Exercise is one of the best things a person can do to help protect themselves from chronic degenerative disease. Over 180 favourable biochemical changes occur in the body after exercise including reducing chronic inflammation, up-regulating antioxidant enzymes and enhancing immune surveillance [Thomas].
This post explores if these properties could help protect us against Covid-19, mitigate the consequences of an infection and if so, what’s the best way to exercise and how can its benefits be enhanced with diet.
Exercise, immunity and viral infections
The relationship between exercise and the immune system is complex and not always obvious. What’s has been firmly established is that regular graduated exercise slows the natural decline of our immune system as we grow older or suffer from deficiencies associated with diabetes, poor gut health and obesity. Sensible exercise regimens reduce excess inflammation while increasing levels of catecholamines which stimulate the recruitment of neutrophils, lymphocytes and monocytes – including NK, CD4+ T cells and B cells – into the peripheral blood [Hoffman-Goetz]. This improvement in immune surveillance apparatus has been linked to a reduced risk of infection, as demonstrated by a study which highlighted how individuals who regularly performed >2 hrs of moderate exercise per day reported a 29% reduction in risk of upper respiratory tract infections compared to those leading a sedentary lifestyle [Matthews].
On the other hand, if exercise is too strenuous, it is followed by decreased concentrations of lymphocytes and impaired cellular-mediated immunity [Hoffman-Goetz]. One study outlined how there was an increased risk of infection in the weeks following ultra-endurance running events [Pendersen], while another investigation revealed that people conducting rigorous or unaccustomed exercise had a higher incidence and severity of upper respiratory illness [Fitzgerald, Friman, Weidner].
Exercise and oxidative stress
A serious complication of SARS-CoV infection is the sudden development of excessive inflammatory pulmonary infiltrates which cause severe respiratory distress – a development which is referred to as a cytokine storm. Studies have shown that damaging reactive oxidative species (ROS) produced by macrophages infiltrate are implicated in the development of these complications [Uchide]. Factors which improve anti-oxidant enzyme efficiency such as exercise, diet and improved gut health are certainly worth further consideration.
As with immunity, the relationship between exercise and oxidative stress is complex. At the start of an exercise session, reactive oxidative species (ROS) are generated as a by-product of normal energy-producing mechanisms (oxidative phosphorylation). In response to this transient increase in ROS, the adaptive up-regulation of antioxidant genes results in greater production of antioxidant enzymes via activation of Nrf-2 [Fehrenbach, Kodja]. In the long term, however, provided individuals continue a sensible, graduated exercise regimen, exercise can be regarded as an anti-oxidant [Poljsak, Ristow, Schulz, Son]. Studies have confirmed that individuals who consistently exercise have better levels of antioxidant enzymes in their muscles and synovial fluid, although it should be noted that even elite athletes are prone to episodes of excess oxidative stress when their level of exercise intensity increases [Fehrenbach, Kodja]. This initial increase in oxidative stress can be a serious issue for individuals who begin an exercise programme too vigorously, especially among those who are unaccustomed to exercise or over 50 years of age, for whom biological adaptive processes are slower [Poljsak, Ji]
Exercise and mood
Low mood, fatigue, anxiety and depression triggered by social isolation, financial trouble during lockdown are factors which cannot be underestimated. Fortunately, regular exercise, especially if in groups, combined with relaxation, mindfulness and healthy eating programmes can elevate mood, self-esteem, reduce anxiety and depression [Young]. The biochemical mechanisms by which exercise elevates mood are multifactorial but include increased brain oxygenation, better endorphin, serotonin and monoamine release, and rises in core temperatures [Salmon].
In addition, if exercising outside, sun exposure can increase vitamin D, lower levels of which are linked to greater risks of both depression and arthritis. Increased light exposure, has been linked to a reduction in non-seasonal depressive disorders improvements in circadian rhythm [Lam].
Dietary considerations when exercising
When exercising regularly, close attention to diet is needed in order to avoid mineral and vitamin deficiencies, while ensuring adequate hydration, protein, carbohydrate and polyphenol levels. Exercising while on a poor diet can be futile and even counterproductive.
Minerals and vitamins:
The best way to ensure good mineral intake (particularly zinc, copper and selenium) is via a varied diet rich in seafood including oysters, clams, fish, seeds, nuts and leafy green vegetables. If individuals do not regularly eat these foods, a mineral supplement may be worthwhile.
When starting to exercise vigorously, ensuring a higher than average intake of the entire spectrum of vitamins is important. Vitamin C is particularly helpful as it helps facilitate DNA repair and can also improve immune efficiency but if considering a supplement ensure it includes citrus bioflavonoids as these have reported anti-viral properties. When it comes to other vitamin supplements, however, there are concerns with the direct antioxidants Vitamin A & E, as there is data to suggest that these can upset the normal oxidative balance. This is because the production of anti-oxidant enzymes is stimulated by the presence of some free radicals, so an individual taking high dose vitamin E or A could remove the stimulus for the adaptive formation of natural anti-oxidant enzymes. There is also a risk of creating too much of an anti-oxidant effect when physical activity has finished, increasing genetic damage, impeding joint and tissue repair and mitigating the other health benefits of exercise [Teixeira, Poljsak, Ristow, Peternelj, Avery].
