Data Synthesis And Statistical Analysis
Meta-analysis of results will be considered by investigating heterogeneity among animal and human studies, separately. It is common, though, that environmental health studies have some differences regarding outcome assessments and exposure definitions that could be an obstacle to formal statistical meta-analysis . The heterogeneity associated with pooled effect estimates will be assessed with the use of a 2 test and the I2 statistic . Heterogeneity will be classified as follows: 0 to 40% 30 to 60% 50 to 90% and 75 to 100% .
Statistical analysis will be conducted using the Comprehensive Meta-Analysis STATA software . If considerable heterogeneity is detected among studies, meta-analysis will not be indicated and results will only be presented in tables or in a narrative synthesis. However, if heterogeneity does not exceed 75%, we will use random effects meta-analysis , which is a more conservative approach of pooling the results. In this case, the measure of association will be presented as odds ratios and mean difference, both with a 95% confidence interval , for studies with dichotomous and continuous data, respectively .
Exposure To Pesticides In The Military
Agent Orange was an herbicide that US troops sprayed in Vietnam from 1961-1971 to kill trees and crops that provided protection and food to the rival army. It is a mixture of two chemicals: 2,4-Dichlorophenoxyacetic acid and 2,4,5-Trichlorophenoxyacetic acid. Agent Orange was also contaminated with Dioxin, a chemical even more damaging than Agent Orange itself, since it is very long-lasting.
The effects of Agent Orange on both the Vietnamese population and on American soldiers has been studied extensively, but with much variability in the results. Birth defects have been attributed to Agent Orange exposure, as well as multiple types of cancer.
With the understanding that the Veteran community served selflessly on behalf of the American people and therefore deserve the protection and support of the American government, the Agent Orange Act was passed in 1991, allowing the Department of Veteran Affairs to declare certain conditions presumptive to exposure to Agent Orange, even if the scientific data associating Agent Orange with that condition was not airtight.
The list of conditions has grown over the years, and in 2010, PD was added. Read here about how veterans who may have been exposed to Agent Orange and have subsequently developed PD are eligible for VA healthcare and disability compensation. APDA offers a free booklet specifically for veterans to help them find the care and support they need.
Industrial Chemicals Pesticides And Parkinsons
Since 1982, there has been increasing evidence connecting industrial chemicals to Parkinsons, but reasons to suspect this association stretch back hundreds of years.
InEnding Parkinsons Disease, authors Ray Dorsey, Todd Sherer, Michael Okun, and Bastiaan Bloem write that the first modern description of Parkinsons,An Essay on the Shaking Palsy, was published in London in 1817, a time of severe pollution. The authors argue that this pollution, caused by the citys rapid industrialization, contributed to James Parkinsons recognition of the symptoms now associated with Parkinsons. To support this idea, the authors ofEnding Parkinsons Diseasenote that the modern nations undergoing the most rapid industrialization are also experiencing the fastest increases in the incidence of Parkinsons. The authors also observe that since the Netherlands banned certain chemicals associated with Parkinsons, rates of Parkinsons have dropped in that area. Moreover,a recent study found a significant association between Parkinsons and long-term exposure to air pollution.
In recent years, researchers have made significant progress in understanding how industrial chemicals increase a persons risk of developing Parkinsons. This progress has led to legal action, including civil lawsuits and legislation recently proposed in the US Congress,The National Plan to End Parkinsons Act.
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Which Pesticides Increase Risk
Pesticides are a broad group of chemicals that are structurally and functionally diverse, they have different actions and potential toxicities. As such, the broad brush approach of previous research which looked for the association between Parkinsons and a variety of chemicals used in agriculture often fails to identify individual chemicals which increase risk.
The chemical with the strongest association is the herbicide paraquat, which has been reported to cause a 2.5 fold increase in the odds of getting Parkinsons. And in the lab, when combined with a chemical fungicide, called maneb, researchers have discovered that exposure may active a toxic inflammatory response, lead to the formation of damaging types alpha-synuclein protein, and cause the loss of dopamine-producing brain cells.
