Steeped in science
When it comes to a societal tonic, Americans have long preferred coffee over tea. But although coffee may be good, it’s increasingly hard to ignore the evidence that tea is good for you.
Long viewed simply as a reason to relax in the middle of a stressful day or as a folk remedy for colds and digestive problems, mounting research suggests that drinking tea could lower the risk of developing several serious illnesses, including heart disease, cancer and osteoporosis. Almost 300 tea studies were completed last year alone.
Tea is as hot among consumers as it is among researchers. In the United States, sales rose from $1.84 billion in 1990 to an estimated $5.03 billion in 2002, according to the Tea Council of the USA, a trade organization. Though consumption per person still lags far behind that of many countries, the numbers reflect a soaring interest in this ancient brewed drink.
The recent findings have made a believer out of Andrea Emmerich, 38, who was shopping recently at Elixir Tonics & Teas, a store and tea garden on Melrose Avenue. Emmerich was choosing from bowls of high-quality, loose tea leaves selling at $2.75 to $9 an ounce. A few years ago, Emmerich said, she decided to change her lifestyle to become healthier. “And I got into this whole tea world.
“I pay attention to the health benefits from tea. It’s medicinal,†said Emmerich, who lives in Los Angeles and is a student of Ayurvedic medicine. “I quit drinking caffeinated coffee three years ago. Then I went to decaf coffee. Then I went to tea.†No one is saying that tea is a cure-all or that you should drink it daily for good health, said Jeffrey Blumberg, a tea researcher at Tufts Nutrition Center in Boston. “The evidence is compelling that something is going on,†he said. “But I wouldn’t call it definitive.â€
Many researchers expect that to soon change. They’re pushing ahead with studies that should answer whether tea can help prevent certain diseases.
The belief that tea improves health began with epidemiology, observations that certain tea-drinking cultures have a lower incidence of disease. For example, the Japanese, who drink tea with most meals, have much lower rates of heart disease than Americans, who are not big tea drinkers.
Such observations are obviously not proof -- the English, who practically bathe in tea, show no special protection against heart disease -- hence, the need for better research.
“There has been a lot of epidemiology looking at tea, and it’s, at best, sort of mixed,†says Dr. Ken Mukamal, an internist at Beth Israel Deaconess Medical Center in Boston. “Some studies have found striking beneficial effects, and others really haven’t shown that; so there is this area of controversy.â€
Recent research has focused on biomarkers, measurements of specific substances or chemicals in the body, that can reveal what is happening -- such as whether tea consumption lowers cholesterol or kills harmful bacteria in the stomach. (Studies show tea does both.)
Still to come are large clinical trials in which people are assigned to drink a certain amount, and quality, of tea in a controlled setting over long periods of time. The tea drinkers’ rates of disease will then be compared with the rates of those who don’t drink tea.
But even without the research, scientists have a good idea of why tea appears to confer a broad range of health benefits. Tea -- whether it’s black or green or oolong -- contains compounds called polyphenols, or flavonoids, powerful antioxidants that can eliminate free radicals that damage cells. Free radicals are produced naturally in the body as byproducts of chemical processes.
Because the antioxidants in tea are so powerful -- one study estimated that tea antioxidants are 30 times more potent than the antioxidant vitamins C and E -- they are believed to have an impact on many different areas of the body and on various disease processes.
Tea polyphenols are similar to the substances that make certain fruits and vegetables so healthful. Some researchers suggest that tea polyphenols confer a wide range of benefits because they are absorbed at different points throughout the digestive tract.
The amount of time tea is fermented during processing -- which determines whether it becomes black, green or oolong -- can alter the types of polyphenols found in tea, and some scientists are trying to identify which particular polyphenols may be the most powerful. Identification of specific polyphenols might even lead to drugs based on that substance. But other researchers believe that the entire range of polyphenols found in tea is what provides its preventive punch, Blumberg said.
“Tea is not all that complicated,†he added. “It’s not like it has 10,000 different compounds. In terms of trying to attribute what these health benefits are due to, well, there is not that much in tea, other than flavonoids.â€
Here’s a look at some of the strongest recent evidence about tea and specific ailments.
Heart disease
Polyphenols interfere with the free-radical molecules that cause low-density lipoprotein (or “badâ€) cholesterol to form plaque inside the heart’s arteries. Some studies have shown that polyphenols have anti-clotting effects and can relax blood vessels, which makes them function better.
