The health benefits of green tea

Tea Off

I recently received an e-mail from an HSI member who asked why I don’t give more attention to the health benefits of green tea.

Good question, because many studies have shown that green tea boosts antioxidant activity and may offer protection against certain cancers. But if I wrote about every green tea study or commentary that I came across, the e-Alert could easily turn into the Green Tea-Alert.

That said, today I’ll give some well-deserved attention to a recent study that provides promising conclusions about the way green tea helps prevent cancer, as well as a surprising warning for many women who drink green tea daily.

Block that enzyme

About one third of the dry weight of green tea leaves is made up of a flavonoid called catechin. The most abundant of the four types of green tea catechins is epigallocatechin gallate (EGCG), which also happens to be the component of green tea that has been shown to inhibit tumor cell growth.

Researchers with the John Innes Centre in Norwich, UK, and the University of Murcia in Spain, launched a laboratory study of EGCG after their research showed that the chemical structure of a cancer drug called methotrexate was remarkably similar to ECGC.

As reported in the journal Cancer Research, the researchers isolated EGCG from green tea leaves and tested its effect on an enzyme called dihydrofolate reductase (DHFR), which promotes cancer cell growth by producing new DNA in cancer cells. The test revealed that EGCG levels found in tissue and blood samples of green tea drinkers was sufficient to effectively bind DHFR, inhibit cell growth and induce apoptosis, a series of reactions that cause cancer cells to self destruct.

That’s the good news. Now for the warning

The researchers found that high levels of EGCG may reduce folate levels. The average green tea drinker can address this by increasing dietary sources of folate (chicken liver, lentils, asparagus and spinach) and by taking a folic acid supplement. Pregnant women, however, should be especially cautious because low folate levels increase the risk of causing neural tube disorders to unborn children. People with cardiovascular problems also need to keep folate levels high.

For specific advice from HSI Panelist Allan Spreen, M.D., about folic acid supplementation see the e-Alert “The B List” (2/2/04).

A couple of cups

The UK/Spanish researchers noted that the EGCG levels that inhibited cancer could be reached with about two or three cups of green tea per day. This finding is remarkably similar to another green tea study I told you about last year in the e-Alert “Envy With Green” (4/21/04).

In trying to understand the mechanism that makes EGCG effective against cancer, researchers at Kyushu University in Japan focused their attention on a type of cancer receptor cell known as 67 LR. Many cancer tumors produce large amounts of this cell, which senses chemicals and responds with electrical signals. Scientists believe that 67 LR is one of the key agents that helps cancer spread throughout the body. Using lung cancer cells, the researchers observed that cell growth was inhibited by exposure to EGCG at concentrations that would equal just three cups of green tea.

Shortly after the Kyushu study was released, another study of EGCG was reported in the journal Blood. Researchers from the Mayo Clinic in Rochester, Minnesota, examined the interaction between EGCG from green tea and cancer cells taken from 10 patients diagnosed with the most common type of leukemia: B-cell chronic lymphocytic leukemia (CLL).

This research also involved a receptor cell, called VEGF, which nurtures growth in leukemia. Researchers found that EGCG suppressed the VEGF mechanism, inhibiting the growth of new blood vessels necessary for cancer proliferation. In 8 of the 10 samples, EGCG prompted the death of cancer cells.

The Mayo Clinic researchers hope their study will eventually lead to a non-toxic way to treat CLL. This type of leukemia can only be treated with chemotherapy, but when older patients are diagnosed with early stages of CLL (a cancer that mostly affects people over the age of 60), some doctors choose to monitor the slow-growing disease before subjecting a patient to unnecessary (and harsh) treatments. The Mayo team believes that EGCG could be an effective, low-impact treatment for early stage CLL.

To Your Good Health,

Jenny Thompson
Health Sciences Institute


Sources:

“The Antifolate Activity of Tea Catechins” Cancer Research, Vol. 65, No. 6, 3/15/05, cancerres.aacrjournals.org

“Scientists Find How Green Tea Fights Cancer” Reuters, 3/15/05, reuters.com