Mouse
experiments suggest that folic acid deficiency could increase the
brain's susceptibility to Parkinson's disease, according to scientists
at the National Institute on Aging. In the finding, published in the
January 2002 issue of the Journal of Neurochemistry, the investigators
fed one group of mice a diet that included folate, while a second
group was fed a diet lacking this vitamin. They then gave the mice
moderate amounts of MPTP, a chemical that can cause Parkinson-like
symptoms. In the mice fed folate, MPTP caused only mild symptoms of
disease. But mice fed the folate-deficient diet developed severe Parkinson-like
symptoms.
The
scientists found that mice with low amounts of dietary folic acid
had elevated levels of homocysteine in the blood and brain. They suspect
that increased levels of homocysteine in the brain caused damage to
the DNA of nerve cells in the substantia nigra, an important brain
structure that produces dopamine. Loss of dopamine causes the nerve
cells to dysfunction, leaving patients unable to direct or control
their movement in a normal manner.
In mice fed adequate amounts of
folate, dopamine-producing nerve cells were able to repair damaged
DNA and counteract the adverse effects of homocysteine. However, similar
nerve cells in folate-deficient mice could not repair extensive DNA
damage. As a result, these cells died. "This is the first direct
evidence that folic acid may have a key role in protecting adult nerve
cells against age-related disease," said Mark Mattson, Ph.D.,
chief of the NIA's Laboratory of Neurosciences. "It is clear
from this study that a deficiency of this vitamin is associated with
increased toxin-induced damage to the dopamine-producing neurons in
the mouse brain."
People
who have Parkinson's disease often have low levels of folic acid in
their blood, but it is not clear whether this a result of the disease
process or if they are simply malnourished due to their illness. But
based on this study, Dr. Mattson speculates that consuming adequate
amounts of folic acid-either in the diet or by supplementation-could
help protect the aging brain against Parkinson's and other neurodegenerative
diseases. Green leafy vegetables, citrus fruits and juices, whole
wheat bread and dry beans are good sources of the vitamin. Food and
Drug Administration (FDA) regulations require the addition of folic
acid to enriched breads, cereals, flours, corn meals, pastas, rice,
and other grain products.
Parkinson's disease occurs when certain nerve cells die or become
impaired and can no longer produce dopamine. Without it, individuals
can develop tremor or trembling in hands, arms, legs, jaw, and face;
rigidity or stiffness of the limbs and trunk; bradykinesia, or slowness
of movement; and postural instability or impaired balance and coordination.
Patients may also have difficulty walking, talking, or completing
other simple tasks. The disease is both chronic and progressive. Parkinson's
is not usually inherited, but incidence of the disease increases with
age, with an average onset at about 60 years. It afflicts about 50,000
Americans annually.
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