Tea is not only the most popular beverage in the world, it’s also good for you. Over the past 20 years, scientists have discovered potential benefits from tea against cancer, high blood pressure and infection. Now comes a report that tea may be an effective weapon in the fight against diabetes.
First, some basic tea facts:
Tea is what you get when you pour boiling water over the leaves of the tea plant, Camellia sinensis, an evergreen shrub native to Southeast Asia.
According to legend, the Chinese emperor Shen-Nung learned how to brew tea in 2737 BC when a few leaves from the plant accidentally fell into water he was boiling. Tea eventually spread from China to Japan (taken by Buddhist monks), and from thence to Java, the Dutch East Indies, and other tropical and subtropical areas. British merchants formed the East India Company in 1600 and introduced tea to England and the American colonies.
Tea plants are grown in areas that have lots of rainfall and rich, loamy soil. Although nowadays the plants are frequently cloned, traditionally, tea-plant seeds are planted in a nursery and replanted when they’re between six and 18 months old. The plants are kept pruned to a height of about one metre, which encourages the growth of new leaves. It takes 2 1/2 to five years, depending on the altitude (the higher the altitude, the slower the plant grows but the better the tea tastes), for the plant to produce commercially valuable leaves.
Tea is harvested by hand, several times a year. The crop of newly sprouted leaves and buds is plucked and taken to a factory for processing into black, oolong or green tea.
To make black tea, the leaves are spread out and partially dried for most of a day, then rolled in a machine that bruises and breaks them, releasing an enzyme that gives the tea its flavour and aroma. Next, the lumps of tea are broken and spread in a fermentation room to oxidize, where they turn a copper colour. Then the leaves are fired with hot air, which stops the fermentation process and dries the leaves, turning them black. Then they’re sifted, sorted, and graded.
Oolong tea is made much like black tea, except the leaf ferments for a shorter period, so that when it’s dried, the edges turn coppery and the centre remains green.
Green tea, favored in China and Japan, is steamed right after harvest to destroy the enzyme released in other teas when the leaves are broken. This prevents fermentation and means that the tea doesn’t even smell like black tea. Then the leaves are rolled, which removes moisture and gives them a characteristic curl, and dried.
Teas are graded by size rather than quality. The smallest leaves and buds make up the top grades, called Pekoe (and pronounced PECK-o) and bottom grades are leaf fragments and “dust.” About 80 percent of the crop winds up in the lowest grades.
Tea has long been drunk as a folk remedy for diabetes in China, the West Indies and central Africa; apparently with good reason.
Richard Anderson, a biochemist at the United States Department of Agriculture’s Beltsville Human Nutrition Research Center in Maryland, and his colleague Marilyn Polansky, analyzed several herbs, spices and plants for insulin benefits. To do so, they grew fat cells from rats (fat cells are highly sensitive to insulin) in test tubes, then gave the cells mildly radioactive sugar (so it could be easily tracked), insulin, and various plant extracts. The more the extracts aided insulin activity, the more sugar the cells would convert into energy.
The scientists found tea (black, green or oolong, caffeinated or decaffeinated, it didn’t matter) boosted insulin activity more than any other substance they tested, thanks to the presence of a chemical in tea called epigallocatechin gallate.
Adding whole or skim milk, non-dairy creamers or soy milk to tea inhibited the insulin boost. Lemon juice, on the other hand, didn’t.
Tea’s insulin-boosting compounds cleared from the cells quite quickly, some in less than six hours and some in less than four, so if the benefit holds true in humans, it would take regular tea-drinking to see any long-term benefit. The next step, of course, is to carry out studies to see if the insulin boost does occur in living humans, as opposed to test-tubed rat fat.
Considering how many people like tea, researchers should have no shortage of volunteers.
