After fending off negative health claims made against coffee for decades, the industry was vindicated last month when a controversial cancer research group changed its mind about classifying America’s favorite caffeine beverage as a possible carcinogen.
“The latest ruling on coffee reflects decades of cumulative positive research and review,” a National Coffee Association spokesperson told Legal Newsline. “It's still too early to tell whether the latest findings will have an impact on the coffee industry going forward, but we're happy to see the science publicly supported.”
The International Agency for Research on Cancer (IARC), a component of the World Health Organization, made headlines for its reversal on coffee, but its initial evaluation flew under the radar in 1991.
Geoffrey Kabat, an epidemiologist at the Albert Einstein College of Medicine in New York, doesn’t remember it, and he did studies on coffee and bladder cancer in the 1980s.
“I think these kinds of announcements get more attention nowadays because of people’s concern with anything that might affect their health and, of course, because of the internet and social media,” Kabat told Legal Newsline. “But I doubt if these ‘scary’ announcements — like the recent one regarding processed meat and red meat — have much effect on people’s actual behavior.”
Coffee consumption in the U.S. has been steady since 1999, according to a Gallup poll. In 2015, 64 percent of those surveyed said they drink one or more cups of coffee each day. In 1999, it was 63 percent. On average, coffee drinkers indulge in about three cups each day. The number of coffee shops rose 40 percent between 1999 and 2005.
The impact of a carcinogen label can impact a product more than just sales. As IARC has gained more attention for its work, plaintiff attorneys have used the results to launch personal injury suits against the makers of a variety of products.
Since IARC classified the herbicide glyphosate as a probable carcinogen, several lawsuits have been filed against its maker Monsanto.
The Council for Education and Research on Toxics sued Starbucks and other coffee chains in California in 2014 for not informing customers that its products contain a substance recognized as carcinogenic: acrylamide, a chemical that results from cooking certain foods above 120 degrees Fahrenheit — this includes roasted coffee beans. As a result of the litigation, Starbucks started posting signs warning customers that coffee and baked goods contain acrylamide.
IARC classified acrylamide as “probably carcinogenic” in 1994. However, experts say humans are unlikely to be exposed to a high enough dose to cause problems.
"You would have to drink probably over 100 cups of coffee a day in order to get to that dangerous dose, so it is totally absurd,” Stanley Omaye, a professor of nutrition and toxicology at the University of Nevada, told Chemistry World in 2014.
Critics of IARC say the agency does a poor job because it measures hazard, not risk; it also employs a confusing method for classifying substances that they say actually detracts from other research on causes of cancer.
IARC classifies substances into four broad categories:
Group 1 is for those substances considered carcinogenic to humans, including cigarette smoke, alcohol, asbestos and, a recent addition, processed meats. Group 2 is split between substances that are probably carcinogenic and those that are possibly carcinogenic. In 1991, coffee fell into the second classification in this group. Group 3 is like a shoulder shrug. The substances included here are deemed “not classifiable.” That’s where coffee sits right now, joining about 500 other substances.
After evaluating nearly 1,000 substances, IARC has classified only one substance as “probably not carcinogenic to humans” — its Group 4. That substance is a chemical called caprolactam, which is used to make nylon.
This wouldn’t mean much if IARC’s evaluations still got little attention, like with coffee in the ‘90s.
“What has changed, I think, is that people did not pay as much attention 20 and more years ago to this sort of publication,” Kabat said. “And scientists and agencies didn’t try to get attention by issuing press releases.”
He said IARC’s re-evaluation of coffee was long overdue. Study methods have improved over the years and the link between coffee and cancer has been a popular topic. Reviews of the hundreds of coffee studies actually show coffee is linked with a lesser risk of several cancers, including colorectal, liver and postmenopausal breast cancer.
“The 1991 assessment was based on pretty poor studies, so the evidence for a risk was never strong to begin with,” Kabat said.
The IARC panel based its conclusions on case-control studies, which are performed by enrolling patients with a particular disease and comparing what they’ve been exposed to with the exposures of other patients who don’t have that disease. But these studies can be flawed, critics say, because subjects’ recollections can be incomplete or inaccurate. Early coffee studies focused on the bladder and kidney and didn’t find consistent results.
Alternatively, cohort studies, which follow a group of people over many years, overcome case-control problems because data is collected ahead of any diagnosed disease, including exposures.
In 1991, IARC concluded that evidence showed no link between coffee and breast cancer, according to the data summary it produced at the time. Evidence that coffee causes cancer in the pancreas, ovary or other sites was deemed inadequate. The same went for cancer in animal studies. But the agency found “limited evidence” that coffee consumption can cause cancer in the human bladder. So it determined coffee is possibly carcinogenic to the human urinary bladder.
IARC looked at two cohort studies and 26 case-control studies. The cohort studies did nothing to support an increased risk of cancer. The association between coffee and bladder cancer varied widely between case-control studies. In 16, there was a “weak positive association.” In seven, the association was “significant.” Another six showed no association.
“Taken as a whole, these data are consistent with a weak positive relationship between coffee consumption and the occurrence of bladder cancer, but the possibility that this is due to bias or confounding cannot be excluded,” the 1991 summary of data states.
Coffee exonerated; 'flimsy' studies put to rest
In June, IARC announced that its group of 23 scientists found no conclusive evidence that drinking coffee causes cancer. But very hot drinks might, they said. After reviewing 1,000 studies in humans and animals, the group concluded that there is “inadequate evidence for the carcinogenicity of coffee drinking overall.” Thus, it was deemed “not classifiable as a carcinogen” — a step down from its previous classification.
The coffee industry responded enthusiastically to the announcement.
“This is great news for coffee drinkers and confirms evidence from an avalanche of studies by highly respected and independent scientists,” National Coffee Association President Bill Murray said in a statement in June.
But the re-evaluations doesn’t go far enough, Kabat said, because despite strong evidentiary support, IARC placed coffee in the third group when it should be in the fourth.
“The main thing is that, given the large amount of new and much larger and better studies that have accumulated in the past 25 years, why would one say ‘not classifiable?’ This makes no sense,” he said. “It points (out) that IARC is willing to say there is a ‘possible’ risk based on very flimsy studies, but when there is much more evidence of a higher caliber that seems to point to the absence of a risk, IARC declares coffee ‘not classifiable.’”