# Exercise as it relates to Disease/The role of physical activity to reduce the risk of developing Parkinson's Disease

This page is a critique of the paper; Shih I, Liew Z, Krause N, Ritz B. Lifetime occupational and leisure time physical activity and risk of Parkinson's disease. Parkinsonism & Related Disorders. 2016;28:112-117.
The critique was an assignment for the course 'Health, Disease and Exercise' at the University of Canberra.

## What is the background to this research?

Parkinson's Disease is the second most prevalent neuro-degenerative disease in Australia and the United States, with 70,000 Australians currently living with the disease and a projected 1,000,000 people in America by 2030.

### What is Parkinson's?

Parkinson's Disease (PD) is characterized by progressive motor and non-motor impairments, and has the potential to reduce fluidness and co-ordination of gross and fine motor movements throughout the body. The pathogenesis of PD is complex, with a variety of both environmental and genetic factors implicated. PD is characterized physiologically by a progressive dopamine depletion and a loss of neurons in an area of the brain called the substantia nigra.
Prior to full development of PD, there are a number of non-motor symptoms exhibited such as pain, depression, anxiety, cognitive dysfunction and sleep problems. As the disease progresses, motor symptoms begin to develop such as resting tremors, freezing of gait, rigidity and slow movements.
There has been a large amount of research focusing on the use of exercise to treat the symptoms of PD, however there is now some emerging evidence to suggest that there may be pre-morbid benefits of exercise.
The purpose of this paper was to build on this research and investigate whether occupational and leisure time activities reduce the risk of developing PD.

## Where is the research from?

The research was conducted from these institutions:
* Department of Epidemiology, Fielding School of Public Health, University of California at Los Angeles, California, USA
* Department of Environmental Health Sciences, Fielding School of Public Health, University of California at Los Angeles, California, USA
* Department of Medicine, University of California at Los Angeles, California, USA
There was some funding received from the American Parkinson's Disease Association, however there was no reported conflict of interest.

## What kind of research was this?

This study was a retrospective, population-based case control study. Case control studies investigate the effects of a given intervention within a given population and compare them to a control group.
| Advantages | Disadvantages |
| Able to involve large cohort and establish associations | Prone to selection bias by researchers |
| Cheaper to conduct than prospective study or randomised trial | Retrospective data, therefore prone to recall bias |
| Good for studying effects of intervention and disease | Unable to give as reliable information regarding effects of intervention compared to RCT with comparable groups at baseline |

## What did the research involve?

Parkinson's patients were identified based on recent diagnosis and geographical location. Potential subjects were contacted by email, letter or telephone and were screened for eligibility.
Eligibility criteria:
* Being > 35 years old.
* Not too ill to participate
* Currently living in one of three designated counties
* Lived in California for > 5 years.
Population controls were selected by medicare lists and had to be > 65 years and live in one of three designated counties.
Blinded interviewers then collected data by conducting structured telephone interviews to obtain demographic and physical activity information including;
* Overall PA level across 4 age periods; 18-24 years, 25-44 years, 45-64 years & > 65 years
* History of participating in competitive sports
* Occupational histories

## What were the basic results?

The study determined that after comparing the PD group (n = 357) to the control group (n = 341) that there were an association between lifetime exercise and a lower risk of PD. The main findings from the study were:
* Higher levels of self reported lifetime PA were associated with decreased PD risk.
* 44% lower risk of PD among those with moderate to vigorous PA of at least 189 MET hours per week on average in adulthood, similar results found over all 4 age groups.
* Participants who remained highly active throughout lifetime were at the lowest risk of PD.
* Competitive sports are associated with decreased PD risk.
* Occupational PA not associated with PD risk.

### How did the researchers interpret the results?

The researchers interpreted that physical activity appears to be protective against developing PD. However, they did note that the extended period between onset of initial symptoms and progression makes it difficult to conclude whether PD leads to a reduction in PA years before becoming symptomatic.

## What conclusions can we take from this research?

This article has shown that there is still more research that needs to be conducted into the benefits of lifetime physical activity and how it reduces the risk of developing PD. The results from this study align with similar research in the area which have found that there are benefits of exercise in PD patients in terms of cognitive functioning, motor functioning and enzyme expression, when looking at pre-morbid exercise status. There has been some research into the neuro-protective effects of exercise in mice, which also reveals promising results.
This area of research will be an interesting topic in the future, particularly with the abundance of the literature regarding the benefits of exercise for treating symptoms of PD. There will need to be more high-quality studies to ensure that the best evidence-based practice is implemented and the correct dosage and type of exercise is found. There is also the possibility that the proposed benefits of physical activity may in fact be markers for genetic and biological factors that lowers the risk of developing PD.

## Practical Advice

This research has shown that physical activity and participation in sports during youth and remaining physically active throughout life appears to be beneficial in reducing the risk of developing Parkinson’s Disease.
However, there needs to be more research conducted to understand how these proposed benefits impact us physiologically and how much exercise would be optimal to reduce the risk of developing PD.

## Further information/resources

For further information on Parkinson's and how physical activity is beneficial;
http://www.parkinson.org/understanding-parkinsons/treatment/Exercise
https://shakeitup.org.au/understanding-parkinsons/
http://brainfoundation.org.au/disorders/parkinsons-disease

## References

* 1 2 3 4 5 6 7 8 9 10 Shih I, Liew Z, Krause N, Ritz B. Lifetime occupational and leisure time physical activity and risk of Parkinson's disease. Parkinsonism & Related Disorders. 2016;28:112-117
* 1 2 3 4 5 Flach A, Jaegers L, Krieger M, Bixler E, Kelly P, Weiss E et al. Endurance Exercise Improves Function in Individuals with Parkinson’s Disease: A Meta-analysis. Neuroscience Letters. 2017;.
* ↑ What is Parkinson's [Internet]. Parkinsons.org.au. 2015 [cited 6 September 2017]. Available from: http://www.parkinsons.org.au/what-is-parkinsons
* 1 2 3 Bellou V, Belbasis L, Tzoulaki I, Evangelou E, Ioannidis J. Environmental risk factors and Parkinson's disease: An umbrella review of meta-analyses. Parkinsonism & Related Disorders. 2016;23:1-9.
* 1 2 3 Sunwoo M, Lee J, Hong J, Ye B, Lee H, Oh J et al. Premorbid exercise engagement and motor reserve in Parkinson's disease. Parkinsonism & Related Disorders. 2017;34:49-53.
* 1 2 Jang Y, Koo J, Kwon I, Kang E, Um H, Soya H et al. Neuroprotective effects of endurance exercise against neuroinflammation in MPTP-induced Parkinson's disease mice. Brain Research. 2017;1655:186-193.
* 1 2 3 Koo J, Jang Y, Hwang D, Um H, Lee N, Jung J et al. Treadmill exercise produces neuroprotective effects in a murine model of Parkinson’s disease by regulating the TLR2/MyD88/NF-κB signaling pathway. Neuroscience. 2017;356:102-113.
* 1 2 Sääksjärvi K, Knekt P, Männistö S, Lyytinen J, Jääskeläinen T, Kanerva N et al. Reduced risk of Parkinson’s disease associated with lower body mass index and heavy leisure-time physical activity. European Journal of Epidemiology. 2014;29(4):285-292.