A new study has found inadequate evidence linking coffee to any cancer-causing effects - or carcinogenicity.

An international group of 23 scientists was convened by the International Agency for Research on Cancer (IARC), the cancer agency of the World Health Organisation (WHO).

It found "no conclusive evidence for a carcinogenic effect of drinking coffee."

The large body of evidence available has led to a re-evaluation of coffee drinking, which was previously classified as "possibly carcinogenic" to humans by the IARC in 1991.

"After thoroughly reviewing more than 1000 studies in humans and animals, the working group found that there was inadequate evidence for the carcinogenicity of coffee drinking overall", the IARC said.

It adds that many 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.

However, experts did find that drinking very hot beverages "probably" causes cancer of the oesophagus in humans.

"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," says IARC director Dr Christopher Wild.

Risk of oesophageal cancer

Drinking very hot beverages was classified as "probably" carcinogenic to humans, based on limited evidence from studies.

Studies in places such as China, Iran, Turkey, and South America - where tea or maté is traditionally drunk at about 70°C - found that the risk of oesophageal cancer increased with the temperature of the beverage.

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 said.

"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 recorded in 2012 - or 5% of all cancer deaths.

The proportion of oesophageal cancer cases that may be linked to drinking very hot beverages is not known.