When it comes to tea, the British may be on to something. Several recent studies suggest that chemicals in tea may help reduce the risk of several chronic diseases such as cancer, diabetes, and cardiovascular disease (CVD). These flavonoids also appear to support bone health in postmenopausal women.
There are many types of tea. White, oolong, green, and black teas all come from a plant called Camellia sinensis, but are processed differently to achieve different levels of oxidation. White tea has undergone minimal oxidation and black tea has undergone maximum oxidation. When green tea is fermented to make black tea, the reaction causes the simple flavonoids found in green tea, called catechins, to form more complex flavonoids, called theaflavins and thearubigins.
“In the process of making black tea, the green tea leaves are crushed up and undergo a chemical reaction, so the tea develops that orange color and flavor characteristic of black tea,” Joshua Lambert, an assistant professor in the department of food science at Pennsylvania State University tells TheDoctor. That orange color is indicative of the formation of theaflavins.
You should think of tea as a plant food, says Jeffrey Blumberg, a professor of nutrition science and policy at Tufts University. It is just like other plant foods, such as fruits and vegetables, and whole grains that we are so often told to eat. Not only do plant foods contain vitamins, minerals, and fiber, they also contain phytochemicals, such as flavonoids, which belong to a class of phytochemicals called polyphenols.
Drinking tea is a little like having a serving of fruits and vegetables. All teas from C. sinensis naturally contain between 100 to 300 mg of flavonoids per serving when prepared at about 1.0 gram of tea per 200 mL water (about 6.8 ounces), says Blumberg. “The simple bottom line is that tea is a healthy beverage, and that you should choose it more often, or at least start to drink some if you don’t,” Blumberg told the TheDoctor.
When green tea is fermented to make black tea, the reaction causes the simple flavonoids found in green tea, called catechins, to form more complex flavonoids, called theaflavins and thearubigins.
Red wine and dark chocolate also contain flavonoids. But they pack a caloric punch. If you want a zero calorie source of a number of flavonoids, grab a cup of tea, advises Blumberg. “Whatever you drink per day, double it.” For iced tea, which is usually more diluted, make a full-strength cup and then add the ice to maximize the flavonoid concentration.
The longer tea is left to steep, the more flavonoids will be extracted from the leaf of the plant, until it reaches a saturation point, and flavonoids are no longer moving out of the leaves, Lambert says. Steeping temperature and the number of times lea leaves are used also have an effect on the concentration of flavonoids.
The flavonoids in tea exert antioxidant and anti-inflammatory direct or indirect effects against the inflammation that underlies the disease processes of conditions such as hypertension and cancer. Flavonoids either directly scavenge free radicals that can lead to inflammation or turn on enzymes that will do so. They can also turn off enzymes that form reactive oxygen species, molecules that cause inflammation.
Much of the evidence about tea and cancer comes from animal studies and long-term observational studies in humans, according to Lambert. Many animal studies look at how compounds other than flavonoids or pharmaceutical drugs potentiate, or affect, the anticancer effects of tea flavonoids. Further studies are needed to help scientists better understand the mechanisms by which flavonoids fight cancer.
Flavonoids also help prevent the blood clots that cause heart attacks and strokes. Investigators at Beth Israel Deaconess Medical Center and Harvard Medical School found that the flavonoid rutin inhibits an enzyme that contributes to blood clot formation, protein disulfide isomerase.
“Rutin is available in many foods, including tea,” says Robert Flaumenhaft, one of the researchers involved in the Beth Israel Deaconess Medical Center and Harvard Medical School study. The number of cups of tea necessary to see this vascular benefit remains to be determined. A bag of black tea contains about 175 mg of flavonoids.
Tea may help reduce the risk of diabetes by helping to regulate blood sugar. One recent study found diabetes was less common in countries with a rate of high black tea consumption. Another found that flavonoids in tea reduce the spike in blood sugar that follows the consumption of starchy foods.
Lambert's group gave mice corn starch and either green tea or not and found that a flavonoid in green tea called epigallocatechin-3-gallate (EGCG) significantly reduced the spike in blood sugar after the mice ate the corn starch. They also found that green tea did not have an effect on the digestion of simple sugars. This finding may have important implications for those with diabetes or high blood sugar who want to minimize the spike in their blood glucose after eating carbohydrates, Lambert says.
The antioxidant properties of tea also may reduce osteoporosis. People are living longer than ever before. As people age, they have a higher level of oxidative stress due to more reactive oxygen species, which can contribute to degenerative diseases such as osteoporosis, according to Leslie Shen, a professor of pathology at the Texas Tech University Health Sciences Center. Shen and her group studied 171 postmenopausal women with bone loss. Those who took a 500 mg capsule of green tea polyphenols (equivalent to about 4 to 6 cups of green tea) daily showed improved bone formation. Green tea polyphenols, both alone or combined with tai chi, also increased muscle strength.
Shen tells TheDoctor that her team recently received funding from the National Institutes of Health to continue their work, first with a dose optimization study in rats and then down the road in a larger group of postmenopausal women.
And what about herbal teas, also known as tisanes? They can be wonderful, but they are different than tea derived from C. sinensis, Blumberg says. Herbal teas contain lots of phytochemcials, but they are different phytochemcials, and they may have health benefits, but unfortunately, they are much less studied than tea.
Although the precise benefits of tea and the amounts needed for those benefits may not be clear, certainly no harm and definitely some antioxidant and anti-inflammatory benefits come with drinking tea. Watch the sweetener, though: tea's benefits in the metabolizing of sugar are just being discovered, but its health benefits should not be an excuse to consume more of the sweet stuff.