Such findings imply that tea could reduce the risk of heart disease or help tea drinkers fare better after a heart attack. In a study published last year in the journal Circulation, Mukamal followed more than 1,900 people who had suffered a heart attack. Almost four years later, heavy tea drinkers (14 or more cups a week) had a 44% reduced risk of dying compared with nondrinkers. Even patients who were moderate tea drinkers (less than 14 cups a week) showed some added protection compared with nondrinkers.
If the study findings can be duplicated and tea does indeed reduce heart attack deaths, “that is a major public health benefit,†he said.
A Dutch study published last year also found that tea drinkers had half the risk of having a heart attack, and one-third the risk of a fatal heart attack, compared with nondrinkers.
An important component of both the Mukamal and Dutch studies was that the participants, men and women mostly in their 60s, were similar in other ways, such as education, income, exercise habits, smoking and drinking habits. That’s important because some researchers suggest that it may not be the tea that keeps tea drinkers healthier but other aspects of their lifestyle, such as dietary habits and exercise. “Maybe it isn’t just an artifact of healthier people drinking tea,†Mukamal said.
Cancer
Various studies have suggested tea may reduce the risk of bladder, stomach, colorectal, esophageal and oral cancers.
Dr. Zuo Feng Zhang, a researcher at UCLA’s Jonsson Cancer Center, published a study in 2001 showing that drinking green tea can reduce the risk of chronic gastritis by half. Chronic gastritis is an inflammatory disease that causes precancerous lesions, which can progress to stomach cancer.
“This is a very promising area,†says Zhang. “The polyphenols can prevent cancer and also have vitamins C and E, which are very good for people’s health. We have very strong confidence that the effect we found with chronic gastritis is real.â€
Zhang plans on conducting a randomized trial to see if drinking tea can prevent precancerous lesions in the stomach. In the meantime, he and his colleagues at UCLA have launched the largest clinical trial ever focusing on bladder cancer in smokers and former smokers. (Tobacco use is a major risk factor for bladder cancer.) Investigators will give the study participants a green tea extract or an experimental drug called Iressa to gauge their effects at preventing cancer. Previous laboratory research at UCLA showed that green tea can reduce the growth of bladder cancer tumors in both animal and human models.
Zhang’s work on stomach cancer is among several studies suggesting that tea has preventive properties. A 1994 study in the Journal of the National Cancer Institute found that drinking green tea reduced the risk of esophageal cancer by 60%, while a study presented at the Third International Symposium on Tea and Human Health last fall in Washington found that women who consumed high amounts of tea had a 60% reduced risk of rectal cancer. Researchers at Rutgers University have even identified a compound in black tea, called TF-2, that caused colorectal cancer cells to die in laboratory experiments while normal cells were unaffected.
Osteoporosis
Taiwanese researchers last year announced that longtime tea use appears to strengthen bones. The study, published in the Archives of Internal Medicine, found that hip bone density was 6.2% higher in people who drank tea habitually for 10 years or more, compared with nondrinkers. People who drank tea regularly for six to 10 years had a 2.3% higher bone density.
A British study, published in 2000 in the American Journal of Clinical Nutrition, also found higher bone density in women who drank at least one cup of tea a day.
Tea may confer a protective effect on bones because it contains both fluoride and phytoestrogens, substances that act like estrogen, which is known to strengthen bone.
Other benefits
Early research suggests that tea can inhibit the growth of bacteria on teeth and that a white tea extract cream can protect against cellular changes in the skin caused by sun damage. But these studies have been small and preliminary, and much further work is needed.
The most common therapeutic use for tea in the United States -- to ease cold symptoms -- is also getting a closer look by scientists. A particular compound found in green tea, methylated epigallocatechin gallate, can block the production of two substances in the body that cause sneezing, watery eyes and coughing.
And there may be yet another reason to drink tea, adds Blumberg. He calls it the “substitution effect.â€
“How do you go about making healthy food choices? Many Americans choose soda. But if you drink tea, you may not be having some of this stuff that’s not good for you.â€
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Tea consumption
Number of pounds of tea each person consumes on average each year, by country. Each pound equals about 200 servings.
United States ...0.72
Japan ...2.5
England... 5.0
Kuwait ...5.0
Ireland... 5.9
Source: International Tea Committee (figures from 1999-2001)
