"The problem with stroke is so much damage can happen so quickly," she says. "It's possible that something in tea is protecting the brain from the damage of stroke."
That's not to say L-theanine is the protective factor, but it has a chemical structure similar to that of glutamate, a cell-damaging substance released during a stroke. Thus, one hypothesis is that L-theanine's presence may block glutamate receptors during a stroke, limiting brain damage.
* Researchers are also exploring whether the substance could benefit people with mood and neurocognitive disorders.
A study of 60 people with schizophrenia found those taking L-theanine along with antipsychotic medications had fewer emotional and cognitive symptoms compared with patients taking a placebo and antipsychotic medications. The study, by Dr. Michael S. Ritsner of Technion-Israel Institute of Technology, is undergoing review for publication.
Sorting it out
Of course, it's possible that L-theanine may not have the same positive health effects if separated from the other chemicals found in tea, which is also rich in antioxidants.
"Based on what we know now, I'd stick with drinking tea," Arab says when asked about the possible benefits of the L-theanine supplements or drinks with L-theanine.
There is some evidence that L-theanine works better in conjunction with caffeine.
The dose also matters. The L-theanine contained in a cup of tea ranges from 2 milligrams to 100 milligrams, Bukowski says. In L-theanine studies, the dosages range from 50 milligrams to 400 milligrams. There is no known toxic dose of L-theanine or any reports of harm from the substance.
The dose found in energy drinks ranges from 50 milligrams to 200 milligrams, says Taiyo's Smith. Studies show that the effects increase with the dosage. L-theanine tends to stay in the brain for about six hours, Foxe says.
But, he cautions: "These are laboratory tests of attention. What this means for people driving a car, we don't know. It's not going to turn you into Tiger Woods. I don't know that it will take even two strokes off your game. My personal opinion is there is a lot of science to be done. The science is good, but very little has been done."
The effects are clearly subtle, adds Bukowski, who has performed consulting work for Taiyo.
"For someone who has to really concentrate, for example, in golf where you have to really concentrate while putting the ball and striking the ball, it could help keep your game plan in check without being jittery and emotional," he says.
