The new finding, reported today at the annual meeting of theAmerican Academy of Neurology in Denver, explains how ingredients plentiful in green tea can help the flow of a brain chemical that's at the heart of this devastating disease.
"In our study, we demonstrate the inhibitory effects of green teapolyphenols," on mechanisms directly involved in Parkinson's disease,says study author Dr. Tianhong Pan, a researcher from China who wasworking at Baylor College of Medicine in Houston during the study.Pan says she and her colleagues in China began the animal study -- a joint effort between the National Cancer Institute and the Chinese government -- because of the lower rates of Parkinson's disease among populations where green tea is heavily consumed.
"The prevalence of Parkinson's disease was lowest in Asia and Africa, where green tea is commonly consumed, so it seems that there is some relationship between green tea consumption and the occurrence of [this disease]," Pan says.
For neurologist Dr. Souhel Najjar, this is the first research to document the mechanism by which green tea can protect the brain.
"That mechanism involves the transport of the brain chemicaldopamine, which plays a key role in Parkinson's disease," says Najjar,a Parkinson's disease specialist.
Proving green tea can work on that transport system could bekey to learning how to prevent the disease, Najjar says,who adds it could also open the door to new treatment strategies.
Pan agrees: "The results suggest that green tea may have potential both in the treatment and protective effects in Parkinson's disease."
The mechanism explored in this study involved the transport ofdopamine from the area of the brain where it is made to a secondarea where it is utilized, movement that is critical in Parkinson's disease.
"Normally, dopamine is made an area of the brain called thesubstantia nigra, and it travels a pathway to a second area of thebrain known as the striatum," Najjar says. Sometimes, however, too much of the dopamine flows back into the substantia nigra. That leaves the striatum with less dopamine than it needs to function properly.
Because dopamine helps muscles move smoothly andefficiently, when a deficiency occurs, symptoms ofParkinson's develop -- including muscle rigidity and tremors.
In the new study, however, researchers demonstrated thatcompounds known as polyphenols can block the back flow of dopamine, so the transport continues, unhampered, from one area of the brain to the other.
"By keeping the transport of dopamine from being disrupted,polyphenols might be able to reduce the risk of Parkinson's disease,as well as reduce the progression of the disease in those alreadyaffected, " Najjar says.
Although both doctors are optimistic, no one is certain the results willapply to humans. Pan's group tested levels of dopamine in mice, and then treated some with polyphenols while leaving others untreated.
They then injured the specific neurons or brain cells linked to Parkinson's disease in all of the mice, and measured dopamine levels again.
The result: Those mice treated with polyphenols appeared to beprotected from the assault on brain cells. Pan reportspolyphenols were able to "inhibit the uptake of dopamine byblocking the dopamine transporter."
"In this way, green tea may serve to protect against Parkinson's,particularly in the face of toxic elements that may be linked to thisdisease," Najjar says.
However, can drinking green tea help people as much as it helps mice?
"Although green tea polyphenols have numerous biological effectsin vitro, and epidemiological studies have shown some health benefits intea consumption, what is not clear at this time is whetherpharmacologically effective doses of green tea polyphenols can beattained in blood or tissues simply by consuming tea infusions," Pan says.
Najjar says it's possible, but based on this study "there is notenough evidence to make any kind of recommendation."
In addition to green tea, polyphenols are found in black tea,grapes, red wine, chocolate and other plant sources.
What To Do
To learn more about Parkinson's disease, you can visit the Parkinson's Disease Foundation.
For more information on the health benefits of green tea and othersources of polyphenols, check out University of Shizuoka, Hamamatsu College.