Now before you start ordering that second steaming cup, it's important to know that the WHO report wasn't all good news. There was another significant finding: “Very hot” beverages “probably” cause cancer. This is mostly based on studies related to the consumption of a traditional drink called mate or cimarrón in South America, where the tea can be taken at temperatures around 158 degrees Fahrenheit (or 70 degrees Celsius). That's significantly hotter than people in North America or Europe usually consume their drinks.
The findings were published in the Lancet Oncology on Wednesday.
“These results suggest that drinking very hot beverages is one probable cause of esophageal cancer, and that it is the temperature, rather than the drinks themselves, that appears to be responsible,” said Christopher Wild, director of the International Agency for Research on Cancer.
In a conference call with reporters, officials were unable to quantify the risk — “We can’t put a number on it at this stage,” they said — but said that it appears that the higher the temperature of the drink the higher the risk.
They also had some practical advice for people who consume hot beverages.
“Certainly wait a few minutes more before drinking your drink,” the IARC said.
Mariana Stern, one of 23 scientists from 10 countries who was part of the committee that made the determination, explained in an interview that while we don’t understand the mechanisms behind why hot drinks may lead to cancer, there is some evidence that they may damage the cells in the esophagus or cause them to go out of control. She said the WHO’s new thinking on hot beverages should be taken seriously and people should become more educated about the temperatures of various liquids they ingest.
“What is very hot for you is not very hot for me. So it’s important for people to become familiar with what temperatures of the things they are drinking really are,” said Stern, an associate professor of preventive medicine at the University of Southern California.
The average temperature for coffee consumption in the United States is about 140 degrees Fahrenheit, but some restaurants will serve it at higher temperatures. The famous lawsuit against McDonald’s by a customer who said she suffered third-degree burns after spilling coffee on herself involved coffee at temperatures of 180 to 190 degrees. Water boils at 212 degrees. Lukewarm water is about 105 degrees. Many coffee makers keep temperature at around 160 degrees or higher.
You might also consider taking your beverages cold or iced. The same studies on mate were inconclusive in terms of the cancer link when the beverage was not very hot.
The decision to reclassify coffee is a major victory for the industry, which has been aggressively lobbying for such an action. For organizations, such as the WHO, that are charged with protecting the public’s health, it’s often politically trickier to say a product causes no harm than to say a product causes harm — even for one as beloved as coffee. In the United States, when a federal advisory committee issued recommendations regarding the Dietary Guidelines for Americans in 2015 and said coffee could be part of a “healthy diet,” there was a significant backlash. The new U.S. recommendations, officially issued in January, say that up to five eight-ounce cups a day is fine.
The National Coffee Association cheered the WHO finding, pointing out that it's the first time a foodstuff or beverage has ever been positively reclassified by the scientists.
“Coffee drinkers have known for a long time that their go-to beverage is a super food,” the association's president, Bill Murray, said in a statement. “Today we can brew or buy a cup with even more confidence thanks to science.”
“More confidence” are the key words here as science is a moving target, especially in terms of food, as bodies making recommendations about what people consume have tended to flip-flop in recent years.
The original determination that coffee may be linked with cancer, made in 1991, came from a limited number of studies on bladder cancer.
The WHO working group said its new classification was based on a review of more than 1,000 studies in humans and animals. They said there was “inadequate evidence” for the carcinogenicity of coffee drinking overall. It noted that epidemiological studies mentioned no impact of coffee drinking, specifically on cancers of the pancreas, prostate and female breast. Reduced risks were seen for cancers of the liver and uterine endometrium. For more than 20 other types of cancer, the evidence was inconclusive.
Scientists now believe that tobacco smoking, which is correlated with heavy coffee drinking, may be to blame.
Although the WHO’s coffee decision was carefully thought out and involved countless hours of research by some of the top minds in nutrition science, you should keep in mind that it’s just a snapshot in time in terms of what we know. Remember that meat was once thought to be good and important for your health, but the WHO told us last year that it now thinks hot dogs and bacon cause cancer and red meat “probably does,” too. Many other changes have taken place over just the past few months: Cholesterol, the boogieman of our diets since the 1960s, suddenly became less harmful in January when the new Dietary Guidelines for Americans came out — as did salt.
The coffee issue is also far from definitively resolved. Early work shows that there may be at least one location in your genes that may determine whether you process caffeine quickly or slowly and that there is a roughly 50-50 split among humans. That has led some experts to wonder whether a general rule about the good or ill effects of a food means anything to individuals.
“A one-size-fits-all recommendation for coffee won’t work. Some people just can’t tolerate it,” Marilyn Cornelis, a Northwestern medical school professor, told The Washington Post earlier this year.
This post has been updated.