LONDON, U.K.
Hundreds of studies have demonstrated that tea is an effective adversary of cancer according to the UK Tea Council, suggesting a widely quoted research paper published by the University of Glasgow last week “is most likely an anomaly.”
“This new study is completely at odds with the rest of the literature on black tea and prostate cancer, where laboratory and human studies have tended to find that tea reduces prostate cancer risk,” said Dr. Carrie Ruxton, a dietician on the Tea Council’s Tea Advisory Panel.
The authors acknowledged this by claiming to be unaware of anything in black tea that would promote carcinogenic activity, said Ruxton.
Dr. Kashif Shafique, who led the research, said: “I was surprised when we discovered there does seem to be a link. We found that with each cup of tea drank above seven cups, the bigger the risk of you catching the cancer.
“We don't know whether tea itself is a risk factor or if tea drinkers are generally healthier and live to an older age when prostate cancer is more common anyway,” said Shafique. Researchers were “unaware of any constituent of black tea that may be responsible for carcinogenic activity in prostate cells,” he said.
The study of 6016 individuals between the ages of 21 and 75 began in 1970. Results published in the peer-reviewed science journal Nutrition and Cancer, do show a cause and effect relationship between tea drinking and cancer risk, according to Ruxton.
“Tea drinking is simply a marker for some other issue. That may be due to issues with stress, or perhaps diet,” she said. “The result is most likely to be an anomaly due to the observational nature of the study and the small number of tea consumers in the high category who developed prostate cancer (92, or 6% of ‘high’ consumers).”
Those drinking a moderate level of four to six cups of tea a day were not at any increased risk compared with those who drank the least.
Britain’s National Health Services blog NHS Choices reported that “despite its size and long duration, this study had many limitations that call into question the reliability of its results. Information on tea consumption and other lifestyle factors was only collected at the start of the study. Given the average follow-up was 28 years, it is unlikely that tea drinking habits, and other behaviours such as alcohol and smoking levels, remained stable over this entire period. This could have affected the results.”
NHS observed the heaviest tea drinkers also shared healthy behaviors, such as having a healthy weight, not drinking alcohol and having optimum cholesterol levels. “They raised the possibility that these men, who were generally healthier, may have lived for longer, allowing more time for prostate cancer to develop. As prostate cancer risk is known to increase with age, those living longer are more likely to develop the condition, which could explain this result,” according to NHS.
“Though this was a large study, only 318 men developed prostate cancer during the follow-up period,” according to the NHS. “If these men are further subdivided according to the amount of tea they drank, smaller sample sizes are created that can affect the reliability of risk estimates.”
NHS advised “the results of this study should not alarm male tea drinkers. However, men should remain alert to the signs and symptoms of prostate cancer regardless of their tea-drinking habits.”
Hundreds of studies have reported the beneficial impact of black tea on health, particularly heart health, due to its high polyphenol content, said Ruxton.
Until we know more, the British love affair with a nice cuppa can continue uninterrupted, said Tea Council spokesman Bill Gorman. “If you want to know more about the limitations of the study, read this great analysis of the research on NHS Choices.”
Sources: NHS Choices, UK Tea Council, The London Telegraph