Environmental Link to Parkinson's Risk
Friday March 30 1:29 PM ET
By Melissa Schorr
SAN FRANCISCO (Reuters Health)
- Environmental factors
including pesticides, herbicides and fungicides may play a key role
in the development of Parkinson's disease, researchers suggested
Thursday at the annual meeting of the Society of Toxicology.
Scientists have debated for decades whether Parkinson's, a neuro-
degenerative disease affecting 1 million Americans, is caused mainly
by genetic or by environmental factors, said Dr. Bill Langston, president
of the Parkinson's Institute in Sunnyvale, California. Parkinson's occurs
when nerve cells in the part of the brain that controls movement are
damaged, leading to symptoms such as tremors, rigidity and loss of
But researchers have recently come to believe that while genetics
may play a strong role for those who develop the disease early in life, environmental factors probably trigger the vast majority of cases in
people who develop the disease later. Researchers also believe that
those who do develop the disease later in life probably have an
innate heightened vulnerability to it.
``The evidence is powerful (indicating that) this is a disease due to
something in the environment,'' Langston said. ''There is a widespread
feeling, if we have a shot of finding a cause of any neurodegenerative
disease, it is going to be Parkinson's.''
He said the first strong evidence that Parkinson's could be triggered
by something in the environment came in the 1980s, when a batch
of tainted synthetic heroin was discovered to be causing Parkinson's
symptoms in young addicts.
And studies have found that smoking and coffee--usually assumed
to be detrimental to good health--may actually have a protective effect
against the disease.
More recently, a 1999 study looking at identical twins with Parkinson's
disease found no evidence that genetic factors played a strong role in
the disease in patients older than 50.
At the meeting, researchers presented experimental evidence showing
that common pesticides, herbicides and fungicides may have a harmful
affect on the dopamine-producing nerve cells in the brain, which are
impaired in Parkinson's.
There is strong evidence that pesticides play a role in Parkinson's,
said Webster Ross, a professor of medicine at the University of Hawaii.
He cited a study by Kaiser Permanente in California that found using
pesticides in the home increased a person's risk of developing the
disease by 70%.
J. Timothy Greenamyre, a professor of neurology at Emory University
in Atlanta, Georgia, presented findings on the effect of the common
garden pesticide rotenone on rat brains. Rotenone appeared to cause
cell damage and even neuron death in the rats.
In another animal study, Dr. Deborah Cory-Slechta, head of environmental
medicine at the University of Rochester, gave mice a common herbicide
called paraquat, a fungicide called maneb, or a combination of the two.
Both chemicals are used widely on crops such as fruits, vegetables and
cotton, she said.
The mice who received the two chemicals lost around 40% of their
motor ability, she reported. This loss of ability was sustained when
Cory-Slechta examined the mice 3 months later. The older mice also
seemed more vulnerable to the effect of the two chemicals than
younger mice, she noted.
She also presented preliminary findings that mice exposed to the
chemicals early in life showed more loss of motor activity when
``These effects are irreversible, age-related, and may be produced by
developmental exposure,'' Cory-Slechta said. ``These findings have
enormous implications for human health.''