In studies, tea drinking has been shown effective in lowering high cholesterol and in cancer prevention. But researchers are still trying to figure out how. Likely, it is because the polyphenols in tea are strong antioxidants capable of "mopping up" DNA-damaging free radicals in the bloodstream.
Two studies in this month's Journal of Nutrition look at tea's health effects -- finding evidence that tea works, although exactly how is still a mystery.
The studies were presented at the Third International Scientific Symposium on Tea and Human Health, held today in New York City.
Black Tea and High Cholesterol
One study looks at the effects of black tea on total and LDL "bad" cholesterol in adults who had mildly high cholesterol levels. Each was on a carefully controlled diet; each was asked to drink five servings of black tea daily for three weeks. In the study's second phase, they switched to a placebo non-caffeinated beverage prepared to match the tea in color and taste. In the third phase, caffeine was added to the placebo, enough to equal that in tea.
Black tea reduced total cholesterol by 4% and LDL cholesterol by 8% compared with the effects of a placebo drink with no caffeine. When compared with a placebo with caffeine, total cholesterol was reduced by 7% and LDL cholesterol by 11% in participants consuming black tea.
The drop in cholesterol from 4% and 7% in those who consumed black tea means a decreased risk from heart disease, since a 1% decrease in cholesterol translates into about a 2% decrease in heart disease.
This could translate into an 8% to 13% decreased risk of heart disease, writes lead researcher Michael J. Davies, PhD, with the Beltsville Human Nutrition Research Center, a division of the U.S. Department of Agriculture.
However, tea did not affect the patients' antioxidant levels, Davies writes. It's possible that tea limits cholesterol absorption in the intestine.
Tea and Cancer
Researchers in this study monitored urine levels of 8-OhdG, a measure of overall damage to DNA. Smoking is associated with high levels of this by-product .
DNA damage, If not repaired, can result in genetic mutations that -- over a lifetime -- are expected to affect a person's risk of cancer, writes lead researcher Iman A. Hakim, PhD, director of Health Promotion Sciences at the Arizona Cancer Center at the University of Arizona.
Because 8-OhdG is easy to identify in the urine, it provides a way for researchers to monitor whether cells have been damaged, he explains.
His study involved 143 men and women -- all heavy smokers -- divided into three groups. For four months, each group drank four cups a day -- one group drank decaffeinated green tea, the second group drank decaffeinated black tea, and the third drank water.
In the end: The green tea group had the lowest 8-OhdG levels; the black tea and water drinkers had no change in 8-OhdG levels. Black tea and water, therefore, seemed to have no effect in protecting smokers from DNA damage.
Green tea, however, significantly cut the cell damage in these heavy smokers, a sign that drinking tea daily could be effective in cancer prevention, writes Hakim.
Coffee drinkers, it's a message: Switching to tea can lower high cholesterol and help with cancer prevention.