April 23, 2008
We're steeped in information about how green tea has cancer-preventing properties. But scientists are increasingly discovering the anti-cancer effects of other types of tea. Here's a roundup of research on how black, red and white tea can reduce the risk of a wide variety of cancers.
Black, green and white tea all come from the plant Camellia sinensis, which, according to legend, was discovered almost 5,000 years ago by the Chinese emperor Sheng Nung. The only difference between the types of tea is in which part of the plant is used and how those parts are processed. Green tea is made from withered leaves and buds that are fired or heated. Black tea is green tea that has been rolled and fermented. White tea, which is made only from the buds, is rapidly steamed and dried, making it the least processed of the lot.
Red tea comes from a South African flowering shrub known as rooibos (Aspalathus linearis). The needle-like leaves and stems are either bruised and fermented, or dried without fermentation. The fermented type is called red tea because of its distinctive color. The unfermented type is known as green rooibos, and according to a 2003 article in the American Botanical Council's Herbalgram, it has more antioxidants than the red version.
According to a 2001 research review published in Nutritional Biochemistry, tea—no matter what its color—is the best dietary source of a type of polyphenol known as catechin flavonoids. The authors of the study write: "It is evident that tea polyphenols exhibit many protective activities, and different metabolic pathways are involved. They act as antioxidants, they selectively inhibit specific enzyme activities, they target and repair DNA aberrations." They conclude that in vivo animal studies indicate that tea polyphenols can inhibit many types of cancer.
Next to green tea, black tea is the most researched variety of tea. Although green tea gets the headlines, according to a research review by scientists in the department of dermatology at the University of Wisconsin, Madison, 78 percent of the tea consumed worldwide is black.
"Research conducted in recent years reveals that both black and green tea have very similar beneficial attributes in lowering the risk of many human diseases, including several types of cancer and heart diseases," the authors write in the June 2004 issue of Antioxidants & Redox Signaling. "For cancer prevention, evidence is so overwhelming that the Chemoprevention Branch of the National Cancer Institute has initiated a plan for developing tea compounds as cancer-chemopreventive agents in human trials."
Black tea research includes:
In a study conducted by scientists at Rutgers University and reported in the January-February 2005 issue of Experimental Lung Research, caffeine and a type of polyphenol in black tea, known as theaflavin, were found to reduce lung tumor occurrence and size in mice.
A University of North Carolina study examined the effect of black tea intake on the risk of rectal cancer in 663 Moscow residents. The study, published in the July 2003 issue of the Annals of Epidemiology, found that the greater the intake of black tea, the lower the rectal cancer risk.
Writing in the December 2002 issue of the Journal of Experimental and Clinical Cancer Research, Indian researchers evaluated the effect of two black tea polyphenols—theaflavin and thearubigin—on leukemia cells. They concluded that the polyphenols inhibited cell growth.
Rooibos has been grown commercially in South Africa since World War II, but wasn't widely exported until the late 1990s. Consequently, fewer studies have been done on its link to disease reduction.
Although rooibos has both flavonoids and phenolic acids that act as antioxidants, according to a 2003 article in Herbalgram, one serving of rooibos tea has fewer polyphenols than the same size serving of green or black tea. However, the authors note, "The types of polyphenols in rooibos tea are different than those in green and black teas, so the potential health benefits of the teas cannot be compared solely on their total polyphenol content."
For instance, in a 1997 article in Food Chemistry, researchers analyzed the antioxidant capacity of various teas, and concluded that green tea had the strongest antioxidant activity (90.8 percent), followed by green rooibos (86.6 percent), red rooibos (83.4 percent) and black tea (81.7 percent).
Other research includes:
A study published in 1993 in Mutation Research found that rooibos was more effective than green tea at reducing cancer-associated changes in animal cells.
In a 2001 study in Mutation Research, scientists reported that orientin—a flavonoid found in rooibos—is a potent free-radical scavenger that reduced by half the number of cancer-associated changes in human blood cells exposed to radiation.
Two other rooibos flavonoids—quercetin and luteolin—have been shown in in vitro studies to cause pancreatic, thyroid and colon cancer cells to "commit suicide," according to four studies cited by Herbalgram.
In 2000, scientists at the Linus Pauling Institute at Oregon State University presented the first research on white tea, and concluded that this rare, delicate beverage may have the strongest cancer-fighting potential of all teas.
"Many of the more potent tea polyphenols become oxidized or destroyed as green tea is further processed into oolong and black teas," says Roderick Dashwood, Ph.D., principal investigator for the study. Chemical analyses done by his group found that white tea has more antioxidants than green tea. And a study also conducted by Dashwood's team and published in the March 2003 issue of Carcinogenesis found that the number of colon tumors in laboratory mice were reduced from an average of 30 to 17 after the mice were given green tea, and from 30 to 13 after consumption of white tea.
Anna Wassermann, spokeswoman for Oakland, Calif.-based Numi Tea, says the theory is that because white tea is made from the top bud of the tea plant, "there's a concentrated amount of nutrients, like with broccoli or cauliflower."
Best brewing method
Countless studies have shown that dosages determine how effective a tea is at fighting cancer. To get the best antioxidant levels, The American Botanical Council Clinical Guide to Herbs recommends steeping tea 15 to 20 minutes to maximize the yield of catechins, but admits this will make the tea bitter. Fortunately, diluting the caustic concoction with milk doesn't keep your body from absorbing the catechins.
Vicky Uhland is a freelance writer and editor in Lafayette, Colo.
Natural Foods Merchandiser volume XXVII/number 9/p. 28, 30
About the Author(s)
You May Also Like