Exercise in the era of covid-19: what should we do?

It is many months since I last posted.  I had been unable to run for many months in 2019 on account of debilitating illness.  As a result, my attention was taken up by other things and blogging was not a priority.  Fortunately, I was able to recommence running again at the end of December, and have been running regularly since then.  I am recovering fitness slowly.

I ended my post in June 2019 with the statement that my next post would examine the issue of what a distance runner might do to enhance their longevity as a runner.  I still intend to address that question in the future.  My recent experience of the slow process of regaining my former fitness has increased my determination to understand more about the optimum ways to maintain longevity as a runner.  But meanwhile, a more urgent issue has emerged.  Corona virus is sweeping though most countries on earth.  The risk of serious illness or death, especially for the elderly, and the threat that health services will be overwhelmed, is now a pressing issue facing us all.  Running no longer appears so important.

At least in the UK, where the Corona death toll has just passed 100, the situation is not yet anywhere near as devastating as it has been in Wuhan or in Italy.  It is a time when governments and individuals are trying to identify the best course of action, yet there are so many things that are unknown.  If the pandemic persists for many months, we need to take seriously what we can do to maintain our health in the longer term, when many aspects of our lives are likely to be seriously disrupted.

At least for the present time, the UK government recognises the importance of exercise for the elderly. Exercise is also important for the young. Whatever our age, we share a responsibility to do what we can to minimise the probability that we will become clinical cases, infecting others and perhaps even needing admission to an over-stretched hospital.  Good hygiene and social distancing are the essential requirements.  Nonetheless, exercise too has a role to play in minimising the risk that we will become ill.

There are many individual scientific studies that support this claim, though it is best not to place too much emphasis on a single study. In this review I will place emphasis on the consensus conclusions drawn by reputable experts from extensive review of the evidence. But bear in mind that even experts are sometimes influenced by the zeitgeist. I should also mention at this point that I am a medically qualified biomedical scientist, who, over a period of many decades, has practised as a medical doctor and also carried out research in diverse fields including biochemistry and physiology. I retired from clinical practice almost nine years ago. I am currently a neuroscientist working mainly in the field of mental health I will draw mainly on evidence regarding respiratory infections in general, though where possible I will make specific reference to covid-19, the illness produced by the corona virus.

The effects of exercise on resistance to infection depends on many factors including the fitness of the individual, the nature of the exercise and the timing in relation to exposure to the virus. An extensive review of many experimental studies of exercise in animals indicates that exercise or training before infection has either no effect or decreases morbidity and mortality from respiratory infections. Exercise during the incubation period of the infection appears to have either no effect or increases the severity of infection. ncbi.nlm.nih.gov

In humans it is less feasible to perform a well-controlled comparison of the period before infection with the period during incubation. However, the available evidence is consistent with the bi-phasic relationship observed in animals. A well regarded expert consensus statement (the BASES statement) concluded: Regular moderate exercise reduces the risk of infection compared with a sedentary lifestyle, but very prolonged bouts of exercise and periods of intensified training are associated with an increased risk of infection. doi.org

The simple message

A more recent consensus statement by a group of experts convened by the International Olympic Committee is consistent with the BASES consensus statement. They produced a simple pictorial summary of the evidence relating to risk of illness related to athletic training.  https://www.ncbi.nlm.nih.gov/pubmed/27535991.

Illustration of the J-shaped relationship between training load and risk of illness (from Schwellnus et al, Br J Sports Med. 2016 Sep;50(17):1043-52

 

This is a simplified illustration. The risk for an individual depends on many factors including their natural resilience against illness, and many other variables including their current level of fitness; how well rested they are; general nutrition, how well fuelled they are during exercise, and many other life-style related factors. There is some evidence that elite athletes tend to have exceptional resilience and hence have an increased capacity for a high training load without increased risk of illness, illustrated by the dotted line.

In this blog I will do my best to assemble the science-based information about the many factors that influence the effect of exercise on the response to infection.

The incubation period

Covid-19 is now circulating in our community, and any of us might possibly be in the incubation period.

However, provided you feel well, the chance that you are incubating covid-19 is low, at least in the UK at present. Continuing moderate training is likely to strengthen your immune system. With many races cancelled in the near future, it is probable that few of us want to continue intense training in the near future. However, if you do, you should be cautious about the amount of heavy training. We will address this further below.

If you have respiratory symptoms you need to take careful stock of the situation. The usual rule of thumb among runners is that if you have respiratory symptoms above the neck, training is OK. The problem with covid-19 is the early symptoms are often above the neck; most notably cough. A recent onset cough is one of the key signs that you should be self-isolating. You should not be training. Light activity to maintain mobility is probably OK, but also ensure you get adequate rest.

If you have a sore throat without cough, a cold is more likely but covid-19 is possible. I would suggest that you take your temperature before training. Elevated temperature is the other key sign indicating that you should self-isolate. If you have an elevated temperature, ensuring adequate rest is a high priority

Nutritional status

The cells of the immune system are heavily dependent on adequate glucose to meet their energy requirements. Many studies suggest that the most effective nutritional strategies for athletes, include a substantial intake of carbohydrates sciencedirect.com Carbohydrate intake during prolonged and intense exercise is associated not only with higher glucose level in the blood but also lower stress hormones and lower levels of chemical messengers that promote inflammation.

Carbohydrate intake makes an important contribution to optimising immune defence during exercise. Various micronutrients (vitamins and minerals) also play a role. Therefore, if you are engaging in regular exercise while at risk of exposure to covid-19, it makes sense to consume an adequate amount of carbohydrates, within a diet that includes vegetables and other sources of vitamins and minerals.

