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However, drinking decaffeinated and caffeinated coffee, decaffeinated tea, iced tea and soft drinks do 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.
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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 percent less likely to have glaucoma.
However, no such associations were found for coffee – caffeinated or decaffeinated – decaffeinated tea, iced tea or soft drinks.