But caution should be taken before suggesting that paraquat can cause Parkinsons directly as a more recent meta-analysis states that the evidence so far cannot fully support a causal link between this chemical and Parkinsons.
Despite this, many countries and the whole of the EU have already banned paraquat, but not for its connection to Parkinsons. The chemical is acutely toxic when inhaled or comes into contact with the skin. In other countries, where it has not been banned, restrictive use measures have been established such as limiting its concentration in formulated products and only allowing licensed mixers and ground applicators to manipulate it.
Pesticides Not Only Linked To Parkinsons Disease Development But Accelerating Disease Symptoms
Exposure to certain pesticides among individuals diagnosed with Parkinsons disease can increase the risk of symptom progression. According to a study published in Science of the Total Environment, nearly 20 percent of pesticides associated with the onset of PD also increase the risk of faster decline in motor and non-motor function. Several studies find exposure to chemical toxicants, like pesticides, has neurotoxic effects or exacerbates preexisting chemical damage to the nervous system. Past studies suggest neurological damage from oxidative stress, cell dysfunction, and synapse impairment, among others, can increase the incidence of PD following pesticide exposure. Despite the association between PD onset via pesticide exposure patterns, few epidemiologic studies examine the influence pesticides have on worsening motor and non-motor symptoms in PD.
All unattributed positions and opinions in this piece are those of Beyond Pesticides.
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A Discussion Of How Environmental Factors Such As Pesticides May Affect Your Risk Of Parkinsons Disease
During my recent interview on Wisconsin Public Radio, many of the callers asked questions related to environmental risks of Parkinsons disease , specifically, exposures related to farming. Those calls prompted me to delve further into this complicated and murky topic.
Before we start discussing specific factors in the environment that may increase risk of PD, lets understand some basic ground rules that will help put this topic in perspective
With that background, let us begin.
Environmental Toxins And Parkinsons Disease
Parkinsons disease is said to be because of the loss of dopamine-releasing nerve cells in a small, central part of the brain called the substantia nigra. The substantia nigra produces dopamine, which helps coordinate movement in our body.
But when nigral nerve cells are impaired, less dopamine is released and motor function is affected. And thats when hallmark Parkinsons symptoms including tremors, difficulty balancing, and slowed movement start to set in.
Several studies have suggested that environmental toxicants including pesticides, herbicides, and other pollutants are linked to an increased risk of developing Parkinsons disease.
Heres how these chemicals are said to play a role in the development of the neurological disorder:
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Are People That Use Pesticides More Likely To Get Parkinsons
In occupational terms, there is more limited research. The most relevant evidence comes in the form of a recent systematic review and meta-analysis, which has identified at least a 50% increase in risk with occupational exposure to pesticides.
We know that Parkinsons affects more men than women, and occupational exposures to pesticides and chemicals is often listed as just one of the reasons for this imbalance. However, not everyone who is exposed to risk factors for Parkinsons go on to develop the condition.
But research in the news may help to explain why.
This study used stem cells, some of which carried a mutation in the alpha-synuclein gene, and used them to make dopamine producing brain cells in the lab. They then exposed these new brain cells to paraquat and maneb, or rotenone to assess what effect these chemicals had.
The team, led by Professor Ryan, discovered that the pesticides altered the way mitochondria move around, and believe this could affect the energy levels of the cell. And we already know that the dopamine producing brain cells that are lost in Parkinsons are particularly sensitive to problems with mitochondria.
But more importantly, the cells that contained genetic changes were more affected by the pesticides. This highlights that our genetic makeup likely plays a huge role in how susceptible we are to toxin exposure in our environment, and may help to explain why most people exposed to these chemicals do not go on to develop Parkinsons.
Specific Pesticides And Their Link To Pd
The evidence that pesticide use is associated with an increased risk in PD, begs the question are there specific pesticides that are most concerning? When data is collected on this topic in large populations, often the participants in the study are unaware of which specific pesticide exposures they have had. This makes it difficult to determine which pesticides to avoid.
