By Jill Max, HealthAtoZ contributing writer
After water, tea is the most commonly consumed beverage in the world, and drinking it has been linked to a slew of health benefits. Now recent research shows the billions of people who drink it may be on to something.
The heart of the matter
Tea may give you a stronger heart. A study in the journal Circulation: The Journal of the American Heart Association found that heart patients who drank a lot of tea were less likely to die three or four years after a heart attack.
Researchers at Beth Israel Deaconess Medical Center and the Harvard Medical School interviewed 1,900 patients who had been hospitalized after a heart attack. The people in the study were asked about how much tea they drank in the past year. They were divided into three groups: non-drinkers, moderate drinkers (less than 14 cups per week) and heavy drinkers (14 or more cups per week). After a follow-up period of almost four years, the moderate group was 28 percent less likely to die while the heavy use group had a 44 percent lower death rate, after taking into account differences in lifestyle (such as smoking and exercise) and medical conditions.
"If the true effect of tea in clinical trials is anywhere near what we saw, this will be of great public health importance," says Kenneth Mukamal, M.D., assistant professor of medicine at Harvard Medical School and an associate in medicine at Beth Israel Deaconess Medical Center.
What's in those tea leaves?
The power of tea may be from the antioxidants it contains known as flavonoids, which are thought to help prevent heart disease. Flavonoids may have an anti-clotting effect meaning blood is less likely to clot. Blood clots lead to heart attacks and strokes. Flavonoids are naturally in green and black tea, as well as in other foods such as apples, onions and broccoli.
A study in the journal Current Opinion in Lipidology looked at previously published research on the health benefits of tea and found that 150 milligrams of flavonoids - the amount found in a cup of brewed tea - was enough to have an immediate antioxidant effect. Consuming higher doses of flavonoids, or additional cups of tea, increased the effect.
Drinking tea may fight cancer
It's not just flavonoids. Tea also has catechins, another powerful antioxidant belonging to a group of chemicals known as polyphenols. Green tea, which is the least fermented type of tea, contains the most catechins, followed by oolong and black teas. Research has shown that catechins may stop cancer growth and protect healthy cells.
At a meeting of the American Association for Cancer Research, researchers at the University of Southern California presented a study that showed tea drinkers were about half as likely to develop stomach or esophageal cancer as people who didn't drink tea.
More than 18,000 men were followed, and the 232 subjects who developed one of these types of cancers were compared with 772 similar men without cancer. Researchers measured epigallocatechin (EGC), a substance that's produced when catechins break down, and found that the men who had more EGC in their urine had a lower cancer risk.
Research has shown that tea can help fight other types of cancer as well. A study in the journal General Dentistry found polyphenols in green tea killed mouth cancer cells in the lab while leaving normal cells unharmed. Another study presented at the Annual Meeting of the American Academy of Neurology found that green tea may have a protective effect on Parkinson's disease. Polyphenols were shown to protect neurons in the brains of mice by blocking a toxin that plays a role in the disease.
Tea and weight loss
The claim that drinking tea leads to weight loss has been widely touted, although little research has been done to back it up. One study from the University of Chicago's Tang Center for Herbal Medicine Research found rats injected with epigallocatechin gallate (EGCG), a substance in green tea, weren't as hungry and consumed up to 60 percent less food after a week of daily injections.
Researchers at the Beltsville Human Nutrition Research Center in Beltsville, Md. did a different type of study in humans. They compared the energy expenditure of 12 men who consumed each of four treatments: Water, full-strength oolong tea, half-strength oolong tea and water containing caffeine. To do this, the men had to spend 24 hours in a room calorimeter, a small room where, by measuring how much oxygen they consumed and how much carbon dioxide they produced, researchers were able to calculate how many calories they burned. Although the increase in energy expenditure - about 3 percent - was similar for the full-strength tea and caffeinated water, fat-burning increased by 12 percent when the men drank full-strength tea.
"Tea tended to raise metabolic rates, but to meet that demand, the body burned more fat," says William Rumpler, Ph.D., a research physiologist at Beltsville, Md. As to whether tea has a place in a weight loss program, he says it's an open question.
The jury is still out
Many of these studies are promising but are far from ironclad proof.
"I'm not sure our study means people should fill up their cupboards with tea," Mukamal of Harvard Medical School says. "But it points to the possible health benefits." Considering there are no risks to drinking tea - if you don't load it up with sugar and whole milk - he says it may make sense to discuss it with your doctor about adding it to your diet.
This article was reviewed and updated June 2007.
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