Diabetic Benefits of Black Tea - Study
Tea Polysaccharides Help Control Blood Glucose Levels
Aug 18, 2009
Tea is the world’s second-most consumed drink after water, and already has a healthy reputation for antioxidants, boosting the immune system and lowering high blood pressure. A new study shows black tea may also help diabetics manage their glucose levels.
The study, published in the Institute of Food Studies journal, Journal of Food Science, looked at the chemicals, particularly polysaccharides, in green tea, oolong tea and black tea. Polysaccharides are a type of carbohydrate that includes starch and cellulose, which have been shown to retard the absorption of glucose.
“Many efforts have been made to search for effective glucose inhibitors from natural materials,” said lead researcher Dr Haixia Chen. “There is a potential for exploitation of black tea polysaccharide in managing diabetes.”
Diabetes mellitus, particularly Type 2 or late onset diabetes, is a major and rapidly increasing health problem all over the world, because of its chronic nature and disabling complications.
Controlling postprandial hyperglycemia (exaggerated rise in blood sugar following a meal) and inhibiting oxidative stress by increasing consumption of antioxidants are ways the patient can assist in the treatment of his diabetes.
Black Tea Known to Manage Diabetes in Asia
The hypoglycaemic (lowering blood glucose levels) effect of tea has been known for centuries in China and Japan, where tea is a remedy for diabetes.
This effect of tea’s polysaccharides has been studied scientifically in the past five years, but Dr Chen’s research is the first into its other action – glycosidase inhibition (inhibiting the uptake of glucose) from food recently eaten.
“Little is known about the glycosidase inhibitory effects of tea polysaccharides,” Dr Chen said. “The aim of this study was to find a tea polysaccharide with the best potential for exploitation in curing diabetes.”
The Search for Glucosidase Inhibitors in Tea
Dr Chen said glucosidase inhibitors are currently interesting to researchers “owing to their promising therapeutic potential in the treatment of disorders such as diabetes, HIV infection, metastatic cancer, and lysosomal storage diseases.
“Many studies have focused on the research for effective and safe α-glucosidase inhibitors from natural materials to develop a physiological functional food or lead compounds for use in anti-diabetes drugs,” he said
Black Tea Polysaccharides Best at Blocking Glucose
Dr Chen’s team at the Tianjin Key Laboratory in China tested three varieties of tea for their polysaccharide content: green, oolong and black. The tea samples were bought from the same local tea market, and had been produced by the same factory – the Huangshan Mountain Tea Factory, in Anhui, China
The researchers isolated the polysaccharide-rich fraction from powdered samples of green tea, oolong tea, and black tea, analyzed the chemical composition of each, and evaluated the glycosidase inhibitory effects and antioxidant activities of each of the three kinds of tea polysaccharides.
At the end of the process, Dr Chen and his team determined that the polysaccharides in black tea performed the best at inhibiting the uptake of glucose from recently eaten food.
Antioxidant Activities of Tea Polysaccharides
Oxidative stress is another contributor to chronic illnesses such as diabetes, cancer, rheumatoid arthritis, and atherosclerosis, as well as in aging.
It’s well known that tea, especially green tea, contains high levels of antioxidants that scavenge the cell-damaging oxygen-derived free radicals. Dr Chen’s team found that the polysaccharides in black tea outperformed even those in green tea in scavenging free radicals.
“The scavenging effects of green tea polysaccharides and black tea polysaccharide were more effective than those of oolong tea,” Dr Chen said. “Black tea polysaccharides showed the highest activity.”
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