The New Scientist JUne 26, 2006


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



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)

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