People with raised levels of a particular pesticide in their blood may have an increased risk of Parkinson's disease, research published yesterday showed.
The findings provide some of the strongest evidence yet linking Parkinson's and pesticide exposure. Scientists believe they could lead to a blood test that would identify potentially susceptible individuals. Those at risk could then be given protective treatment and monitored for early signs of the disease.
Previous studies have found higher than normal levels of organochlorine pesticides such as DDT in the brains of Parkinson's patients. But the new research is the first to highlight a specific pesticide chemical in the blood.
Scientists studied 113 people aged 50 to 89. Fifty had Parkinson's, 43 were healthy, and 20 had Alzheimer's disease.
Tests were carried out on their blood to search for traces of 15 organochlorine pesticides. One chemical, beta-HCH (hexachlorocyclohexane), was unusually likely to be found in the blood of people with Parkinson's.
Beta-HCH was detected in 76% of these samples compared with 40% of the healthy volunteers and 30% of Alzheimer's sufferers.
Blood levels of the chemical were also markedly higher among Parkinson's patients compared with the other groups.
Study leader Professor Dwight German, from the University of Texas Southwestern Medical Center in Dallas, US, said: "There's been a link between pesticide use and Parkinson's disease for a long time, but never a specific pesticide.
"This is particularly important because the disease is not diagnosed until after significant nerve damage has occurred. A test for this risk factor might allow for early detection and protective treatment."
Organochlorines were widely used from the 1950s to the 1970s but are now much more tightly regulated.
They persist in the environment for years without breaking down, dissolve in fats, and are known to damage nerves.
"Much higher levels of the beta-HCH were in the air, water and food chain when the Parkinson's patients were in their 20s and 30s," said Prof German. "Also, the half-life of the pesticide is seven to eight years, so it stays in the body for a long time."
The scientists, who report their findings today in the journal Archives of Neurology, believe pesticide exposure is just one of a number of factors that contribute to Parkinson's.
Evidence suggests some people have a genetic make-up that makes them sensitive to the chemicals. They may not be able to metabolise, or break down, the substances as well as others. This would explain why the Parkinson's patients in the study had raised levels of beta-HCH in their blood.
Another possibility was that beta-HCH was not the harmful agent itself, but acted as a marker for the presence of another damaging chemical.
The scientists wrote: "It is possible that elevated levels of beta-HCH may be a useful clinical measure to identify people who may have an increased risk of PD (Parkinson's disease), particularly when combined with information about genetic polymorphisms in genes that metabolise organochlorine pesticides."
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