WHO: Coffee not carcinogenic, but 'very hot' drinks may be

A large review of studies by the agency found coffee is not only not carcinogenic, but may actually have protective effects against some forms of cancer.

By Stephen Feller

After 25 years of suggesting coffee may be carcinogenic, researchers at the World Health Organization say the beverage may have anti-cancer effects for some forms of the disease. The agency says, however, that very hot drinks -- coffee, tea and even plain water heated beyond 150 degrees Fahrenheit -- may be carcinogenic. Photo by Dima Sobko/Shutterstock

Doubling back on decades-old warnings that consumption of coffee can increase risk for cancer, international researchers say the increased risk comes from drinking very hot beverages -- which can include coffee, but is not limited to the drink.

The International Agency for Research on Cancer says in a new report that beverages 150 degrees Fahrenheit or hotter increase risk for esophageal cancer, including coffee and tea.

In a 1991 report, the IARC, a part of the World Health Organization of the United Nations, deemed overconsumption of coffee as possibly carinogenic, a finding the agency stuck to even as other health organizations revised their own theories on the effects of coffee on cancer.

Green tea, on the other hand, has been shown in previous studies to contain levels of antioxidants, which may limit damage to cells and tissues that can lead to the development of cancer. The new findings on beverage temperature may suggest caution to those drinking tea for its anti-cancer potential.

"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," Dr. Christopher Wild, director of the IARC, said in a press release.

For the review, published in The Lancet, the IARC asked 23 researchers to review more than 1,000 studies in humans and animals on consumption of coffee, finding "inadequate evidence" that drinking coffee is carcinogenic.

Specifically, they found no evidence coffee has carcinogenic effects on pancreas, female breast, bladder or prostate cancer, and that "reduced risks" were seen for cancers of the liver and uterine endometrium. For more than 20 other cancers, the evidence was considered inconclusive.

The shift in warning is significant because coffee is the most consumed beverage in the United States, and global consumption has grown continuously by 2.5 percent per year since 2011, according to the Wall Street Journal.

While they note a higher rate of cancer in male coffee drinkers was seen, the researchers surmise men who drink the beverage were more likely to be smokers or exposed to chemical carcinogens than those who do not drink it.

Studies on very hot beverages in China, the Middle East and South America, as well as a South American drink called Mate, which is also consumed as piping hot as coffee, showed increased risk for esophageal cancer -- leading to the agency's suggesting that beverages above 150 degrees Fahrenheit are "probably carcinogenic to humans," including super hot plain water.