Support your immune system
Exercise can build strength and help fight disease – so why do so many fitness fans get ill? Here’s how to work out to your immune system’s advantage
W ith gym doors open and sports clubs welcoming members back, you may be wondering whether it’s safe to attend exercise sessions with others – but keeping fit could be a really good way to bolster your immune defence. Indeed, evidence supports physical activity as a preventive measure against severe Covid-19 infection. The study published in the British Journal of Sports Medicine shows that patients who had Covid-19 and had been consistently inactive during the previous two years were more likely to be admitted to hospital, to require intensive care, and to die than were patients who had consistently met physical activity guidelines. ‘Exercise boosts your circulation so that millions of white cells enter your blood stream, enhancing your body’s surveillance so it can better detect harmful micro- organisms,’ explains
Professor Michael Gleeson, emeritus Professor of Exercise Biochemistry at Loughborough University, and the author of Eat, Move, Sleep, Repeat.
Exercise also has an anti-inflammatory effect. ‘Another benefit of regular exercise and being reasonably fit is that it helps to keep us lean by burning calories and, most importantly, it dampens down inflammation – the thing that can generate severe health problems during Covid-19 infection,’ adds Gleeson. ‘In contrast, if you’re sedentary and overweight, your adipose (fat) tissue becomes inflamed and you develop what is called chronic low- grade inflammation, which primes your body to produce an excessive pro-inflammatory response to infection and tissue damage.
That is just what you don’t want if you get infected with Covid-19.’
THE FIT FORMULA
However, while research confirms that regular moderate exercise can cut your risk of sickness in half, further studies show that strenuous exercise such as marathon training or excessive amounts of gym or cardio work can increase it. The main culprits? Upper respiratory tract infections (URTIS), such as coughs, colds, sinusitis and tonsillitis. The average adult has between two and four URTIS every year, and these infections are prime causes of illness among seasoned athletes. In fact, an analysis of athletes at the 2011 World Championships in Daegu, South Korea, discovered that over 40 per cent of reported illnesses were upper respiratory tract infections, with those taking part in the marathon, 20K race walk or 50K race walk most likely to fall victim to the sniffles. What’s the conclusion? Intense workouts, extreme training schedules and regular racing can suppress the body’s immune response.
‘If you regularly do moderate exercise without trouble – let’s say, cycle at 50 per cent of your aerobic capacity for an hour several times a week
– it won’t have much of an impact on your immune system. In fact, it’s probably good for it,’ explains Gleeson. ‘But exercising for 90 minutes to two hours at an intensity above 70 per cent of your aerobic capacity will make you
vulnerable to illness.’
THE EXERCISE EFFECT
Why do sweaty sessions chip away at your defences? Well, strenuous exercise, such as training for an
‘Regular moderate exercise can cut your risk of sickness’
endurance event, has been shown to suppress NK (natural killer cell) activity. And intense activity can be psychologically stressful, too.
HOME IN ON HORMONES
Mental strain increases levels of the stress hormone cortisol which, teamed with another exercise-induced stress hormone, adrenaline, down regulates white blood cell function and causes a decrease in immunity. ‘Physical stress, such as that experienced on a long run, can cause a one- off dip in the immune system that suppresses it for a day or so,’ says Gleeson,
‘Physical stress can cause a one-off dip in the immune system that suppresses it for a day or so’
‘but repeated or chronic psychological stress seems to impact the immune system the most.’
These effects are short-lived however. Indeed, experts note that your immune system will regain full strength after a brief window of time following race day. ‘In most cases, the window in which immunity is suppressed lasts for 24 hours,’ adds Gleeson, ‘but the time does vary because some cells are affected more than others.’
Endurance competitors, such as marathoners and triathletes, can expect every aspect of their immune system to take a blow for at least three to six hours after crossing the finish line, with most racers being vulnerable to infection for a day or two afterwards. During this time, it’s wise to support your system by getting plenty of sleep, eating well, resting up and avoiding contact with crowds.