According to a small study published online yesterday in the British Journal of Ophthalmology, drinking at least one cup of hot tea daily may be associated with a considerably lower risk of contracting glaucoma, a serious eye condition.
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However, drinking caffeinated and decaffeinated coffee, iced tea, decaffeinated tea, as well as soft drinks, is not found to create any difference to glaucoma risk.
Glaucoma damages the optic nerve by building up fluid pressure inside the eye. The condition currently affects 57.5 million people across the world, making it a leading cause for blindness worldwide. It is estimated that, by 2020, the number of people affected by glaucoma may increase to 65.5 million.
Although prior research indicated that caffeine has the ability to alter intraocular pressure, a study comparing the possible impact of caffeinated and decaffeinated drinks on glaucoma risk has yet to be carried out.
The current study analyzed data from the 2005-06 National Health and Nutrition Examination Survey (NHANES) in the US, a nationally representative annual survey that enrolled nearly 10, 000 people. It included interviews, physical examinations, and blood samples, designed to measure the health and nutritional status of US adults and children.
The 2005-06 NHANES also included eye tests for glaucoma for 1678 participants, among whom 5% (84 adults) were identified with the condition. Using a validated questionnaire—Food Frequency—the participants were asked how often and how much they had drunk caffeinated and decaffeinated drinks, including soft drinks and iced tea, over the preceding 12 months.
The data indicated that those who drank hot tea daily had a lower glaucoma risk than those who did not. After accounting for potentially influential factors, like smoking and diabetes, hot tea drinkers were 74% less probable to have glaucoma.
For coffee,-caffeinated and decaffeinated-decaffeinated tea, iced tea and other soft drinks, no such associations were found.
As the study was observational, firm conclusions on the cause and effect cannot be drawn. The study also has many limitations, like the small number of participants with glaucoma, lack of data on when glaucoma had been diagnosed, and lack of data on a few potentially influential factors such as cup size, tea type, or the length of brewing time.
However, according to the researchers, tea contains antioxidants as well as anti-inflammatory and neuroprotective chemicals, which are linked with a decreased risk of serious conditions like heart disease, cancer, and diabetes. Former research had suggested oxidation and neurodegeneration could be involved in glaucoma development.
"Further research is needed to establish the importance of these findings and whether hot tea consumption may play a role in the prevention of glaucoma," said the researchers.