Risk of Alzheimer's disease and other forms of dementia are associated with long-term exposure to pesticides according to a study released Thursday.
Workers "directly exposed" to bug and weed killers while toiling in the prestigious vineyards of Bordeaux, France were five times more likely to score less well on a battery of neurological tests than those with minimal or no exposure, the study found.
As revealing, this high-exposure group was twice as likely to register a significantly sharp drop in a key test -- frequently used to diagnose dementia -- repeated four years after the initial examination.
The drop "is particularly striking in view of the short duration of follow up and the relatively young age of the participants," mostly in their late 40s or 50s, the authors said.
The findings, published in the peer-reviewed journal Occupational and Environmental Medicine, add to a growing body of evidence suggesting that chronic use of pesticides in agriculture boosts the risk of neurological disorders.
France has the highest use of insecticides and herbicides in Europe, and the fourth highest worldwide after the United States, Japan and Brazil.
More than 800,000 people in France are exposed in the agriculture sector, as were another 800,000 who are now retired.
Worldwide the number of labourers who work regularly with pesticides is counted in the tens, if not the hundreds, of millions.
In the Bordeaux study, led by Isabelle Baldi of The French Institute for Public Health, Epidemiology and Development, 614 workers were enrolled in 1997 and 1998 and re-evaluated four or five years later.
On both occasions they completed a detailed questionnaire on their work history, along with nine tests designed to measure memory and recall, language retrieval, verbal skills and reaction times.
The subjects were divided into four groups depending on their level of exposure to pesticides over the previous 20 years or longer, ranging from "directly exposed" to "not exposed".
"The mild impairment we observed raises the question of the potentially higher risks of injury in this [exposed] population, and also of the possible evolution toward neurodegenerative diseases such as Alzheimer's or other dementias," the researchers concluded.
The same cohort is undergoing a third evaluation, 12 years after the baseline examination. Results will be published in 2012 or 2013.
"This time lag should enable us to better understand cognitive impairment and its evolution, and observe the first cases of Alzheimer's disease among a population close to 65 years of age," the researchers said in a companion briefing paper.