Coffee Not a Carcinogen, But May Still Be Too Hot to Handle

Coffee lovers can breathe a sigh of relief. Though coffee was on the list of possible carcinogens for two and a half decades, the International Agency for Research on Cancer (IARC) announced June 15 that there is no conclusive evidence to warrant alarm.

In 1991, the IARC, the cancer-specialty arm of the World Health Organization (WHO), gave coffee a Group 2B carcinogen classification, meaning the substance is “possibly carcinogenic to humans.” But in May 2016, a working group of 23 scientists from 10 countries reviewed nearly 500 relevant epidemiological studies and determined that coffee had no carcinogenic effect for pancreatic, female breast and prostate cancers. The risk was reduced for liver and uterine endometrium cancers, and evidence was inadequate for any conclusion to be drawn for more than 20 other cancers.

A summary of the findings was published in The Lancet Oncology and Volume 116 of the IARC Monographs will have a detailed assessment of the analysis.

“The [original] classification as possibly carcinogenic in 1991 was based on indication of increased risk of bladder cancer among coffee drinkers that were seen in many case-control studies of hospital patients,” Dana Loomis, deputy head of the Monographs Section of the IARC said in an interview with CURE. “There are now many more studies available and their quality has improved.”

But that piping hot cup of joe is not completely in the clear just yet. While coffee itself might not cause cancer, the temperature might. The IARC found that drinking beverages hotter than 149° Fahrenheit — including coffee and tea — correlates with esophageal cancer. “Very hot” beverages were designated a Group 2A carcinogen, meaning that they are “probably carcinogenic to humans.”

Studies from China, Iran, Turkey and South America, where maté is normally consumed at very high temperatures, found that the risk of developing esophageal cancer increased as the beverage got hotter.

“These results suggest that drinking very hot beverages is one probably cause of esophageal cancer and that it is the temperature, rather than the drinks themselves, that appears to be responsible [for causing cancer],” Loomis said.

But the findings were backed by limited evidence, meaning “positive association has been observed between exposure to the agent and cancer, but that chance, bias or confounding [factors] could not be ruled out,” Loomis explained.

The possibility of coffee preventing cancer has also been hard to pin down definitively. Though numerous studies have shown frequent coffee intake could decrease risk of colorectal, liver and endometrial cancers, Loomis said more research is needed.

“Although there are indications that it might have beneficial effects, it is too early to conclude that drinking coffee can prevent cancer,” Loomis said.