Some studies however were able to investigate the risks of specific chemicals. A recent review summarized the current state of knowledge on this topic. The chemical with the most data linking it to an increased PD risk is paraquat, with exposure associated with a 2-3 fold increased PD risk over the general population.
One particularly comprehensive study investigated exposure to 31 pesticides and their association with PD risk. From that data emerged paraquat and rotenone as the two most concerning pesticides.
- Paraquats mechanism of action is the production of reactive oxygen species, intracellular molecules that cause oxidative stress and damage cells.
- Rotenones mechanism of action is disruption of the mitochondria, the component of the cell that creates energy for cell survival.
Interestingly, both mitochondrial dysfunction and oxidative stress are common themes in our general understanding of what causes death of nerve cells in PD.
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Paraquat Lawsuits Can Be Filed Decades After The Plaintiffs Exposure
If you were recently diagnosed with Parkinsons disease that may be related to paraquat, you can still file a paraquat lawsuit today, even if your exposure to Paraquat occurs years or even decades ago. All states have a statute of limitations that imposes a deadline for filing a civil tort action for things such as product liability. The applicable statute of limitations period for a tort claim ranges from 1 to 7 years depending on the state.
The applicable SOL period does not begin to run, however, until the plaintiff either knew or had reason to know that they had a claim. For a paraquat lawsuit, this means that the SOL period would not begin to run until the plaintiff knew or should have known that they had Parkinsons disease and that it might have been caused by exposure to paraquat.
The connection between paraquat exposure and Parkinsons disease is something that a reasonable person would not be expected to know. This is particularly true because the companies that made and sold paraquat deliberately failed to warn about the link between paraquat and Parkinsons. Most of the plaintiffs in the Paraquat and Parkinsons disease litigation are bringing their claims based on exposure that occurred a very long time ago.
Who Gets Parkinsons Disease
Globally, its estimated 0.3% of adults over 40 develop Parkinsons disease. Some populations are more likely to develop this condition.
- Age: Aging increases the chances of developing this condition. While seen in less than 1% of those aged 45 to 54, the prevalence rises to 4% of people assigned male at birth and 2% of those assigned female at birth who are age 85 or older.
- Sex: Across global populations, those assigned male at birth are twice as likely as those assigned female to develop Parkinsons disease.
- Ethnicity: Certain ethnicities and races may be more prone to develop Parkinsons disease. Ashkenazi Jews are susceptible to a genetic form of the condition. Also, studies have found elevated rates among Inuit, Alaska Native, and Native American populations.
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So How Worried Should We Be About Pesticides
Long term exposure to pesticides may increase risk of Parkinsons, but you might still be wondering by how much. Often factors that increase risk are presented as a percentage or a fold increase, for instance in this post we quote research that suggests the risk of Parkinsons with environmental exposure to pesticides is increase by at least 50%. But what does that mean in real terms?
Working these statistics out is complex and requires a large amount of data and specialist skills, but for the purpose of understanding how much a 50% increase in risk really matters, I am going to do something a lot simpler.
Well if we use the latest stats that lifetime risk of Parkinsons is around 1 in 37, a 50% increase would put this number at 1.5 in 37, or around 1 in 25. So still, with exposure to pesticides, risk of Parkinsons is relatively low.
We are still learning about how environmental factors affect all aspects of our health, but research like this plays a powerful role in making our environment safer and also improving our understanding of what is happening in conditions like Parkinsons so we can develop new and better treatments.
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Occupational Dermal Exposures Effect On Industry Workers
The Center for Disease Control and Prevention released a study indicating that more than 13 million United States workers across all different industry sectors are believed to be currently at risk of exposure to harmful chemicals via skin absorption. The study mentions that occupational skin exposure may result in the contraction of a wide variety of diseases, which could negatively impact your health and ability to work. These changes could place a significant economic strain on you or your family due to loss of health and the ability to perform tasks required for your line of work.