Sleep

Humans evolved to live on a planet that revolves on its axis generating a 24 hour cycle of day and night. Hormonal activity and immune function fluctuate with a 24 hour circadian rhythm that optimizes our readiness to forage or hunt in the daytime and recuperate during the night time. A surge of growth hormone that promotes body repair is released within the first 2 hours of going to sleep. In contrast, release of the stress hormone, cortisol, rises towards dawn and reaches a peak around waking time to mobilise glucose and provide fuel for a diverse range of bodily activities. Cortisol subsequently falls to a low level by evening.

Many of the messenger molecules that control the immune system fluctuate in synchrony with the daily fluctuation of cortisol. The relationship between cortisol and immune function is complex. While cortisol mobilises glucose and promotes energy metabolism, thereby supporting the function of the cells of the immune system, sustained elevation of cortisol suppresses the immune system. Good health depends on a well-regulated, coordinated daily variation of cortisol and the immune system. Chronic sleep deprivation, and also chronic excessive sleep are associated with diminished life-expectancy. For the typical person, between 7 and 9 hours sleep per day is optimal. Sleeping pattern potentially plays an important role in ensuring that moderate exercise enhances rather than harms immune function. I do not know of any specific data on sleep and resistance to covid-19, but it is almost certain that a healthy sleep pattern will help optimise defence.

I was a junior hospital doctor in the years long before the European Union Working Time Directive came into force. In those days we worked very unhealthy long hours. There might be pressure on hospitals to relax working time restrictions for front-line staff in the coming months. For the good of all of us, I hope those pressures can be minimised. Meanwhile, those of us who are at home chaffing at the bit because our social activities are restricted should use this opportunity to improve our sleeping habits.

Hydration

Dehydration increases the risk that exposure to the virus will result in infection. The upper airways are lined with hair-like cilia that sweep invading material, including viruses, wrapped in mucus, upwards and out of the system. If the airways become too dry the cilia get clogged and cannot sweep the viruses out, making it easier for the virus to invade the cells lining of the airways. The virus causing covid-19 prefers dry surfaces.

Life-style factors

Alcohol interferes with immune function in several different ways. ncbi.nlm.nih.gov Alcohol disrupts the function of the cilia in the upper airways, and impairs the function of immune cells. Excessive alcohol consumption increases susceptibility to pneumonia and in particular increases the likelihood of acute respiratory distress syndrome – one of the potentially lethal manifestations of covid-19.

Presumably few of us are smokers; smoking seriously degrades the ability of the lungs to mount an immune response. Smoking also damages cilia. ncbi.nlm.nih.gov

Indoors v outdoors

In the years before the discovery of antibiotics, one of the mainstays of treatment of respiratory infections was exposure to fresh air and sunlight. The mechanism was a mystery at the time and remains a matter of speculation. The potent antibacterial and antiviral effects of sunlight probably contributed.  Another likely contributing factor was the beneficial increase in synthesis of vitamin D due to sunlight falling on exposed skin.
Vitamin D not only keeps bones, teeth and muscles healthy, but also promotes healthy immune function. Vitamin D can be derived from dietary sources, but at least in the months April-September in the UK, an adequate amount can be derived from sunlight. The duration of exposure required depends on skin colour and amount of exposed skin. In summer, 15 minutes of exposure of arms, legs, abdomen and back to sun is generally adequate. When wearing a top, the duration of exposure must be increased by an amount proportional to the reduction in area of skin exposed.

For these reasons, outdoor exercise is likely to be preferable to indoor exercise, if it is feasible

Psychological stress

Many studies have reported that the combination of emotional stress with the physical stress of running increases the release of the stress hormone, cortisol, and hence is likely to add to the disruption of immune function produced by heavy exercise. academic.oup.com

Cumulative heavy exercise

The potential decrease in immune function produced by heavy exercise is compounded by repeated bouts of heavy exercise. Most of us are aware of the need to avoid repeated demanding training sessions. There is a low probability that we will be drawn into such a pattern of training when the majority of major races have been cancelled or postponed. However if you are inclined to continue a strenuous training program, there is greater need than ever to monitor for signs of over-training at this time. Elevated resting heart rate is one sign, though in fact it is not a reliable sign. One of the most reliable signs of over-training is a deterioration in energy levels, mood and sleep. ncbi.nlm.nih.gov

I hope you all keep well!

Edit, 20 March 2020: Following the very helpful comment by David Dunbar (see below) I wish to add two points:

First, the data that strenuous exercise can reduce immunity in humans still a topic of debate. David provided the link to the paper by Campbell and Turner published last year. That paper provides a useful, up-to-date discussion of some of the evidence regarding exercise and the immune system.  I think the title of the paper which refers to debunking the myth of exercise-induced immune suppression is a little misleading.  Campbell and Turner discuss the positive effects of exercise on immunity. I agree with the points in their discussion. It also examines the studies that report increased respiratory illness following strenuous exercise and points out that several of these studies have weaknesses.  I also agree with most of that discussion. That is the reason why I started with the studies of controlled investigations of exercise and immunity in animals rather than the evidence from observational studies of athletes. Some of the animal studies do report that exercise during the incubation period increases the severity of the infection.   That is a major reason why I consider that we should be cautious in the era of covid-19, and in particular, we should monitor carefully for over-training if we wish to pursue a strenuous training program.

Secondly, with regard to the risk that strenuous training might reduce immunity in athletes, the majority of the evidence indicates that prolonged, demanding exercise is more likely to suppress immunity than short intense exercise. However, this evidence is still debateable. This is why I consider that monitoring for over-training in the most important thing.