Gardeners who use pesticides could be at an increased risk of developing Parkinson's disease, according to media reports.
Parkinson's affects 120,000 Britons annually, with 10,000 new cases diagnosed each year.
Scottish researchers found that exposure to high levels of pesticide increased the risk of Parkinson's by 41 per cent, while low levels raised it by 13 per cent.
But the study did not establish which pesticides the participants had been exposed to because most were unable to provide such information.
The researchers concluded that the findings do not prove that pesticides cause Parkinson's.
They also found that the likelihood of developing the disease increased with higher frequency of being knocked unconscious.
What is the research?
The reports are based on Scottish research that investigated the potential association of environmental risk factors with the development of Parkinson's.
For the study, the researchers compared the lifetime experiences of 959 Parkinson's sufferers, average age of 69, who were selected using records of patients attending neurology and medicine for the elderly outpatient clinics, with a group of 1,989 unaffected controls, matched for age and gender.
A history of lifetime employment was gathered at the beginning of the study, along with data relating to the duration and likely intensity of occupational and hobby exposure to target agents such as pesticides, iron and copper.
Exposure to each target material was categorised as zero, low, medium or high.
History of having been knocked unconscious and family history of Parkinson's was also recorded, as well as smoking, alcohol and educational histories.
An increased risk of Parkinson's was found with exposure to solvents, pesticides, iron and copper, but the risk was only statistically significant for pesticides.
People exposed to low levels of pesticides had a 13 per cent higher risk of developing the disease than those who had never been exposed, and those exposed to high levels a 41 per cent greater risk.
People who had suffered a single knockout had a 35 per cent greater chance of developing the disease, while those who had been knocked unconscious more than once were two-and-a-half times more likely than normal to develop Parkinson's.
What do the researchers say?
Lead researcher Dr Findlay Dick, from the department of environmental and occupational medicine at Aberdeen University, said this was the first study to show an exposure-response relationship between pesticides and Parkinson's.
'Although we found an association with pesticide use and an increased risk of Parkinson's, the overall risk of developing the disease is still small.
'Even those who were exposed to the highest levels of pesticide still only had a 41 per cent increased risk of Parkinson's.
'The pesticides themselves are diverse and not all of them will be associated with an increased risk of Parkinson's,' he said.
'There are also other factors involved in Parkinson's that need to be taken into consideration such as genetics and diet,' he said.
Dr Dick added that further research was required to understand the link to Parkinson's.
'There are a number of potential pathways that may explain the link.
Pesticides may be inhibiting enzyme pathways in the mitochondria. They may also have an effect on dopaminergic neurones.
'But we are hindered in our studies as there are no long-term markers of pesticide use that we can examine.'
What other researchers say?
Dr Kieran Breen, director of research and development for the charity Parkinson's Disease Society, said that the findings of the study fitted in with previous research which had shown an association between pesticides and the development of Parkinson's disease.
'The important finding from this study is confirmation that Parkinson's is not caused by any one factor, but instead a combination of genetic susceptibility and environmental factors,' Dr Breen said.
'The study does give some indication of potential risk factors, however this would need to be repeated in other study groups to confirm the findings,' he said.Informing patients
- People exposed to low levels of pesticides have a 13 per cent higher risk of Parkinson's, and those exposed to high levels a 41 per cent greater risk.
- The study did not identify which pesticides were to blame for the risk.
- Research is required to understand how pesticides could increase the risk of Parkinson's.