Men who drink lots of tea are far more likely to develop prostate cancer, a new study has revealed.
Researchers found that those who drank seven or more cups a day had a 50 per cent higher risk of contracting the disease than those who had three or fewer.
The warning comes after scientists at the University of Glasgow tracked the health of more than 6,000 men for four decades.
Their findings run counter to previous research, which had suggested that tea-drinking lowers the risk of cancer, as well as heart disease, diabetes and Parkinson's disease.
The study, led by Dr Kashif Shafique, began in 1970.
Participants aged between 21 and 75 were asked to complete a questionnaire about their usual consumption of tea, coffee and alcohol as well as their smoking habits and general health, and had to attend a screening examination.
Just under a quarter of the 6,016 men were heavy tea drinkers, consuming seven or more cups a day. Of these, 6.4 per cent developed prostate cancer over the next 37 years.
Researchers found that the subjects who drank the most tea were often teetotalers and led healthy lifestyles.
As a result, they may have been at a lower risk of death from "competing causes," effectively giving them more time to develop prostate cancer, the study revealed.
"Most previous research has shown either no relationship with prostate cancer for black tea, or some preventive effect of green tea," the Daily Mail quoted Dr Shafique as saying.
"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," he said.
He added that those drinking the most tea were less likely to be overweight or drink alcohol, and more likely to have healthy cholesterol levels.
"However, we did adjust for these differences in our analysis and still found that men who drank the most tea were at greater risk of prostate cancer," he said.
Dr Shafique did stress, however, that his team was "unaware of any constituent of black tea that may be responsible for carcinogenic activity in prostate cells."
Previous research has found health benefits from flavonoids - antioxidant compounds in tea that are thought to control inflammation, reduce excess blood clotting and limit narrowing of the arteries.
Of seven previous studies on black tea and prostate cancer, four found a potentially protective effect while the remainder found no effect either way.
"Whilst it does appear that those who drank seven or more cups of tea each day had an increased risk of developing prostate cancer, this did not take into consideration family history or any other dietary elements other than tea, coffee and alcohol intake," Dr Kate Holmes, head of research at The Prostate Cancer Charity, said.
"It is therefore unclear as to whether there were other factors in play which may have had a greater impact on risk," she added.
Almost 80 per cent of Britons drink tea, consuming an estimated 165 million cups each day. The British tea industry is thought to be worth more than 700-million-pounds a year.
Prostate cancer strikes 40,000 British men each year, causing more than 10,000 deaths.
The study was published in the journal Nutrition and Cancer.