A new study linking consumption of a daily cup of hot tea with reducing the risk of developing glaucoma is creating a stir.
For their study, researchers from the University of California, Los Angeles and Brown University in Providence, Rhode Island analyzed data from the National Health and Nutrition Examination Survey (NHANES), a large study on the health and nutritional standing of adults in the United States since the 1960s.
The aim of the study was to consider the link between consumption of caffeine and decaffeinated beverages—coffee, tea and soft drinks—and glaucoma. Among 1,678 NHANES survey participants, about 5% had been diagnosed with glaucoma.
The findings of the study, "Frequency of a diagnosis of glaucoma in individuals who consume coffee, tea and/or soft drinks," were published online Dec. 14 in the British Journal of Ophthalmology.
Though no statistically significant link was found between developing glaucoma and consuming coffee, iced tea, decaffeinated hot tea and soft drinks, participants who consumed at least one cup of hot tea daily had 74% decreased odds of having glaucoma, compared to those who didn't drink it.
Health benefits of drinking tea
Glaucoma is a group of eye disorders that lead to progressive damage to the optic nerve, a bundle of about 1 million individual nerve fibers that transmits visual signals from the eye to the brain. People with glaucoma can lose nerve tissue, resulting in vision loss.
The Centers for Disease Control and Prevention estimate that about 3 million Americans have glaucoma—the second leading cause of blindness in the world. At high risk for the disease are people over 60 years of age, African American over 40, people with diabetes and people with a family history of glaucoma.
Susan Summerton, O.D., is a certified nutrition specialist with the Ocular Wellness and Nutrition Society who practices in Florida. Dr. Summerton has written about the benefits of tea to overall health—citing increased intake of tea's disease-fighting plant compounds such as flavonoids.
"Studies like this remind doctors of optometry and patients that what we eat or drink can have an impact on health," Dr. Summerton says. "Tea is a major source of flavonoids and L-theanine (amino acid found in green and black teas). Flavonoids from tea leaves have similar benefits as the phytochemicals found in fruits and vegetables. Plant-nutrient flavonoids are powerful antioxidants with anti-inflammatory and immune system benefits.
"The antioxidant properties in tea have potential value in glaucoma," she says. "There is increasing evidence that both an activation of glial cells and oxidative stress in the axons play an important role. Dietary flavonoids and tea consumption have been described to improve endothelial function and flow-mediated dilation via effects with nitric oxide. Improving the unstable ocular blood flow in glaucoma may also help reduce the oxidative stress."
L-theanine has been linked in studies to health benefits. Previous research has indicated it has neuroprotective benefits, including blocking the binding of L-glutamic acid to glutamate receptors in the brain, as well as positive effects on blood pressure and cardiovascular protection, Dr. Summerton says.
In a double-blind, randomized study in which hypertensive men drank one cup of black tea daily, both systolic and diastolic blood pressure were reduced," she says. "There is speculation that a healthier blood vessel lining would help your organs including your eye receiving more blood, oxygen and, nutrients."
The new study opens the door for more research, Dr. Summerton says. Though the study established an association, it did not demonstrate a cause and effect.
"If a simple action like drinking tea can protect against potential health problems, whether you have glaucoma risk or not, perhaps a cup a day is a valid health recommendation," she says. "However, it is not a reason to discontinue any prescribed glaucoma treatment."
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