A team from Harvard School of Public Health found that people who said in 1992 that they had been in contact with pesticides were 70 per cent more likely to develop Parkinson’s within the next 10 years.
When people are questioned after a diagnosis has been made, their answers are often unreliable. They may have heard suggestions of such a link, which colours their recollection of previous exposure, according to the Times Exposure.
A team led by Alberto Ascherio used data from a study of the link between diet and cancer, begun in 1992. Of the volunteers who filled in the original data, 143,325 responded in 2001 to a follow-up survey to see how they had fared.
Although the causes of Parkinson's are not well understood, it has long been suspected that environmental factors play a large role. Animal studies have shown that chemical compounds commonly used as pesticides can cause a degeneration of dopamine-producing neurons. In Parkinson's, a shortage of dopamine causes the disease's characteristic motor abnormalities, including muscle tremors and muscle rigidity, Scientific American reports.