cancer.

The explanation probably has to do with smoking and the concept of confounding. Smoking increases the metabolism and clearance of caffeine from the body, which may explain why smokers tend to drink more coffee than non-smokers. Smoking also increases the risk of cancer, particularly lung and bladder cancer. Therefore, smoking serves as confounder, a variable tied to both coffee drinking and cancer risk, and it makes it seem as if coffee is carcinogenic. Adjusting for smoking mitigates that risk.

The wealth of scientific data argues against coffee as a risk factor for cancer. To label it as such is, in my mind, ridiculous. Coffee has always contained (very low doses) of acrylamide as a consequence of the roasting process. Acrylamide in high doses is toxic; the drinking of coffee is not.

The consequence of repetitive health scares like "cell phones cause cancer" and "smoked meat is as dangerous as smoking" have unfortunately left the public numb to health news. People now cynically say that everything causes cancer. The problem with putting warning labels on everything is that eventually people just ignore the labels.

I am also worried that questions of science are being decided in courtrooms rather than research labs. By the same token, doctors and scientists should not start practising law. Too many innocent people wouldend up in jail, and too many harmless things would become labelled as dangerous.





Photo: from courtesy of Jeff Chiu/AP