In December 2005, the Mayo Clinic in Rochester, Minn., released a case study suggesting green tea improved the conditions of four people with chronic lymphocytic leukemia.
The four patients consumed over-the-counter products containing epigallocatechin-3-gallate (EGCG), the active ingredient in green tea. Hematologist Tait Shanafelt, M.D., and colleagues tracked the patients' conditions, and preliminary evidence suggested positive clinical effects. The findings appeared in the journal Leukemia Research.
Green Tea: Miracle Cure?
The Chinese have consumed green tea for some 5,000 years. It contains antioxidants called flavonoids - also found in leafy vegetables - which are thought to prevent cancer.
Green tea has been used to treat hypertension and atherosclerosis. Studies have shown EGCG to modulate the growth factor leading to leukemic cells, while theaflavin-enriched green tea extract has been shown to lower cholesterol and may reduce the risk of hypertension.
Researchers such as Thomas Gasiewicz, Ph.D., chair of the Department of Environmental Medicine at the University of Rochester (UR) in New York, have studied green tea's chemopreventive abilities.
In 2003, Gasiewicz and his colleagues at UR 's Environmental Health Sciences Center determined that chemicals in green tea shut down the aryl hydrocarbon (AH) receptor, one of the key molecules in tobacco that may spur cancer.
Chemicals in green tea successfully shut down the AH receptor in cancerous cells in mice. The manner in which green tea is metabolized in the human body is still not fully understood, so more research is needed, according to Gasiewicz.
"The data from studies on human populations are not convincing as to a health benefit of green tea consumption," Gasiewicz said. "Some studies show some benefit; some studies do not. However, the evidence from animal investigations is more convincing for an anti-cancer activity of green tea and its components."
"Determining how these chemicals work in animals may help us to understand how they might - or might not - act in humans and the concentrations that may be effective. This information may also assist in the design of agents that may be more effective in humans for anti-cancer therapy," he said.
The Mayo Clinic research team also stated that more studies are needed to determine optimal doses, side effects and the frequency of medication before green tea can be recommended for widespread use among cancer patients.
FDA Weighs In
The U.S. Food and Drug Administration (FDA) says there's no concrete scientific evidence to support claims that green tea prevents cancer.
In a June 2005 statement, the FDA cited studies with conflicting information about the effectiveness of green tea in preventing certain types of cancer. While two studies revealed that green tea didn't demonstrably reduce the risk of breast cancer, one "limited" study suggested that it might. Similarly, while one study found that green tea didn't reduce the risk of prostate cancer, a smaller study found that it did.
As part of the FDA's Consumer Health for Better Nutrition Initiative, experts concluded that it is highly unlikely that green tea reduces the risk of breast cancer and prostate cancer. The FDA also concluded that qualified health claims for green tea consumption as a preventive measure for reducing the risk of other types of cancers must be investigated further, as no substantial scientific evidence exists for such claims.
Should You Go Green?
Bradly P. Jacobs, M.D., M.P.H., chair of the Complementary and Alternative Medicine Channel for myDNA.com's Medical Advisory Board (MAB) said people who drink green tea tend to be more health-conscious, which could account for their lower cancer risk.
"Studies in Asia show that cancer is lower among those drinking green tea," he said. But "this could be a lifestyle issue."
Green tea may not prevent cancer, but it does have plenty of proven health benefits.
"Studies have shown that green tea - either oral or topical - has significant antioxidant, anti-inflammatory and anti-aging benefits," said Lisa Zanetti Rhodes, M.D., co-chair of the Skin Disorders Channel for myDNA.com's MAB.
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