Insulin problems lie at the root of the potentially fatal illness diabetes, so researchers hope tea-based treatments will help treat or prevent the disease, which affects 17 million Americans. Not only that, this insulin-boosting phenomenon may explain why tea can help fight heart disease and high blood pressure as well.
"This is just one of the many well-established benefits that tea may have," researcher Richard Anderson, a biochemist at the USDA's Beltsville Human Nutrition Research Center in Maryland, told United Press International.
Tea has a long history as a folk remedy for diabetes in China, the West Indies and central Africa. Over the past 20 years scientists also have uncovered potential benefits from tea against cancer, high blood pressure and infection.
"Tea wasn't the only factor we looked at, but it was the best," Anderson said.
Anderson and his colleague Marilyn Polansky analyzed a host of herbs, spices and plants for any beneficial effect involving insulin, the hormone the body needs to convert sugar into energy. They took fat cells from rats and grew them in test tubes because fat cells are highly sensitive to insulin, Anderson explained. Then, they gave the cells mildly radioactive sugar, insulin, and various tea extracts. The radioactive sugar is easy to track and the more the extracts aided insulin activity, the more sugar the cells would convert.
The scientists found black, green and oolong teas boosted insulin activity the most. This insulin-augmenting effect was seen with both caffeinated and non-caffeinated teas, but not with herbal teas, which do not use leaves from tea bushes.
They also identified tea's most insulin-enhancing chemical, called epigallocatechin gallate. Adding whole or skim milk, nondairy creamers or soy milk appears to soak up tea's insulin-augmenting compounds and inhibit the insulin boost, although these milky sponges may release the tea extracts in the stomach, Anderson said. No absorption problem was seen with lemon juice.
"Hopefully people can get better simply by drinking tea," Anderson said. "These compounds clear from the body quite quickly, some in less than six hours, some less than four. The effects are not going to be that large, so you're going to need to continue drinking tea."
Anderson said his team also found cinnamon showed similar insulin-enhancing power. He suggests tea and cinnamon affects the cell proteins insulin binds to.
Diabetes is a disease where the body either does not make insulin or does not properly use it when it does produce it. The scientists think tea increases the body's sensitivity to insulin by setting off a chain reaction. As a result, the body attaches chemicals to insulin-binding proteins that enhance their activity.
Tea's insulin-boosting activity also might explain why tea seems to help prevent heart disease and high blood pressure, Anderson said. Medical investigators think high blood sugar damages blood vessels, and increasing insulin activity lowers blood sugar levels.
"This work seems to be truly new and extremely exciting," biochemist Anne-Marie Roussel at the Université Joseph Fourier in Grenoble, France, told UPI. "This work is well done, and the data is promising not only to treat diabetes but perhaps also in preventing it." Roussel and Anderson added more tea studies need to be conducted with patients, not in lab models.
The scientists described their findings in a report published online by the Journal of Agricultural and Food Chemistry.
(Reported by Charles Choi, UPI Science News, in New York)