The New
Scientist JUne 26, 2006
http://www.newscientist.com/article/dn9408-pesticide-exposure-raises-risk-of-parkinsons.html
Pesticide exposure
raises risk of Parkinson's
By Roxanne
Khamsi
Exposure to pesticides
- even at relatively low levels - may increase
an individual's risk of
developing Parkinson's disease by 70%,
according to a study of
more than 140,000 people. Researchers say
that the findings
strengthen the hypothesis that such chemicals
somehow promote the
development of the disease.
In recent years,
experts have identified genetic mutations that
apparently predispose
people to develop Parkinson's. But some mystery
remains because not
everyone with the mutations will get the
devastating
neurological disorder, which is characterised by
rigid
and slow movement or
other problems with body coordination. Likewise,
Parkinson's can develop
in individuals with no known genetic
predisposition.
As a result, many
scientists maintain that environmental factors
ultimately trigger the
development of Parkinson's
disease.
The idea that
pesticides may be to blame has now received a
boost
from the first
large-scale, prospective study to examine this
possible link. Alberto
Ascherio of the Harvard School of Public
Health in Boston,
Massachusetts, US, and colleagues looked at data
from roughly 143,000
people involved in a cancer and diet study, of
whom 413 were diagnosed
with Parkinson's disease in the
1990s.
Toxin
exposure
In 1982 these
volunteers each completed an initial
questionnaire,
providing information
about their occupation and levels of exposure
to various
toxins.
Ascherio and colleagues
found that those who reported exposure to
pesticides had a 70%
greater risk of developing Parkinson's disease
than those who said
they had no such exposure. But exposure to other
toxic compounds - such
as asbestos and formaldehyde - did not
increase their chances
of acquiring the illness.
Ascherio stresses that
the absolute risk of developing Parkinson's is
low. So while about 2%
of the population as a whole may be at risk of
developing the disease,
exposure to pesticides might increase this
risk to little more
than 3%.
Of the 413 patients
with Parkinson's disease, 43 reported exposure
to
pesticides. But
surprisingly the study found that farmers - many
of
whom presumably had
high levels of exposure - and non-farmers shared
a similarly increased
risk. This contradicts a previous, smaller
study reporting that
risk rises with exposure levels (see Exposure to
pesticides can cause
Parkinson's).
Garden
pesticides
Ascherio suggests that
non-farmers may have encountered pesticides
while gardening. "Maybe
the pesticides used in agriculture are not
the most harmful," he
speculates. He regrets that the initial
questionnaire did not
include more details about the type, duration
and intensity of
pesticide exposure.
Experts stress that
many people unknowingly consume pesticides on a
daily basis. "If you
analyse the fruit and vegetables we eat, they're
full of chemicals,"
says Serge Przedborski of Columbia University in
New York, US. He adds
that traces found in such foods can accumulate
over a lifetime to
potentially harmful levels.
Przedborski describes
the new study as "excellent" because
researchers collected
data about pesticide exposure years before
participants developed
Parkinson's disease, ruling out potential
bias. But he notes that
it does not prove that pesticides are the
main cause of
Parkinson's disease.
Moreover, Przedborski
explains that because the initial questionnaire
did not ask about
specific pesticides, we are no closer to knowing
which particular
chemicals are the culprits. "In reality, we have
no
idea," he
says.
Journal reference:
Annals of Neurology
(DOI:10.1002/ana.20904)