At meetings for people with Parkinson's there seems to be little or no discussion of the causes of PD. WHY?! Parkinson's KILLS you. You want to know what to warn your children, and everybody else, to avoid. You don't want others to get this currently incurable, unpleasant illness. Reading the available literature or searching the internet shows the following risk factors
Well no-one has yet discovered an anti-aging cream that works so there is not much hope in finding a cure there then! We can try to avoid head trauma and easily take precautions such as wearing helmets.
There is a lot of research into the genetic side of PD and Parkinsonism, however genetics only plays a role in a small number of cases of PD (~5 to 10%). Genetics can be studied in detail in a laboratory and gives more definitive results hence why a lot of research is being ploughed into this area. That said, studying the rarer genetic cases may give insight into the more common forms of Parkinsons.
That leaves environmental factors, e.g. Pesticides or other toxins.
Many, many studies of exposure to pesticides clearly suggest that they often have a causal role in Parkinson's Disease (PD). These often date from the 1990s and onwards, yet the Parkinson's Disease Foundation (PDF) states "We do not yet know what causes Parkinson's disease (PD) to develop in most people." [PDF Website Oct 2008].
In statistics, a meta-analysis combines the results of several studies that address a set of related research hypotheses. Meta-analysis is widely used in epidemiology and evidence-based medicine today.
Odds Ratio? The Odds Ratio (O R) is defined as the ratio of the odds of an event occurring in one group to the odds of it occurring in another group, or to a sample-based estimate of that ratio.
These include a Environmental Risk Factors and Parkinson's Disease: A Metaanalysis by Anumeet Priyadarshia, Sadik A. Khuderb, a, 1, Eric A. Schaubb, a and Snigdha S. Priyadarshib, which gave a combined Odds Ratio for pesticides exposure was 1.85(95% CI 1.31-2.60) for all studies, and 2.16(95% CI 1.95-2.39) for studies done in United States. The second largest OR in the study (the largest was for rural residence of 1.56 [95% confidence interval (95% CI) 1.18-2.07] for all the studies, and 2.17(95% CI 1.54-3.06) for studies performed in United States).
Researchers at the Harvard School of Public Health undertook a prospective study to examine possible links between chronic low-dose exposure to pesticides and Parkinson's Disease.They found that "the significant association between pesticide exposure and Parkinson's disease among individuals who are not farmers is most likely explained by use of pesticides at home or in gardening".
Research by Alberto Ascherio in the Annals of Neurology in 2006 found that "Exposure to pesticides was reported by 7,864 participants (5.7%), including 1,956 farmers, ranchers, or fishermen. Individuals exposed to pesticides had a 70% higher incidence of PD than those not exposed (adjusted relative risk, 1.7; 95% confidence interval, 1.2-2.3; p = 0.002). The relative risk for pesticide exposure was similar in farmers and nonfarmers. No relation was found between risk for PD and exposure to asbestos, chemical/acids/solvents, coal or stone dust, or eight other occupational exposures". This was before the denials of the APDA (American Parkison Disease Association) and PDF!
So it is clear that pesticides are a major cause of PD. There have been many studies, carefully meta analysed + feasible mechanisms: eg insect neurons destroyed by the same pesticide-damage that kills human neurons or rat neurons. Yet, in the US, very few people know that pesticides are a major cause and, it seems, there is no good system to ban those pesticides that should be banned....and insufficient warnings to gardeners and agricultural workers. BUT ..the APDA is still in denial about pesticides: a leaflet for its 2008 'Walk-a-thon' states "the ultimate goals of discovering the cause and cure remain elusive". Causes are known...A cure is not! Don't they read?!