Green tea is one of those magic brews praised as a cure for just about everything, so much so that it's become a symbol of health and serenity - peace in a cup.
From stress relief to weight control to lowering bad cholesterol, staving off dementia and preventing cancer, green tea is touted as nature's elixir.
Is it all it's cracked up to be?
All, or most, tea comes from the same plant, Camellia sinensis. Whether it's white, yellow, green, oolong or black depends on how its processed. Black tea leaves are oxidized completely, while green ones undergo minimal processing. So all teas derived from this plant have some of the purported benefits.
Will it save your life? Probably not. But it will likely do you some good.
What the experts say
"A cup of green tea has 50 to 100mg of EGCG [epigallocatechin gallate]. That's quite a lot. EGCG can cause cancer cells to die; that's well documented. The difficulty is that the concentration required also affects normal cells. Most of the studies of green tea done with cancer patients do not have positive results. For our research, we converted the natural EGCG into a prodrug to ensure it was better absorbed. At least three of our animal studies show that at the same dosage the prodrug is more effective than EGCG itself [in tea] in preventing the growth of breast, prostate and colon cancer. This is an animal model that has not been extended to humans."
TAK-HANG CHAN, professor emeritus of chemistry, McGill University, Montreal
"Green tea seems to act as a mild appetite suppressant. Black tea might have a similar effect, but green tea is lower in caffeine. And you get other benefits in terms of antioxidants. I use it for weight loss. Green and black teas both contain L-theanine, which helps somewhat to decrease cortisone, a stress hormone. That's where you get the anti-stress benefits. L-theanine balances the rise in cortisol that's caused by caffeine."
TARA ANDRESEN, naturopath, Toronto
"My lab works on attention, and we were interested in theanine. In studies looking at the impact of theanine on neural oscillations and their role in deploying attention, we consistently found effects of theanine, and a larger effect of caffeine, on these attention systems. Sometimes we've found a synergistic effect: when people consume these two, they are a little less inclined to make mistakes in vigilance tasks. Theanine and caffeine are in every kind of tea in much the same concentration. They are relatively small amounts, frankly. Many of our studies have been with larger doses - four to 10 cups of tea. It remains to be seen whether the concentrations in a single cup are meaningful. But if, over the course of a morning, someone has three to five cups, then likely the concentration levels are somewhat equivalent to those used in our study."
JOHN J. FOXE, researcher, Albert Einstein College of Medicine, Bronx, NY
"Our study used a specialized drink highly concentrated in green tea catechins. Subjects received either the tea or a control beverage, and they were on an exercise program for 12 weeks. We found that weight loss was not different between the subjects, but they had differences in body composition. People on the green tea beverage lost fat around their midsection. Our beverage's catechin content was equivalent to five to seven cups of brewed green tea. Our hypothesis is that there's a synergy between green tea and exercise. The catechins presumably affect enzymes that are part of the sympathetic nervous system and prolong the effects of epinephrine, a hormone that reduces body fat."
TIA RAINS, principal scientist, Biofortis Clinical Research, Addison, Illinois
"EGCG has been known to have preventive anti-cancer properties but fails to reach tumours when delivered by conventional intravenous administration. To overcome this problem, we encapsulated EGCG in a tumour-targeted delivery system. We demonstrated that this green tea extract formulation can have anti-cancer effects in laboratory settings: the intravenous administration led to tumour suppression of 40 per cent of the tested tumours. The studies didn't involve drinking tea, so I can't comment on that. The active compound EGCG would probably be too diluted to exert an effect."
CHRISTINE DUFES, senior lecturer, Strathclyde Institute of Pharmacy and Biomedical Sciences, Glasgow
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