For a deep dive into the environmental risk factors of PD, check out our latest Let’s Talk Parkinson’s feature with Beate Ritz, MD, Ph.D., a Professor of Epidemiology and Environmental Health Sciences and Neurology at UCLA.

The relationship between environmental factors and Parkinson’s disease has been largely unknown until recently. With more studies emerging, researchers are beginning to understand the complexities between genetics, environment, and Parkinson’s disease.

PD is primarily a “sporadic disorder,” meaning that it occurs randomly and does not typically have a clear pattern of inheritance in a family. Compare this to “familial disorders,” which suggest a possible genetic component to the disease.

While scientists have discovered several genetic risk factors that may account for rare familial forms of Parkinson’s disease, about 85-90% of cases are sporadic. Understanding the underlying causes of PD means exploring all aspects of its development, especially environmental factors.

Here’s what we know about the environmental risk factors associated with Parkinson’s disease.

Environmental Risk Factors, Explained

A complex interplay of genetic predispositions and environmental exposures influences Parkinson’s disease.

Environmental risk factors are diverse and can vary significantly in their impact on individuals. Additionally, certain genetic makeups may make some people more susceptible to these environmental influences.

Here’s an overview of these risk factors:

Pesticides & Herbicides

Certain chemicals like rotenone, which is used in pesticides, have been shown to cause Parkinson-like symptoms in laboratory animals by interfering with mitochondrial function and increasing oxidative stress. Consumption of well water contaminated with pesticides and heavy metals has also been associated with an increased risk of Parkinson’s disease.

Further, the herbicide paraquat has been linked directly to Parkinson’s and is widely used across the United States despite being banned in 32 countries.

Pesticides may cause neuronal damage by disrupting cellular processes, promoting alpha-synuclein aggregation (a hallmark of PD development), and impairing dopamine function in the brain.

Inhalation, dermal contact, or ingestion can cause exposure, often affecting agricultural workers and those living near farms.

Heavy Metals

Lead, mercury, and manganese are metals that are particularly concerning. Chronic exposure to these metals can damage the nervous system. These metals can accumulate in the brain and disrupt cellular function, leading to the death of dopaminergic neurons.

People working in welding, mining, and battery manufacturing industries may be at higher risk of exposure to these metals.

Solvents

Trichloroethylene (TCE) and perchloroethylene (PERC) are solvents used in degreasing agents and dry-cleaning solutions, respectively, and have been linked to increased PD risk. These solvents may induce changes in the brain that mimic those seen in Parkinson’s disease, including mitochondrial dysfunction and oxidative stress.

Air Pollution

Air pollution potentially increases the risk of developing Parkinson’s disease via neuroinflammation, oxidative stress, and blood-brain barrier disruption.

Inhaled pollutants can directly or indirectly affect the brain, possibly leading to increased aggregation of alpha-synuclein, a protein linked to PD. Additionally, air pollution may cause mitochondrial dysfunction and exert direct neurotoxic effects, contributing to neuronal damage.

Head Injury

Head injuries that cause concussion or loss of consciousness (such as a traumatic brain injury) can lead to chronic inflammation and abnormal protein accumulation in the brain, both of which are associated with PD. Further, multiple head injuries may have a cumulative effect, increasing the risk of PD for those with more than a single injury.

Protective Factors

Preliminary research indicates certain factors or lifestyle choices may reduce the likelihood of developing Parkinson’s disease. More studies are necessary to determine exactly how effective these are.

Dietary Factors

A diet rich in antioxidants, such as fruits and vegetables, may help protect the brain cells from damage. Foods high in omega-3 fatty acids, like fish, also have a protective effect.

Exercise

Regular physical activity has been shown to have a neuroprotective effect. It can improve motor and non-motor symptoms of PD and may also slow disease progression.

Coffee and Tea Consumption

Moderate caffeine intake in coffee and tea has been associated with a lower risk of developing PD and may be a protective factor. The exact mechanism is unclear, but it may be related to caffeine’s ability to block specific brain receptors involved in PD.

Anti-Inflammatory Drugs

Some studies suggest that regular use of non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen may reduce the risk of PD. However, this is still a subject of ongoing research, and these drugs can have side effects.

Nicotine

Surprisingly, some studies have found that nicotine exposure may be associated with a reduced risk of PD. However, the harmful effects of smoking far outweigh any potential benefit, and researchers are studying alternative sources of nicotine.

Uric Acid Levels

Higher uric acid levels in the blood have been associated with a reduced risk of PD. However, high uric acid can also lead to other health problems, like gout.

It’s important to note that these factors can vary significantly among individuals and do not guarantee disease prevention. More research is needed in many of these areas to understand their impact on Parkinson’s Disease fully.

The Future of Parkinson’s Research

While there’s mounting evidence of the impact of particular environmental factors on PD, plenty of research remains to determine exactly how these relate. Luckily, many passionate scientists are making strides toward gaining an in-depth understanding of Parkinson’s disease!

PCLA proudly features these changemakers at our regular Let’s Talk Parkinson’s virtual events. Check out our recent videos on The Latest in PD Research with Dr. Jeff Bronstein and Environmental Risk Factors for Parkinson’s with Dr. Beate Ritz.