“What exactly causes Parkinson’s disease is far from figured out. But a clue has been lurking in cornfields for years,” begins a 2014 Scientific American article. “Farmers are more prone to Parkinson’s than the general population. And pesticides could be to blame.”
Over a decade of evidence shows a clear association between pesticide exposure and a higher risk for the second most common neurodegenerative disease, after Alzheimer’s. A study published in Neurology proposes a potential mechanism by which at least some pesticides might contribute to Parkinson’s.
When nigral neurons die, motor function goes haywire and the classic symptoms set in, including namely tremors, slowed movements, and rigidity.
In 2000, a meta-analysis linked confirmed and presumed pesticide exposure with increased risk of Parkinson’s. Subsequent work supported this connection, including a large 2006 study that followed patients for nine years. The patients exposed to pesticides had a 70% higher incidence of Parkinson’s when the study ended; the risk was the same for exposed farmers and exposed non-farmers.
In 2011 researchers analyzed individuals working and living in the California Central Valley who were exposed to 3 specific pesticides (ziram, maneb, and paraquat). Contact occurred through air contamination at both the workplace and those residences within 500 meters of pesticide application. They found an 80% increase in Parkinson’s disease development (especially among those younger at onset of symptoms) when exposed to a combination of 2 of the 3 pesticides. The risk was highest when ambient exposure occurred at both the residence and place of work.
Another study suggested a potential risk for Parkinson’s disease by ambient pesticide exposure among those living downwind from a golf course.
Heptachlor epoxide, a pesticide used on pineapples, that was present in milk in the early 1980s may be linked to signs of Parkinson’s disease that are showing up in people today, according to a 2015 study. The researchers looked at Japanese-American men in Hawaii, where the pesticide was frequently used, and found that those who drank more than two cups of milk daily at the start of the study had 40 percent fewer brain cells in an area of the brain called the substantia nigra 30 years later, on average, compared with similar men who drank less than two cups of milk per day.
High levels of the pesticide were found in the milk supply in the early 1980s in Hawaii, where the chemical was used for insect control in the pineapple industry. The commercial sale of the pesticide in agriculture was banned in the United States by 1988.
A 2016 review, Glyphosate pathways to modern disease V: Amino acid analogue of glycine in diverse proteins, conducted by a scientist at Massachusetts Institute of Technology, found glyphosate (Roundup) acts as a glycine analogue that incorporates into peptides during protein synthesis. In this process, it alters a number of proteins that depend on conserved glycine for proper function. Glyphosate substitution for glycine correlates with several diseases, including diabetes, obesity, asthma, Alzheimer’s disease, amyotrophic lateral sclerosis (ALS), and Parkinson’s disease, among others.
According to the study, the consequences of this process can lead to impaired fatty acid release leading to obesity, impaired insulin receptor response leading to diabetes, impaired one-carbon metabolism leading to neural tube defects and autism, impaired cell cycle control during DNA synthesis, and disregulated phosphorylation cascades leading to cancer, lung disorders, and autoimmune diseases.
In June a delegation of independent scientists including the study’s authors, presented their findings at a Congressional briefing sponsored by U.S Representative Ted Lieu, urging lawmakers to call on the EPA to ban RoundUp, Monsanto’s flagship herbicide.
A review in the medical journal Lancet Neurology in November noted: Increased risk of Parkinson’s disease has been associated with exposure to pesticides, consumption of dairy products, history of melanoma, and traumatic brain injury, whereas a reduced risk has been reported in association with smoking, caffeine consumption, higher serum urate concentrations, physical activity, and use of ibuprofen and other common medications.