GARDENERS and farmers who spray plants with pesticides could be increasing their risk of contracting Parkinson’s disease, research has shown. The finding has emerged from one of the largest epidemiological studies conducted into the effects of such chemicals.

In the study researchers followed the health of 143,000 people since 1982, trying to pick out the factors that lead to diseases such as cancer and Parkinson’s. They found that people regularly exposed to pesticides, even in relatively small doses, had a 70% higher incidence of Parkinson’s disease compared with those who had not been exposed.

They also found that gardeners who used such chemicals were at just as much risk as farm workers who used them as part of their job.

“The findings support the idea that exposure to pesticides is a risk factor for Parkinson’s disease,” said Professor Alberto Ascherio, of the Harvard School of Public Health, who led the study.

Parkinson’s is a brain disease that afflicts about 150,000 Britons, with nearly 10,000 new cases a year. Symptoms include involuntary tremors, muscular rigidity or stiffness and slowness of movement that can make walking, talking and writing difficult, if not impossible.

Scientists have suspected a link between pesticides and Parkinson’s since 1983 when Californian drug addicts were diagnosed with the disease after taking impure drugs. The toxin that damaged their brains had a molecular structure similar to Paraquat, a common pesticide.

Since then epidemiological studies have hinted at links between such chemicals and the disease but few have been large enough to extract meaningful figures. The latest research, published in the Annals of Neurology, is big enough to get around that problem but also raises new questions, especially over which particular pesticides might be causing this effect.

“A similar increase in risk was observed among people who were exposed because of their occupation, such as farmers, as among people not occupationally exposed, suggesting home or garden use is equally deleterious,” said Ascherio.

In Britain 31,000 tons of pesticides are applied to gardens and farms each year. Cereal crops are sprayed five or six times in a season while potatoes can get 12 dousings and fruit crops such as apples up to 18.

The Crop Protection Association, which represents manufacturers, says pesticides are vital to farming and gardeners. Peter Sanguinetti, CPA chief executive, said: “We are not responsible for the science relating to pesticides. We are given rules by the government and we comply with them.”

Georgina Downs, of the UK Pesticides Campaign, said: “Many pesticides are designed to be toxic to animals’ nervous systems so a link with Parkinson’s is not surprising.”

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