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Green tea
catechins, until recently thought to work simply as antioxidants, are
now known to invoke a wide spectrum of neuroprotective cellular mechanisms.
These include iron chelation, scavenging of free radicals, activation
of survival genes and cell signaling pathways, and regulation of mitochondrial
function. (The mitochondria are the energy production factories inside
our cells. When they are not working properly, they generate many free
radicals and little energy.) The end result is a significant lessening
of damage to brain cells.
Iron accumulation
in specific brain areas and free radical damage to brain cells are considered
the major damaging factors responsible for a wide range of neurodegenerative
disorders including both Parkinson's and Alzheimer's disease.
In the
brain, epigallocatechin-3-gallate (EGCG) has been shown to act as an
iron chelator, binding to and removing iron, thus preventing it from
contributing to the production of free radicals. In addition to removing
iron, EGCG also increases the activity of two major antioxidant enzymes,
superoxide dismutase (SOD) and catalase, further helping to decrease
free radical damage.
Another
active compound in green tea, epicatechin (EC), reduces the formation
of a protein called amyloid-beta. Plaque-like deposits of amyloid-beta
in the brain are a defining characteristic of Alzheimer's disease.
Animal
studies conducted at the Douglas Hospital Research Centre, McGill University,
Quebec, Canada, suggest that a daily cup or two of either black or green
tea may reduce the risk of age-related degenerative brain disorders
such as Alzheimer disease.
The researchers
looked at the protective effects of two tea extracts and their main
constituents, epigallocatechin gallate and epicatechin gallate, which
are highly concentrated in green tea, on dying nerve cells. Both black
and green tea extracts and catechins strongly blocked death of neurons
(brain nerve cells) When researchers exposed cultured neurons to amyloid
alone, its effects were so toxic that the brain cells died, but when
the cell cultures received amyloid immediately followed by tea extracts
and catechins, the neurons were rescued and survived.
Green tea
polyphenols have also demonstrated the ability to affect cell signaling
pathways, in particular the MAPK pathways, which are triggered by oxidative
stress (free radicals), and themselves set in motion a series of chemical
reactions so damaging that they can result in brain cell death. MAPK
signaling pathways inside brain cells are thought to play a critical
role in neurodegenerative diseases.
Another
important cell signaling pathway beneficially affected by EGCG, the
PKC pathway, is also thought to play an essential role in the regulation
of cell survival and programmed cell death.
Although
no human studies on Alzheimer's disease have yet reported benefit from
tea consumption, recent population studies have shown that simply consuming
2 or more cups of green tea daily reduces risk of cognitive decline
and Parkinson's disease.
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