Identification of avoidable risk factors for Parkinson’s Disease

A recent Npj Parkinson's Disease study identified avoidable risk factors for Parkinson’s Disease (PD).

Study: Population fraction of Parkinson’s disease attributable to preventable risk factors. Image Credit: meeboonstudio/Shutterstock.com

Background

Based on the current scenario, the most effective way to reduce the global incidence of PD is by eliminating risk factors.

Although many studies have estimated the relative risk or odds ratio (OR) linked to PD manifestation, these studies have not assessed the impact of different PD factors on disease burden.

For instance, exposure to chemicals used by the military imposes a greater risk of PD, compared to being exposed to common pesticides or herbicides. However, both types of chemicals have different disease burdens because one chemical is rarely used, while the other is handled frequently.

About the study

The current study estimated the population attributable fraction (PAF), which is defined as the percentage of the disease that could be prevented by controlling the risk factors.

PAF helps understand how each risk factor influences the disease burden this information is effectively used to formulate interventions to control the disease. To date, no document on the PAF associated with PD has been available.

A total of 981 persons with PD (PwP) and 485 neurologically healthy controls (NHC) were recruited.

Community volunteers and patients’ spouses were assigned to the NHC group. Specialist neurologists diagnosed individuals in the PwP group to confirm PD diagnosis.

Participants from the Deep South of the United States were recruited in two waves, i.e., between July 2015 and July 2017 and between October 2018 and March 2020.

Since the risk factors associated with PD incidence in the Deep South of the United States have been understudied, they were considered in this study. 

Individuals selected in this study completed two questionnaires: the Gut Microbiome Questionnaire (GMQ) and the Environmental and Family History Questionnaire (EFQ).

It must be noted that 74% of PwP and 77% of NHC returned the fully completed questionnaires. Hence, a total of 808 PD and 415 NHC cases were analyzed in this study.

Study findings

The PwP group included 63% males. Compared to the control group, the prevalence of weight loss, constipation, and rapid eye movement sleep behavior disorder (RBD) were high in the PwP group.

Two of the risk factors of PD found in the Deep South were family history of PD and exposure to pesticides/herbicides. These factors enhanced PD risk in both genders. One feature commonly detected in PD patients is mild/moderate traumatic brain injury (MTBI) that requires hospitalization or causes concussion. However, these occurrences could be due to reverse causality.

Importantly, MTBI/concussion was found to be insignificantly linked to PD when censored to 10 years prior to the onset of PD. This study assessed whether repeated blows to the head while playing a sport or during combat are risk factors for PD.

Interestingly, these factors were positively correlated with PD incidence in men. No females reported blows to the head, therefore, a similar link could not be established. Similarly, exposure to military-grade chemicals posed a higher risk among males.

The next step was to calculate the PAF for the modifiable risk factors. In doing so, the OR adjusted on all risk factors was used.

The adjusted PAF for pesticide/herbicide exposure was lower among men (17%) than women (23%). Additionally, the PAF among men was 6% for military chemical exposures and 10% for blows to the head. Overall, military-related chemicals, pesticide/herbicide exposure, and blows to the head were responsible for 30% of PD in men.

This study's findings align with previous studies that indicated a higher incidence of neurological disorders in football players. It was observed that these athletes report high rates of depression, cognitive loss, dementia, and chronic traumatic encephalopathy.

Interestingly, these observations have failed to dim the popularity of collision sports among boys. Furthermore, an increase in the participation of school-age girls has been observed. 

Conclusions

The current study has some limitations, including an inability to identify a single chemical linked to PD. All calculations are based on self-reported exposures to pesticides/herbicides; however, exposures to the same chemicals through other sources (e.g., contaminated fruits, vegetables, water, fish, and meat) were not considered.

PAF estimates cannot be generalized because they vary across populations depending on the type and prevalence of risk factors.

Despite the limitations, this study documented evidence that revealed that repeated blows to the head, which normally do not require medical care, increase the risk of PD by twofold.

This kind of injury commonly occurs in collision sports like football. Importantly, several modifiable risk factors of PD in both males and females were identified in this study.

The findings imply that PD incidence can be prevented in some populations by eliminating these risk factors.

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.