Lay summary by Erin Tonkiss, reviewed by Dr Scott Allen and a MND/PD/Dementia lay panel
Background
This study aimed to assess how physical activity (exercising three or more times per week) can affect neurodegenerative diseases, with a focus on aging populations. The diseases discussed are; motor neurone disease (MND), Parkinson’s disease (PD), and Alzheimer’s disease (AD).
Motor neurone disease is a condition where the nervous system is progressively damaged leading to muscle weakness. Early stages of MND include slurred speech, hoarseness, difficulty swallowing, emotional liability, loss of tongue contour, excess saliva, difficulty breathing, muscle wasting and twitching.
Parkinson’s disease is a condition where parts of the brain become progressively damaged, slowing movement. PD typically begins with tremors, muscle stiffness, difficulty standing or walking, changes in speech, slow movement, impaired posture and balance and loss of automatic movements.
Alzheimer’s disease is a progressive brain disorder causing problems with memory, thinking and behaviour. Early symptoms of AD include memory loss, misplacing items, forgetting names of places and objects, becoming less flexible and more hesitant to try new things, repeating the same question.
There are currently no curative therapies for MND, PD and AD. However, this paper discusses how altering the amount of physical activity someone with MND, PD or AD carries out could contribute to slowing the disease progression and improving the disease outcome. Targeting these factors could be effective in reducing symptoms.
Physical activity has recently been of interest to neurologists as there is increasing evidence that it has a role in maintaining brain health. Physical activity does not only play a large role in motor function and physical health, but also has an effect on mental wellbeing. However, it should be noted that this paper focuses mainly on the physical side rather than the mental side of neurodegenerative diseases. So, even though physical activity may improve mental wellbeing, this paper aims to identify the risks of developing neurodegenerative diseases when physical activity is increased.
Why is this study important?
This study shows the importance of how physical activity could affect the risk of developing neurodegenerative diseases. So, if there is a risk, then reducing the amount of physical activity one carries out could be beneficial in slowing the progression of neurodegenerative diseases.
How was physical activity investigated?
This study used a method called Mendelian randomization. Mendelian randomization is a way for researchers to see links between two factors, one being an exposure (in this study the exposure was physical activity) and the other being an outcome (in this study the outcome was neurodegenerative diseases (MND, PD and AD). Furthermore, Mendelian randomization can provide information as to whether a factor is a cause or result of a disease, and so can identify factors causing a disease. Mendelian randomization was carried out by using information from the public genome-wide association study (GWAS). This is where genetic information from a large population is studied to observe specific traits. These traits were physical activity engagement and neurodegenerative diseases (MND, PD, AD). This genetic information was used for Mendelian randomization. Multiple different Mendelian randomization methods were carried out to get a good estimation of the effects of physical activity on neurodegenerative diseases. These methods aimed to assess the direct link between physical activity and neurodegenerative diseases, so no other known factors should have affected the results.
What were the results?
Physical Activity with Parkinson’s Disease (PD)
Mendelian randomization did not show any consistent data providing evidence of an effect of physical activity on the risk of developing Parkinson’s diseases. However a trend towards reduced risk of PD was observed with increased physical activity levels. However, more research is needed to make firm conclusions and for physical activity to be recommended to people with PD.
Physical Activity with Alzheimer’s Disease (AD)
The methods of this investigation showed that there was no noteworthy data suggesting an association between physical activity and AD.
Physical Activity with Motor Neurone Disease (MND)
There was enough significant data from the Mendelian randomization methods to show that physical activity may actually increase the risk of MND.
What do the finding mean going forward for people with neurodegenerative diseases?
The results from this research showed that there were no significant findings to show a link between physical activity and Parkinson’s disease (PD) or Alzheimer’s disease (AD). So, it can be concluded that an increase in physical activity engagement does not increase the risk of PD or AD. But may decrease the risk of PD.
For motor neurone disease (MND) this study showed that physical activity did have a significant effect on the risk of developing MND. Increases in physical activity participation could subsequently increase the risk of MND. Further research should be done as to whether advising less exercise to people predisposed to developing MND could be beneficial in reducing the risk of developing the disease.
Final Thoughts
The positive effects of physical activity on mental wellbeing could be taken into account in further research. Does mental wellbeing have an effect on the risks of developing neurodegenerative diseases? If so, should people diagnosed with motor neurone diseases (MND) or who are predisposed to MND limit the amounts of physical activity they undergo if it has an important role in their mental wellbeing? Further research must be done before any definitive conclusions can be made.
This paper is in agreement with a paper by Thomas H Julian (Julian et al., 2021) from the University of Sheffield. In this study they discuss similar methods of Mendelian randomization providing evidence for physical exercise being a risk factor for motor neurone disease (MND). The conclusions from both papers were similar in that there was a relationship between physical activity and MND.
This study can be found at Frontiers | Physical activities and risk of neurodegenerative diseases: A two-sample Mendelian randomization study (frontiersin.org)
Paper title: Physical activities and risk of neurodegenerative diseases: A two-sample Mendelian randomization study
Author list; Qiao Liao, Jian He and Kun Huang.
Publication details including date of publication.
Published by Frontiers in Aging Neuroscience.
Published 23rd September 2022.
Reference; Julian, T. H., Glascow, N., Barry, A. D. F., Moll, T., Harvey, C., Klimentidis, Y. C., Newell, M., Zhang, S., Snyder, M. P., Cooper-Knock, J., & Shaw, P. J. (2021). Physical exercise is a risk factor for amyotrophic lateral sclerosis: Convergent evidence from Mendelian randomisation, transcriptomics and risk genotypes. EBioMedicine, 68, 103397. https://doi.org/10.1016/j.ebiom.2021.103397