Antioxidants called polyphenols are thought to be responsible for tea's health benefits.
In a new study, antioxidant activity over eight hours was small but significantly greater after taking green tea extract supplements compared with drinking green or black tea, writes researcher Susanne M. Henning, with the Center for Human Nutrition at the David Geffen School of Medicine at University of California, Los Angeles.
Her study appears in the December issue of The American Journal of Clinical Nutrition.
"Green and black tea polyphenols have been extensively studied as cancer chemopreventive agents," she writes. Many laboratory studies have shown green and black tea to have antioxidant activity, but it's unclear how much of an effect this has in humans.
Some studies have pointed to the effectiveness of green and white tea in the prevention of colon cancer. Other studies have shown the effectiveness of black tea in preventing heart disease by lowering "bad" LDL cholesterol.
While both black and green tea comes from the Camellia sinensis plant, the processing they undergo determines the amount of polyphenols.
Green tea and green tea supplements generally contain higher amounts of polyphenols than black tea. "However, Darjeeling and Ceylon black teas contain unusually high amounts of [polyphenols]," she writes. Those were the black teas used in this study.
Few studies have looked at whether or not the body's absorption of these polyphenols is affected by drinking tea or taking tea extract supplements.
Green Tea vs. Black Tea
Her study examined absorption of liquid green or black tea, and green tea extract supplements in a group of 30 healthy men and women under the age of 40. Each was assigned to either green tea, black tea, or green tea extracts -- one week for each drink type or supplement.
Volunteers came to the UCLA lab for their daily tea. UCLA staff carefully prepared the hot black and green tea, using four black tea bags or three green tea bags added to 15 ounces of water and steeped for five minutes. The number of tea bags was chosen to provide the same amount of polyphenols contained in the green tea extract supplements, she explains.
Cups of tea were served immediately with or without sugar or milk. After each week of daily tea, volunteers had a "no-tea week." Blood levels were collected before and hours after drinking the teas or the extract.
Even though liquid black and green teas had more polyphenols than the supplements, more polyphenols were absorbed into the body with the supplements.
Green tea supplements produced the highest levels of antioxidants in the blood compared with liquid black or green tea.
The researchers say that the study shows the potential of future therapies in chemoprevention with supplements of tea polyphenols.