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Can Parkinsons Disease Be Prevented
It is not possible to prevent Parkinsons disease, but some believe that lifelong healthy habits may reduce ones risk of developing the condition. Some medications may also relieve some of its symptoms.
In some PD patients, particularly those who are at the late stage of the disease, surgery may be an option to help improve symptoms.
Some experts also advise doing preventive measures such as wearing gloves and other protective equipment when applying pesticides as it may help protect you against the disease.
Parkinsons And Occupational Pesticides
A 2012 review of research from Belgiums Catholic University of Louvain confirmed that Parkinsons disease is linked to occupational exposure to pesticides.
The researchers, working with the Louvain Center for Toxicology and Applied Pharmacology, analyzed studies between 1985 and 2011 that looked at pesticide exposure by workers who handled pesticides. These included farm workers who sprayed pesticides.
The research found that those who handled pesticides were significantly more likely to contract Parkinsons disease. In four studies, where the Parkinsons diagnoses were confirmed by neurologists, those handling pesticides had an average of over two-and-a-half times the risk of contracting Parkinsons disease. The increased risk ranged from 46% higher to almost four-and-a-half times higher among the workers.
Three cohort studies, which followed larger populations and compared them to the general population, concluded that workers handling pesticides had close to twice the risk of contracting Parkinsons disease than the rest of the population.
One of these cohort studies showed workers handling pesticides had almost three times the rate of contracting Parkinsons disease.
Their meta-analysis found that all twelve studies individually and combined, established a link between pesticide exposure and Parkinsons disease.
The researchers concluded:
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What Is Parkinsons Disease
Parkinsons disease is a movement disorder in which the nerve cells that transmit messages from your brain and spinal cord to your muscles become damaged. That damage results in progressively worsening motor function and symptoms such as:
- Tremors in your arms, legs, hands, and face
- Slowed bodily movements
- Difficulties with balance, coordination, and speaking
- Stiffness in your arms and legs
- Nonmotor symptoms like depression, fatigue, and cognitive impairment
These symptoms are caused by damage and destruction to dopamine neurons in a persons brain and spinal cord a process called neurodegeneration. However, its unclear exactly why this cell damage happens in people with PD.
Assessment Of Pesticide Exposure To Specific Active Ingredients
The French crop-exposure matrix PESTIMAT was used to assess exposure to some active ingredients in pesticide users of the AGRICAN cohort. This matrix was built to reconstitute pesticide use in France since 1950 in the main crops. For a given crop and a given active ingredient, annual exposure parameters were assessed by a combination of information from six sources about pesticide registration, sales and recommended use.
In the present analyses, we explored associations with some active ingredients used in French crops, which have been associated with PD in previous studies: dithiocarbamate fungicides , bipyridyle herbicides and the insecticide rotenone. None of these substances was used on livestock .
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American Farmers Pursue Syngenta Over Herbicides Link To Parkinsons Disease
The Swiss-based multinational has already set aside $187.5 million to settle legal cases filed by farmers exposed to paraquat. But the total bill could run into billions as lawsuits pile up.
Swissinfo.chs India specialist covers a wide range of issues from bilateral relations to Bollywood. He also knows a thing or two about Swiss watchmaking and is partial to the French-speaking part of Switzerland.
American farmer Doug Holliday has helped feed the nation for decades, growing corn and soybeans and raising cattle on thousands of acres of land outside Greenfield, a rural city of some 2,000 people in the midwestern state of Iowa.
He has joined hundreds of farmers across the United States who have filed product liability lawsuits against the company over its failure to warn them that its top-selling herbicide, paraquat, is linked to serious health problems including Parkinsons disease. Farmers exposed to the toxic chemical, including many who have already developed the debilitating and incurable brain disorder, are also seeking financial compensation for non-economic and economic losses such as medical costs and loss of income.
Not knowing any of this I used paraquat and sprayed it myself on a large farm in the 1990s, Holliday told SWI swissinfo.ch in a telephone interview. I physically handled it and had to pour it multiple times into the sprayer as it was only sold in 2.5-gallon jugs.