Drinking large amounts of tea could increase the risk of prostate cancer, research has shown.
Scientists found that more than seven cups a day raised the chances of men developing the disease by 50%.
But whether the link is causal or due to coincidence is still unknown.
Study leader Dr Kashif Shafique, from the Institute of Health and Wellbeing at the University of Glasgow said: "Most previous research has shown either no relationship with prostate cancer for black tea or some preventive effect of green tea.
"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."
The Scottish researchers tracked the health of more than 6,000 men aged between 21 and 75, over a period of 37 years.
Participants provided information about their tea, coffee and alcohol consumption, smoking habits and general health.
Just under a quarter of the men were heavy tea drinkers. Of these, 6.4% developed prostate cancer during the course of the study.
Those drinking more than seven cups of tea a day were 50% more at risk than those who drank no tea or up to three cups.
The findings are reported in the journal Nutrition and Cancer.
Dr Shafique added: "We found that heavy tea drinkers were more likely not to be overweight, be non-alcohol drinkers and 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."
Each year almost 41,000 men in the UK are diagnosed with prostate cancer and around 11,000 die from the disease.
Men taking part in the study were drinking traditional black tea rather than green tea, which has been shown to have anti-cancer properties.
Black tea contains far fewer flavanols, protective plant chemicals, than green tea. But the researchers said they knew of no ingredient in black tea that might promote prostate cancer. Drinking large quantities of tea had no link to more aggressive forms of the disease.
The researchers concluded: "There has been much interest in the preventive effects of green tea on prostate cancer risk; however, we found a harmful effect of black tea on prostate cancer risk.
"The association between tea intake and prostate cancer should be investigated in prospective epidemiological studies in relation to different compositions of tea."
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