An international working group of scientists convened by the World Health Organization (WHO) has concluded that coffee should no longer be considered a carcinogen, although it found limited evidence that drinking very hot beverages can cause oesophageal cancer.
A summary of the final evaluations by the working group – which was convened by the International Agency for Research on Cancer, the cancer agency of WHO – was published today in The Lancet Oncology, and focused on the carcinogenicity of drinking coffee, maté and very hot beverages.
“These results suggest that drinking very hot beverages is one probable cause of oesophageal cancer and that it is the temperature, rather than the drinks themselves, that appears to be responsible,” said Dr. Christopher Wild, Director of the International Agency for Research on Cancer.
The working group found no conclusive evidence for a carcinogenic effect of drinking coffee. However, the experts did find that drinking very hot beverages probably causes cancer of the oesophagus in humans. No conclusive evidence was found for drinking maté at temperatures that are not very hot.
Specifically, drinking very hot beverages was classified as probably carcinogenic to humans. This was based on limited evidence from epidemiological studies that showed positive associations between cancer of the oesophagus and drinking very hot beverages.
Studies in places such as China, Iran, Turkey and South America, where tea or maté is traditionally drunk very hot (at about 70 °C), found that the risk of oesophageal cancer increased with the temperature at which the beverage was drunk.
In experiments involving animals, there was also limited evidence for the carcinogenicity of very hot water.
“Smoking and alcohol drinking are major causes of oesophageal cancer, particularly in many high-income countries,” Dr. Wild emphasized. “However, the majority of oesophageal cancers occur in parts of Asia, South America, and East Africa, where regularly drinking very hot beverages is common and where the reasons for the high incidence of this cancer are not as well understood.”
Oesophageal cancer is the eighth most common cause of cancer worldwide and one of the main causes of cancer death, with approximately 400,000 deaths – or five per cent of all cancer deaths – recorded in 2012. The proportion of oesophageal cancer cases that may be linked to drinking very hot beverages is not known. The working group also found that cold maté did not have carcinogenic effects in experiments on animals or in epidemiological studies. Therefore, drinking maté at temperatures that are not very hot was not classifiable as to its carcinogenicity to humans.
That finding was based on inadequate evidence in humans for the carcinogenicity of drinking cold or warm maté and inadequate evidence in experimental animals for the carcinogenicity of cold maté as a drinking liquid.
In addition, the group found that drinking coffee was not classifiable as to its carcinogenicity to humans. The large body of evidence currently available led to the re-evaluation of the carcinogenicity of coffee drinking, previously classified as possibly carcinogenic to humans by International Agency for Research on Cancer in 1991.
After reviewing more than 1,000 studies in humans and animals, the working group found that there was inadequate evidence for the carcinogenicity of coffee drinking overall. Many epidemiological studies showed that coffee drinking had no carcinogenic effects for cancers of the pancreas, female breast and prostate, and reduced risks were seen for cancers of the liver and uterine endometrium.
For more than 20 other cancers, the evidence was inconclusive, according to the working group.
The working group’s evaluation is in line with the WHO Technical Report Series 916 on Diet, Nutrition and the Prevention of Chronic Diseases, which states that people should not consume drinks when they are at a scalding hot temperature.