A study of almost 500 people newly diagnosed with Parkinson's disease has found that home exposure to pesticides is associated with an increased risk of developing the disease. "This study is the largest yet of newly diagnosed individuals with Parkinson's disease and it is the first study to show a significant association between home pesticide use and the risk of developing Parkinson's disease," said neuroepidemiologist Lorene Nelson, PhD, associate professor of health research and policy. Nelson conducted the study with her colleagues Stephen Van Den Eeden, PhD, from the Kaiser Permanente Medical Care Program of Northern California and Caroline Tanner, MD, PhD, from the Parkinson's Institute in Sunnyvale.
The researchers questioned 496 people who had first been diagnosed with Parkinson's disease in 1994 or 1995 about past use of pesticides. They wanted to know if each patient had handled or applied insecticides in the home or garden, herbicides or weed killers in the garden, or fungicides to control mold or mildew in the home or garden. The researchers asked detailed questions about past pesticide use including when patients first were exposed and how frequently they came into contact with it. The researchers also queried the respondents on lifestyle factors such as cigarette, alcohol and coffee consumption. They then asked the same questions of 541 people without Parkinson's disease who served as age- and gender-matched control subjects.
When the researchers compared the lifetime histories of the patients and the control subjects they found that people who had handled or applied pesticides in the home or garden were more likely to develop Parkinson's disease than those who had not received such exposure. People exposed to in-home insecticides were 70 percent more likely to develop the disease than those who had not been exposed. The average amount of time that people reported being exposed to products in this category was 77 days.
Exposure to garden insecticides carried a 50 percent increased risk of disease. Among herbicide users, risk of developing Parkinson's disease increased as the number of days that people were in contact with herbicides accumulated. Respondents who reported handling or applying those products for up to 30 days were 40 percent more likely to develop disease whereas respondents that reported higher levels of exposure (an average of 160 days) had a 70 percent increased risk of developing Parkinson's disease. Exposure to fungicides was not found to be a risk factor.
Nelson's study is believed to be the first study to specifically examine the link between Parkinson's disease and domestic exposure to pesticides. The researchers announced their findings May 5 at a presentation at the annual meeting of the American Academy of Neurology, in San Diego. According to Nelson, the preliminary results from this study mirror what is already known about the increased risk of Parkinson's disease associated with occupational exposure to both insecticides and herbicides.
Similarly, a previous study by other researchers found increased risk of the disease among hobby gardeners, although pesticide exposure as a possible cause of the increased risk was not investigated. But many more studies are needed before any conclusive statements can be made about the causes of Parkinson's disease, including any possible genetic influences on a person's probability of developing the disease, Nelson cautioned. Damage to nerve cells in a part of the brain called the substantia nigra and subsequent deficiency in the neurotransmitter dopamine leads to the balance and movement difficulties characteristic of Parkinson's disease.
Therefore, people exposed to chemicals that have a particular affinity for this region of the brain may be at particular risk for developing the disease, said Nelson. "Pesticides that contain chemicals that target dopamine-producing neurons in the substantia nigra may cause selective death of those neurons," she said. "If we could understand why these neurons are being killed in certain circumstances we can then try to prevent or treat the disease," she said.
But Nelson also stressed that the results of the study must be interpreted with caution. "No specific guidelines regarding avoidance of pesticides can be given at this time. However, this is an area of public health importance that needs to be pursued with additional studies," said Nelson. The study results also may serve as a reminder that people should read manufacturers' labels and heed the warnings noted, she added.
Funding for the study was provided by the National Institutes of Health.
Rochester NY, (January 27, 2005) - In two companion papers, University of Rochester researchers have identified early environmental risks for Parkinson's disease, a progressive neurological disorder that affects one in every 100 Americans over age 60.
Polychlorinated biphenyls (PCBs), the now-banned lubricants that persists in the environment, disrupt a type of nerve cell that degenerates in the course of the disease.
