The risk of developing Parkinson’s disease is increased by exposure to pesticides, a study has found.

People exposed to low levels of pesticides had a 13 per cent higher risk of developing the disease, and those exposed to high levels a 41 per cent greater risk, researchers from Aberdeen University found.

The researchers compared the lifetime experiences of almost 1,000 Parkinson’s sufferers with almost 2,000 unaffected people in Scotland, Italy, Sweden, Romania and Malta. The method did not establish which pesticides the sufferers had been exposed to, as most of them could not provide such information.

Being knocked out in a boxing ring or suffering an accident that causes unconsciousness is even likelier to bring on Parkinson’s. Those who had suffered a single knockout had a 35 per cent greater chance of developing the disease, while those who had been knocked out more than once more than doubled their risk.

The boxer Muhammad Ali, three times heavyweight champion of the world, suffers from Parkinson’s syndrome — a related condition — which most medical experts believe was caused by his experiences in the ring.

The latest study, by the European Commission, aimed to identify factors that can accelerate or cause the disease. The results are published in Occupational and Environmental Medicine. Kieran Breen, director of research and development for the Parkinson’s Disease Society, said that the findings reinforced the belief that the disease was caused by more than one factor.

He said: “The association between pesticides and Parkinson’s has been recognised for some time. The results of this study compound the results of a 2006 study of 147,000 people, conducted by the Harvard School of Public Health, which also found the incidence of Parkinson’s to be slightly higher in people who reported previous exposure to pesticides.”

Georgina Downs, of the UK Pesticides Campaign, said that it was not surprising that study after study linked pesticides to chronic neurological and neurodegenerative diseases. “This study has found that the risk of developing Parkinson’s disease increases according to the level of exposure to pesticides,” she said. “This is highly significant in relation to the long-term exposure of rural residents living near sprayed fields.”

She said that it would be difficult to establish which pesticides were responsible as they are rarely used one at a time.

The European Commission said last year that long-term exposure to pesticides could lead to serious disturbances to the immune system, as well as sexual disorders and cancers.

The disease

— Parkinson’s is a progressive brain condition

— Symptoms include tremors, limb rigidity, slow movement and balance and coordination problems

—These are caused by the loss of dopamine-producing nerve cells in the brain

— Parkinson’s does not in itself kill, but it can hasten death from other causes

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