Storm clouds are brewing in California's coffee cups. Companies across the state will have to add a cancer-warning label to coffee, a judge ruled last week, because the drink contains a chemical called acrylamide.
Los Angeles County Superior Court Judge Elihu M. Berle sided with a nonprofit organisation in a case against Starbucks, Peets and dozens of other coffee chains, saying that businesses that sold coffee were in violation of a state regulation called Proposition 65. Prop 65 requires businesses with at least 10 employees to disclose any carcinogens and toxic chemicals in their products.
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The lawsuit, filed by an organisation called the Council for Education and Research on Toxics, cites the presence of acrylamide in coffee. The International Agency for Research on Cancer, a branch of the World Health Organization, describes acrylamide as a human neurotoxin and a "group 2A probable carcinogen."
With those classifications, the chemical certainly does not sound like something people want floating in their morning pick-me-up. But experts said coffee drinkers should not change their habits on the basis of the new ruling.
"The name, 'acrylamide,' it makes it sound scary," said Michelle Francl, a chemist at Bryn Mawr College in Pennsylvania. But, she pointed out, a liquid labelled "oxidane" sounds ominous, even though that's a fancy term for water.
Rodents fed massive amounts of acrylamide do develop cancer. This is an "acceptable and appropriate" way to determine a carcinogenic effect, said J. Leonard Lichtenfeld, the American Cancer Society's deputy chief medical officer. But anything - including water and oxygen - can be unsafe at the wrong dosage. Those lab rats and mice were dosed at rates 1000 to 10,000 times higher than what humans consume in food, according to the American Cancer Society.
Links between cancer and acrylamide in humans are weak or need to be replicated in additional studies, said Timothy Rebbeck, a professor at the Dana-Farber Cancer Institute in Boston.
Lichtenfeld agreed. "There are no well-done human studies that answer the question definitively," he said. What research there is indicates that the human body does not absorb the chemical at the same rate as rodents do, and we also metabolise it differently.
"From a practical standpoint would we recommend people stop drinking coffee as a result of the judge's decision? No," Lichtenfeld said. "That's not what the science shows us."
Scientists at Stockholm University in Sweden discovered acrylamide in fried and baked foods in 2002. As starchy foods heat up, their sugars and amino acids react. Acrylamide is one of the byproducts.
"You can't really make roasted coffee without making acrylamide," Francl said. "What feels slightly chemophobic about it is to focus on coffee and not widely where acrylamide shows up."
When the Food and Drug Administration tested various foods for acrylamide, the highest levels were found in coffee, chocolate, bread, cereal and especially in french fries and potato chips. (But even in chips, the highest acrylamide concentrations were measured in thousands of parts per billion, much lower than the levels that cause cancer in lab animals.)
It is easy for health professionals to suggest laying off the fries and chips just in case acrylamide is dangerous. Coffee, however, has possible health benefits, muddying the picture.
In November, the British Medical Journal published an umbrella review - pooling 201 studies that in turn had pooled smaller studies - of coffee and health. Higher consumption of coffee was associated with a lower risk of prostate cancer, endometrial cancer, leukemia, melanoma and other specific cancers.
"There are lots of studies that suggest coffee is protective for cancer," Rebbeck said. "That evidence is at least as strong as the evidence against acrylamide."
In 2016, the International Agency for Research on Cancer concluded that coffee was "unclassifiable" as a human carcinogen.
"The reality is coffee is not carcinogenic, according to IARC," Lichtenfeld said.
Research into coffee consumption is difficult and often based on how people report their habits, which can be muddled by other foods they eat and their behaviours.
None of the protective associations between coffee and cancer are definitive, Rebbeck cautioned. (If they were, oncologists might be recommending infusions of coffee.) The science of coffee is too nuanced to present on a warning label, he said. "People can't do a meta-analysis of the data while they're in the supermarket."
It is possible to "overload people with messages about risks and harms that are not particularly relevant," Lichtenfeld said.