As well as reducing inflammation, polyphenols can help reduce excess oxidative stress within tissues. Their antioxidant-enhancing properties stem from an ability to facilitate activation of the transcription factor NF‐E2–related factor 2 (Nrf2), which enhances an appropriate antioxidant response to damaging reactive oxidative species [Stivala, Davidson, Juge, Dinkova‐Kostova]. Polyphenols also promote the natural adaptive response to ROS during exercise yet do not affect the degradation of antioxidant enzymes after exercise, greatly extending the time cells spend with optimal oxidative balance [McMahon, Poljsak, Ristow, Teixeira].
Polyphenols also protect joints, improve muscle recovery and aid aerobic recovery, which explains why they are being investigated as a means to improve exercise uptake in those with arthritis, and why many athletes are increasingly finding ways to boost their intake with diet and supplements in order to enhance performance [Myburgh].
Laboratory studies have also reported that certain polyphenol-rich foods can have potential direct antiviral effects by reducing viral attachment, penetration, absorption and proliferation [Maher, Jassim, Sun, Li, Lin, Kumar, Mycol, Yagi, Syed, kotwal, Park]. Clinical benefits have not been established, but studies involving boosting polyphenol intake among people with Covid-19 are underway [The UK Phyto-V study].
Probiotics and pre-biotics
Some polyphenols, such as plant lignans found in nuts, resveratrol in red wine and ellagitannin found in tea, celery, pomegranate, and turmeric, act as prebiotics for healthy bacteria, improving gut health and integrity and, consequently [Powanda]. Laboratory and clinical studies have shown that increased toxin exposure due to poor gut health can lead to immune and inflammatory dysfunction [Shen]. Studies looking at the elderly have shown that enhancing the diet with a probiotic supplement could help reduce age-related falls in natural killer cell activity [Gill]. A study from Australia involving healthy athletes compared a probiotic polyphenol pill with a placebo. After one year, the intervention group had fewer colds and less disruption to their training. Several other studies have shown that regular intake of live lactobacilli shortened the duration and severity of upper respiratory tract infections [Fujita, Rerksuppaphol]. In 2011, a summary of all international studies was published in the prestigious Cochrane Database of Systematic Reviews and concluded that probiotics also reduced the incidence of upper respiratory tract infections [Hoa]. Interventions exploring lactobacillus probiotics (with prebiotics) and Covid-19 are ongoing ...read more.
Exercise after catching Covid-19
Once an individual catches an upper respiratory viral illness, it is important to stay mobile, even though fatigue and muscle aches can make this difficult. Obviously, this mobility would have to remain within the confines of your house, flat or garden (even after lockdown). Blood clots are emerging as a serious complication of Covid-19, and it should be noted that embolisation to the lung is a major contributor to life-threatening respiratory distress. Avoiding immobility is one of the best ways to avoid blood clots, while steering clear of strenuous exercise is also recommended as the virus can affect pulmonary, cardiac, and skeletal muscle functions and there is a risk of heart or muscle damage (cardiopathy and myopathy) [Basso, Trachtenberg, Woodruff]. In general, people with Covid should increase mobility if they previously did very little, but ease off if they were previously very active. After an individual has passed the worst of a Covid infection, exercise will help recovery and clear mucous and debris from the airways.
Regular graduated exercise is an excellent way to prevent deterioration of the body’s immune system as we get older or to help mitigate the higher oxidative stress and chronic inflammation associated with other conditions such as diabetes, obesity and poor gut health, all of which are of concern during the current Covid-19 pandemic. Excess or unaccustomed exercise, however, especially in tandem with a poor diet, can be counter-productive. Exercise needs to be planned sensibly, and extra attention should be given to mineral and polyphenol-rich foods when embarking on a new regimen. If infected with Covid, individuals should try and stay mobile while avoiding overly strenuous exercise levels until symptoms resolve.
In the longer term, it’s important to find an exercise programme which you enjoy and reflects your abilities, available time and goals. Even after lockdown, it may be better to avoid exercising in stuffy gyms and instead opt for a local park or beach. Each session should emphasise whole-body conditioning and ideally last about an hour at an intensity which gets you a little breathless, hot and sweaty. Ideally, sessions should include a warm-up, some aerobic and resistance training, some balance tasks, and then a cool down and specific stretches. On top of these regular sessions, introducing Pilates will improve strength, posture, mindfulness and flexibility.
Prof Robert Thomas
Bedford and Addenbrookes. Cambridge University Trusts
Professor of exercise and nutritional Science
University of Bedforshire
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