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Studies back Parkinson’s,
pesticides link
Reuters
Monday April 23, 2007
Evidence that pesticides can cause Parkinson’s disease is
stronger than it has ever been after a meeting of experts who have
put together links in animals and people, scientists say.
One study shows that farm workers who used the common weedkiller
paraquat had two to three times the normal risk of Parkinson’s,
a degenerative brain disease that eventually paralyzes patients.
A second study shows that animals exposed to paraquat have a build-up
of a protein called alpha-synuclein in their brains. This protein
has been linked to Parkinson’s in the past.
A third piece of the puzzle shows that this buildup of protein kills
the same brain cells affected in Parkinson’s.
“All of these pieces really look like they are coming together
now,” Dr. William Langston, founder of the non-profit Parkinson’s
Institute, told Reuters.
Langston and colleagues said they were energized by research presented
at the Parkinson’s Disease Environmental Research meeting
in Monterey, California, earlier this month.
Parkinson’s disease, which affects more than 1 million patients
in the United States, is marked by the death of brain cells that
produce dopamine.
Dopamine is a neurotransmitter, or message-carrying chemical, associated
with movement. Drugs can delay symptoms for a while but there is
no good treatment and no cure.
Farm workers are at especially high risk but links to pesticides
have been difficult to document because years usually pass between
a person’s exposure to pesticides and the development of the
disease.
Dr. Beate Ritz of the University of California at Los Angeles and
Dr. Caroline Tanner of the Parkinson’s Institute looked at
80,000 people in Iowa and North Carolina and found farm workers
exposed to paraquat had twice the expected risk of Parkinson’s
over their lifetimes.
Exposure to another pesticide called dieldrin also raised the risk,
the study, funded by the National Institute of Environmental Health
Sciences, found.
A second study found similar effects in farm workers in central
California.
Better documentation
What made the studies especially important was that pesticide exposure
could be carefully documented through records of pesticide purchase,
Langston said. Details will be published in a scientific journal
later.
Dr. Donato Di Monte of the Parkinson’s Institute gave paraquat
to laboratory animals and found it caused a buildup of alpha-synuclein
in the brain that killed the same neurons affected by people with
Parkinson’s disease.
“This increase in alpha-synuclein in the brain could be the
missing link between the exposure to this agent and how this agent
causes the disease,” Di Monte said in a telephone interview.
“Maybe being exposed to paraquat may not be enough to cause
the disease but increases the probability the disease may develop,”
Di Monte said.
Langston and Di Monte said inflammation also could be a factor.
“Give an animal a compound that creates a marked inflammation
response in the body ... and months later the animal loses cells
in same area of the brain that is associated with Parkinson’s,”
Langston said.
“This suggests that systemic inflammation may somehow sensitize
the brain.”
Multiple concussions, which can cause inflammation in the brain,
raise the risk of Parkinson’s, Langston said.
Two other groups of people that have a higher-than-average risk
of Parkinson’s are health workers and teachers.
“At first glance that doesn’t make sense,” Langston
said.
But both do have something in common — frequent exposure
to viruses.
It could be, Langston and Di Monte said, that if a person is exposed
to a pesticide while his or her brain has inflammation, this greatly
raises the risk of Parkinson’s many years later.
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