Drinking very hot tea appears to increase the risk of oesophageal cancer, a new study has shown, prompting suggestions for a four-minute wait before swallows of freshly boiled tea.
The study from northern Iran, the largest so far to explore tea-drinking habits and oesophageal cancer, has corroborated earlier research from India, Singapore and South America that linked this cancer to hot beverages.
Researchers from the Tehran University of Medical Sciences studied tea-drinking habits and patterns of oesophageal cancer in Golestan province where black tea is popular. They found that people who consumed very hot tea (defined as 70°C or higher) had an eight-fold higher risk of oesophageal cancer than people who drank tepid tea (65°C or lower).
They found that drinking tea at temperatures between 65°C and 69°C — defined as simply hot — was associated with twice the risk of cancer of the oesophagus. Their research will appear in the British Medical Journal on Friday.
“It’s clear hot beverages are contributing to high levels of oesophageal cancer in this population, Paul Brennan, a research team member from the International Agency for Research in Cancer in Lyons, France, told The Telegraph.
“But other factors may be associated with oesophageal cancer in other populations,” said Brennan, head of genetic epidemiology unit at the IARC. “We need to investigate different factors in different regions or populations.”
The Iranian study also showed that waiting for tea to cool lowered the risk of the cancer. People who typically drank their tea within two minutes after it was poured had a five-fold higher risk than those who waited for four minutes or longer.
Although previous studies have pointed to the potential danger of hot beverages, Iranian digestive disorder specialist Reza Malekzadeh and his colleagues are among the first to investigate the link through rigorous temperature measurements.
Malekzadeh said the significance of the new research was in the use of statistical techniques to eliminate the effects of other risk factors that could also contribute to oesophageal cancer.
But doctors assert that there is no cause for alarm. “The public health message here is that people should wait four minutes before they begin sipping from a cup of hot tea,” Malekzadeh told The Telegraph.
Eight years ago, Rup Kumar Phukan and his colleagues at the Regional Medical Research Centre, Dibrugarh, Assam, had examined dietary habits in parts of northeastern India and shown that hot beverages and spicy food were linked to oesophageal cancer.
They had suggested that the long-term consumption of exceptionally hot food or beverages could cause chronic irritation and harm the lining of the oesophagus. “But chewing tobacco and smoking are also likely to be among the contributing factors in this region,” said a scientist at the Dibrugarh centre.
The Iranian study measured tea temperatures consumed by more than 48,500 people and studied tea-drinking habits of 300 patients with oesophageal cancer and 571 healthy people, emerging as the largest study on the topic.
Speculating on mechanisms to explain the link, the researchers have pointed out that chronic inflammation by high temperatures may stimulate the release of nitric oxide and reactive oxygen species — potentially harmful biomolecules.
Doctors caution that cancer is almost always a multi-factorial disease. The risk may be lowered or increased by several factors. Low consumption of fruits and vegetables, for instance, may increase the risk of cancer.
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Sources: The Telegraph (Kolkata, India)