Physical activity and MND – part 1
Every month the Research Information team looks at ‘the stats’ for the MND Research blog. These show us how many times each of our blogs are looked at and, every month, ‘Physical activity and MND – is there a link?’ features in the top five. This is possibly driven by media stories of professional sportspeople who have been diagnosed with MND. As we receive a lot of emails about this subject, we felt it was about time for an update as ‘the stats’ suggest this is a topic close to people’s hearts.
This is the first of three blog articles looking at MND and physical activity and other factors that may, or may not, play a role in the development of the disease.
As this blog was being written, a paper, by Visser and colleagues, was published in the Journal of Neurology, Neuroscience and Psychiatry, which investigated the association between physical activity and MND in a large multi-centre study. You can read our blog article about the paper here.
In summary, the authors believe they have shown a significant positive relationship between physical activity and likelihood of developing MND. The study concludes there is a 6% increase in risk of developing MND to people with high activity levels.
To put this into some perspective, this is a 6% increase in risk of something that conveys only a very low risk to begin with. The authors themselves state that this is not a major factor in the development of MND and the benefits of exercise with regard to other life-threatening conditions, such as cardiovascular disease, far outweigh the risk of developing MND by physical activity.
Back to the blog
The enquiries we receive about physical exercise tend to fall into two categories:
1) Did the amount of physical activity I undertook before my diagnosis cause my MND?
2) Can I continue with physical activity after my diagnosis, or will this make my MND worse?
Physical activity ranges from gentle exercise (like walking) to more vigorous daily activity (like working out at a gym), to the levels achieved by professional sportspeople and elite athletes.
This article is going to try to answer the first question.
A brief overview of available evidence
In 2013 we reported on the results from a study, carried out by a team from the University of Sheffield, which identified that higher levels of physical activity appeared to be a definite risk factor for the non-inherited form of MND (known as ‘sporadic’ MND). As most people who are physically active do not develop the disease, it was suggested that the observed increased risk is probably due to a subtle combination of several environmental/lifestyle factors, of which physical activity is one, rather than physical activity alone.
In 2014, one study found that overall physical activity was associated with a reduced likelihood of developing MND, and even suggested that physical activity may be protective against the disease. They cited several other, older, studies that supported the notion that physical activity is not a risk factor for MND.
A 2016 study concluded that increased physical activity was associated with a reduced risk of dying from MND for most people. However, they also suggested an increased risk of MND in certain sub-groups: individuals who are obese, or who have a high BMI due to substantial increase in muscle mass may be at greater risk from vigorous physical activity. The researchers suggest that further investigations may confirm this is due to ingestion of performance enhancing drugs to increase muscle mass or compounds that promote weight loss.
Another study in 2016 studied exposure to environmental factors in 92 people with MND. They looked for an association between physical activity and drug intake, head trauma and participation in specific sports (football, ice hockey) and age at symptom onset. No relationship between vigorous physical activity and age at symptom onset was seen. In former football and ice hockey players, the rate of vigorous activity was higher but frequency of head injuries and analgesic (pain killer) intake were not different compared to other people living with MND. History of head injuries was the only environmental risk factor associated with accelerated neurodegeneration in MND as well as other neurodegenerative diseases such as Alzheimer’s and Parkinson’s disease.
These studies support the suggestion made by the Sheffield researchers in 2013 that it is not increased physical activity per se, but other unknown environmental factors that increase MND susceptibility. However, in the light of the research recently published by Visser this is now called into question. Although it remains unlikely that vigorous physical activity by itself causes MND, and it is more probable that a combination of environmental factors associated with physical activity contribute to the development of the disease, no obvious causative factors emerged from the Visser study.
However in a 2016 study, again carried out by researchers at Sheffield, which asked 175 individuals newly diagnosed with sporadic MND and 317 matched controls, about energy expenditure and time spent in vigorous-intensity physical activity, found that participation in exercise, equivalent to approximately 45 minutes brisk walking a day, was consistently associated with an increased risk of developing MND.
So what does this mean?
The stories about MND and physical activity that make it into the media feature prominent sports people who have been very active for a number of years. While this is good for raising awareness of the disease, it also raises concerns for people living with MND.
To add more fuel to the fire, in 2010 McKee and colleagues suggested that a newly defined neurodegenerative disease – chronic traumatic encephalopathy – often resulting from repeated head injuries could be the underlying reason for MND cases observed among professional athletes and perhaps also among military veterans.
These studies continue to pose the question: ‘Does physical activity cause MND?’ The honest answer to that is ‘we still don’t know for sure’. If you were very active before diagnosis the conveyed risk is still very, very small. And let’s not forget that there is still plenty of evidence to support the suggestion that it isn’t the amount of physical activity per se but some other, as yet unknown, environmental factor that increases the risk of developing MND.
According to the World Health Organisation (WHO), insufficient physical activity is one of the leading risk factors for global mortality and is on the rise in many countries. People who are insufficiently active have a 20-30% increased risk of death compared to people who are sufficiently active. The WHO recommendations for activity levels can be found here. Therefore, a sedentary lifestyle is not recommended as the benefits of any exercise undertaken before diagnosis far outweigh the possible risks that physical activity contributed to the development of the disease. Continuing exercise, albeit in a limited format, is also important once a diagnosis of MND has been made and this will be discussed in part two of this trio of physical activity related blogs.