Exercising our immune system during COVID-19
The COVID-19 pandemic continues to have a devastating impact on health, society and the global economy. Worldwide infections are now over 7.5 million with over 420,000 deaths. Unemployment rates have soared and the livelihoods of millions of people are under threat. Government shelter-in-place orders and social distancing guidelines have restricted the movement of ~3 billion people around the globe, separating us from our loved ones and the daily social connections to which we have become accustomed.
This comes with additional challenges to our health and well-being. Feelings of isolation and confinement, coupled with threats to our livelihood, lower our self-esteem and increased feelings of depression, anxiety and distress, which can lead to higher rates of substance use, domestic abuse and suicide.
As an exercise immunologist, I have spent a great deal of time thinking about how exercise can optimize our immune systems to help fend off the threat of this devastating and highly contagious virus. While exercise is widely regarded as a type of medicine in and of itself, our daily activity and exercise routines have been massively impacted by the lockdown and social distancing restrictions that are in effect across the globe.
Gyms and parks, where we would normally participate in our exercise and activity routines, have been closed for some time and have no doubt affected our ability to stay active during this pandemic. As these facilities slowly start to reopen, social distancing guidelines remain in effect and, with the threat of COVID-19 still looming large, many people will remain reluctant to rejoin these facilities and engage in physical activity practices while in close proximity to others.
While it is important to continue practicing social distancing and to take extra precautions with regards to hand-washing and wearing personal protective equipment, it is equally important that we try to stay active during this pandemic.
Regular physical activity exerts a multitude of beneficial health effects but, perhaps more importantly during this pandemic, is its ability to both enhance immune defense and offset the damaging effects that stress can have on our immune systems.
Can exercise protect us from COVID-19?
This has been a topic of great interest since the outbreak of this novel virus, and while no specific studies have thus far been conducted, we do know that higher levels of cardiorespiratory fitness and exercising regularly can improve immune responses to vaccination, lower inflammation and improve immune function in several disease states including cancer, HIV, cardiovascular disease, diabetes, cognitive impairment and obesity.
We also know that physically active people are less likely to report symptoms of upper respiratory illness, and there is evidence that exercise can protect us from many types viral infection, including influenza and rhinovirus. For instance, mice that exercise after being given a lethal dose of influenza live longer and exhibit more favorable immune cell profiles and less inflammation in the lungs.
The reactivation of a latent virus we have previously been infected with but now lies dormant in our body, is a global indicator that our immune system has become weakened. This can occur due to feelings of stress and anxiety brought on by prolonged periods of isolation, confinement and inactivity.
Viruses such as herpes-simplex-virus-1, which causes cold sores, or varicella-zoster virus, which causes shingles, tend to reactivate when we are experiencing increased levels of stress.
A recent study in astronauts, who experience great levels of isolation and confinement stress when in space, found that physical fitness reduced the risk of a latent herpesvirus reactivation during a 6-month mission to the international space station, particularly if they were able to maintain their fitness levels throughout the mission.
Both cardiovascular fitness and muscle strength/endurance were found to be beneficial, and even in those astronauts that did reactivate a virus, the fitter astronauts had lower levels of detectable virus in their saliva indicating they were also less contagious.
Prolonged exposure to stressful situations puts our biological stress response into overdrive, increasing the production of stress hormones such as cortisol that can inhibit many critical functions of our immune system. Specifically, stress causes our immune cells to become less efficient at responding to infectious agents, impairs our ability to mount a protective antibody response, and impairs the trafficking of specific immune cells that patrol through our bodily tissues to hunt for and kill cells that have been infected.
There is a large body of evidence demonstrating that regular exercise of moderate intensity can enhance immune function and it is, therefore, imperative that we strive to maintain recommended physical activity levels during the COVID-19 pandemic.
How does exercise actually improve immunity and reduce our risk of infection?
There are many levels by which exercise can boost our defense system, but a key component is the massive redistribution of immune cells that occurs each and every time we engage in moderate intensity exercise, particularly if the exercise is dynamic and causes sustained elevations in heart rate (e.g., running, cycling or rowing). This is akin to large numbers of soldiers being mobilized so that they may patrol vulnerable areas in our body (e.g. the upper respiratory tract and the lungs) with the mission to hunt and destroy an infectious enemy.
Exercise also has the knack of preferentially mobilizing those highly specialized immune cell sub-types that are particularly effective in migrating towards the tissue and in recognizing and killing damaged or infected cells. This can prevent viruses and other pathogens from gaining a foothold, and may also increase the rate of virus elimination should our immune barriers be breached and we become infected.
When we exercise our muscles release hormone-like proteins called cytokines, which play a key role in regulating many aspects of immunity. These cytokines can direct immune cell trafficking toward areas of infection, increase the production of new immune cells, particularly T-cells, or maintain the existing immune cell compartment to increase our immune defense network.
How much exercise is good?
Physical activity guidelines provided by many governing bodies throughout the world recommend 150–300 minutes of moderate to vigorous intensity cardiorespiratory physical activity per week and two sessions per week of muscle strength training.
While this can be challenging following social distancing and hygienic guidelines with limited access to gyms and parks, there are many creative ways for us to stay active at home.
Home-based exercise platforms, such as online instructor-led classes and ‘exergaming’ (video games which are also a form of exercise), are becoming increasingly popular and are very effective in helping us maintain our activity levels while being confined to our homes.
Specialized technology and equipment is not necessary; keeping active indoors or outdoors through brisk walking, stair climbing, yard/house work and/or playing active games with the family can be just as effective.
What is important is that we avoid prolonged periods (>60-minutes) of time sitting and try to implement even a few minutes of activity at regular intervals throughout the day, all of which count toward achieving these weekly goals.
Exceeding recommended physical activity levels should be avoided as there are strong viewpoints that excessive exercise (e.g. those activities performed by highly athletic individuals) might impair immunity and increase infection risk.
Meeting the recommended guidelines for physical activity might not prevent us from getting COVID-19. However, the direct improvements in immunity coupled with lower levels of stress, would indicate that those of us who are physically active will be less likely to develop severe symptoms, have shorter recovery times, and may be less likely to infect others we come into contact with.
Even when infectious symptoms are mild, low levels of physical activity should still be encouraged to hasten recovery and ameliorate symptoms, provided that adequate social distancing and infection mitigation measures are taken. Exercise is known to improve immune responses to vaccination, especially in older adults who are particularly vulnerable to severe COVID-19 disease.
Boosting immunity through exercise now could pay dividends later when a COVID-19 vaccine becomes available or if a second wave or large spikes in infection rates occur in the near future.
It is important to recognize that exercise is medicine and it can be prescribed in specific doses and formulations in a highly personalized manner. The specific exercise doses and formulations that will be most effective in boosting immunity and lowering risk of viral disease in certain individuals and populations needs to be determined.
Until then, my own personal goal is to make physical activity a daily priority as we continue moving forward through this pandemic. By simply moving our bodies often and limiting the amount of time we spend sitting, our immune systems will be better prepared against the threat of COVID-19.
OTE FROM THE EDITORS: We would like to say a big thank you to Richard for writing this wonderful blog for us. Dr Richard Simpson is an Associate Professor and Exercise Immunologist at the University of Arizona. It is a privilege that he was willing to share his expertise with our readers at InSPIre the Mind and to teach us all about the benefits of exercise for our immunity, especially during this time. Thank you Richard!
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