And Maneb, a fungicide still commonly used on farms, impedes the ability of those same cells to recover from injury. Maneb can persist in soil for up to 75 days after application, and can stay on produce for more than three weeks, even after washing.
The two recent studies - both in the journal NeuroToxicology - add to an increasing body of science that implicates chemical exposures in Parkinson's and other diseases that affect the nervous system.
"You've caught me at an exciting time," said lead investigator Lisa A. Opanashuk, an assistant professor of environmental medicine at UR.
Studies in her laboratory this year will look at more chemical risk factors, including dioxins, heavy metals and other pesticides, she said. Another avenue being explored: how combinations of pesticides may damage the nervous system - research that may lead to better safety guidelines, especially in rural areas.
Scientists have already linked Parkinson's to the pesticide Dieldrin, and have acknowledged genetic factors that increase risk.
Another known risk factor is stress on cells related to aging, which make them less likely to be bathed in oxygen.
The new UR research could lead to early intervention in treating Parkinson's, said Opanashuk. That includes treatment with antioxidants, either as supplements or through direct applications of antioxidants to the brain, using genetic material as a vector.
PCBs are typically associated with the food chain, in particular fish, whose fatty tissue traps the persistent chemical.
But the university will also start to explore how PCBs in the environment can cause harm by being inhaled, said Opanashuk, a four-year UR veteran.
"That's a huge issue of concern," she said of airborne PCBs, "the most prominent avenue of exposure that hasn't been explored."
Dr. David Carpenter, a public health researcher at the State University of New York at Albany, published a study in December that linked PCB-related hazardous waste sites statewide to an increased risk for infectious respiratory disease. Thirteen of the 213 at-risk ZIP codes he identified were in the Rochester area.
Carpenter's contention is similar to that of UR researchers: that PCBs suppress the body's ability to fight off disease.
Both PCBs and Maneb, Opanshuk said, are related to "oxidative stress," which blunts the antioxidant enzymes that fight off disease, at a cellular level.
The PCBs paper was published in the December issue of NeuroToxicology. The one on Maneb has been accepted for the February issue.
UR has a Parkinson's Disease Data and Organizing Center, part of a network of 12 research institutions nationwide, and a Parkinson Study Group.
Suspicions that pesticides could cause Parkinson's disease have been strengthened. The more pesticide you are exposed to, the higher your risk of developing the disease, say investigators who have studied almost 3000 people in five European countries. The results reinforce the need for amateur gardeners and farmers alike to wear protective equipment when spraying pesticides, the team concludes.
"It considerably strengthens the case for pesticides being relevant to occupational risk of Parkinson's disease," says Anthony Seaton of the University of Aberdeen, UK, principal investigator of the Geoparkinson study, which was funded by the European Commission and followed volunteers in Scotland, Italy, Sweden, Romania and Malta. Researchers questioned 767 people with Parkinson's disease and 1989 healthy controls with similar backgrounds about several risk factors associated with the disease, including exposure to pesticides.
People with Parkinson's were more likely to have used pesticides regularly. Users with low exposure such as amateur gardeners were 9 per cent more likely than non-users to develop the disease, and high-exposure users such as farmers were 43 per cent more likely.
David Coggon of the University of Southampton, UK, and chairman of the British government's Advisory Committee on Pesticides, said the study's weakness, acknowledged by the authors, is that it could not identify which pesticides were responsible. "It's possible that just one or two are causing it, but slipped through the regulatory net," says Coggon. It would be more helpful, he adds, for studies to monitor exposure to individual pesticides as and when they are used, rather than relying on people's memories of their usage.
To put the pesticide risks into perspective, Seaton says that the study identified other, much stronger risk factors. Having a family history of the disease increases your risk by 350 per cent, although they found no link between risk of Parkinson's and 18 gene mutations suspected of causing the disease. Being knocked unconscious once raises the risk by 32 per cent, rising to 174 per cent for those who have been knocked out several times.