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Tea's Many Health Benefits
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.
Drink Your Vegetables
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.
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.
Tea's Antioxidant and Anti-Inflammatory Benefits
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.
Fighting Cancer with TeaIn diseases characterized by rapidly dividing cells, such as cancer, flavonoids can turn off the machinery that causes the out of control growth of tumor cells. A lot of research has been done on green tea and cancer and black tea and cancer. Laboratory evidence definitely supports a preventative effect for flavonoids against several different types of cancer, including lung cancer, breast cancer, and skin cancer.
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.
The Heart of the MatterPreventing inflammation can improve vascular and function and blood flow. At a recent symposium on the health benefits of tea, Italian scientists presented research showing that giving black tea to study participants at the same time as a high-fat meal prevented the negative effects of such a meal on blood vessel function. Blood pressure usually increases and blood vessels are unable to dilate following a high-fat meal. However, when the researchers gave patients with mild high blood pressure a fatty meal and a cup of black tea at the same time, the patients’ blood vessels were able to function properly and their blood pressure was reduced.(1)
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.(2)
“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.