To Your Health

I sometimes feel calmer after drinking green tea despite its caffeine content. Could it be the theanine in the tea?

Q. I sometimes feel calmer after drinking green tea despite its caffeine content. Could it be the theanine in the tea? What exactly is theanine, and is green tea the only source? Is it missing in decaffeinated tea?

A. L-theanine is a chemical relative of L-glutamic acid, which is a powerful brain stimulant, but theanine has the opposite neurological effect. Most people report that theanine relaxes without causing drowsiness. In animal experiments it also protects brain cells from death by glutamic-acid poisoning. We often encounter glutamic acid as MSG, the flavor enhancer that is routinely used in Asian foods and blamed for a variety of bad reactions to these foods.

Theanine is the major amino acid in tea, comprising about half the total amino-acid content. It is a unique amino acid found only in tea and in a few mushrooms. Green tea contains a much higher concentration of theanine than other teas. A heavy green tea drinker (six to eight cups daily) will ingest between 200 to 400 milligrams of L-theanine daily.

All teas have some caffeine, even decaffeinated teas, but even regular green tea has only about one-third the caffeine of black tea. Because caffeine is chemically an "alkaloid" while theanine is an amino acid, the decaffeination process does not remove theanine. In addition, the ability of theanine to block caffeine's stimulation is much greater than caffeine's ability to stimulate, so 80 milligrams of theanine in a cup of green tea more than offsets the 10 milligrams of caffeine.

Theanine increases brain levels of gamma amino butyric acid, a calming neurotransmitter, while caffeine decreases it. Theanine also affects levels of both serotonin and L-dopamine neurotransmitters in the brain. Serotonin is one of the major mood-enhancing neurotransmitters, and dopamine is our "reward" neurotransmitter.

By shutting down the "worry" mode and increasing the ability to concentrate and focus one's thoughts, as measured by increased generation of brain alpha waves, some believe that theanine even makes learning easier.

Studies in Japan have shown that women taking 200 milligrams of L-theanine daily have a lower incidence of PMS symptoms. Overall, the women reported a 60% reduction of symptoms.

The benefits of theanine do not end with its recognized calming effect. Coffee consumption has long been suspected to increase the risk of heart disease. Green tea consumption, on the other hand, reduces this risk by about half.

In other research, theanine enhanced the anti-tumor activity of the cancer drug doxorubicin by inhibiting its loss from tumor cells. A dose of doxorubicin that was ineffective when used alone was successful at inhibiting tumor growth when theanine was added. Simultaneously, doxorubicin concentrations decreased in normal tissues and increased inside the tumor, which means less of the drug could be used and side effects minimized.

Studies show that theanine is virtually nontoxic and can probably be used by everyone. In our stressful world, it is difficult to overestimate the benefits of a simple substance that appears to relieve much of the "stress of life."

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