Glaucoma causes the buildup of pressure inside the eye (intraocular pressure) and damages the optic nerve. It is one of the leading causes of blindness worldwide and currently affects 57.5 million people, although it is expected to increase to 65.5 million by 2020. Previous research suggests that caffeine can alter intraocular pressure, but no study has so far compared the potential impact of decaffeinated and caffeinated beverages on the risk of glaucoma, reports Europa Press.
Then, a team of researchers analyzed data from the National Health and Nutrition Survey (NHANES, for its acronym in English) 2005-2006 in the United States. This is a nationally representative annual survey of about 10,000 people that includes interviews, physical exams and blood samples, designed to measure the health and nutritional status of American adults and children.
In this particular year, eye exams for glaucoma were also included. Among the 1,678 participants who obtained full results from the eye test, including photos, 84 adults (5 percent) developed the condition. They were asked how often and how much they had taken caffeinated and decaffeinated beverages, including soft drinks and iced tea, in the last 12 months, using a validated questionnaire.
Compared to those who did not drink hot tea every day, those who did had a lower risk of glaucoma, according to the data. After taking into account potentially influential factors, such as diabetes and smoking, hot tea drinkers were 74 percent less likely to have glaucoma. But these associations were not found for decaffeinated, caffeinated or decaffeinated coffee, iced tea or soft drinks.
This is an observational study so no firm conclusions can be drawn about cause and effect, and the absolute numbers of those with glaucoma were small. Information about when glaucoma had been diagnosed was also not available. The survey also did not ask about factors such as the size of the cup, the type of tea or the duration of the brewing time, which may have been influential.
But tea contains antioxidants and anti-inflammatory and neuroprotective chemicals, which have been associated with a lower risk of serious conditions, which include heart disease, cancer and diabetes, according to scientists. Previous research suggested that oxidation and neurodegeneration may be involved in the development of glaucoma and conclude: “More research is needed to establish the importance of these findings and whether the consumption of hot tea may play a role in the prevention of glaucoma.”.