Drinking a cup of hot tea at least once a day may significantly lower risk of developing glaucoma – a serious eye condition, a study suggests.
However, drinking decaffeinated and caffeinated coffee, decaffeinated tea, iced tea and soft drinks does not seem to make any difference to glaucoma risk, said researchers from the University of California in the US.
Glaucoma causes fluid pressure to build up inside the eye (intraocular pressure), damaging the optic nerve.
It is one of the leading causes of blindness worldwide, and currently affects 57.5 million people, and is expected to increase to 65.5 million by 2020, according to the study published in the journal BMJ.
Previous research suggests that caffeine can alter intraocular pressure, but no study so far has compared the potential impact of decaffeinated and caffeinated drinks on glaucoma risk.
The researchers looked at data from the 2005-2006 National Health and Nutrition Examination Survey (NHANES) in the US.
Among the 1678 participants who had full eye test results, including photos, 84 (5 per cent) adults had developed the condition.
They were asked how often and how much they had drunk of caffeinated and decaffeinated drinks, including soft drinks and iced tea, over the preceding 12 months, using a questionnaire.
Compared with those who did not drink hot tea every day, those who did, had a lower glaucoma risk, the data showed.
After taking account of potentially influential factors, such as diabetes and smoking, hot tea-drinkers were 74 per cent less likely to have glaucoma.
However, no such associations were found for coffee – caffeinated or decaffeinated – decaffeinated tea, iced tea or soft drinks.