How Running Boosts Your Immunity

Has there ever been a better time to protect yourself from illness? We didn’t think so

THERE’S NO QUESTION THAT running offers a range of health benefits – it keeps your heart and lungs strong, helps you drop pounds or maintain a healthy weight and is a great way to de-stress. But when it comes to supporting your body’s defences against infection, experts are still debating whether exercise can suppress the immune system, making runners more susceptible to infection after a workout.

Researchers look at the effect of exercise on the immune system in the short term (a single bout of exercise) and the long term (days, weeks, months and years of regular exercise), says exercise physiologist Dr James Turner, a senior lecturer at the University of Bath and a specialist in immunobiology.

When you start your run, your heart rate increases because of adrenaline and more blood moving through your body. Your body calls on certain types of white blood cells – your body’s immune-system cells – to race around and fight off potential pathogens. ‘Within seconds of starting to exercise, your immune cells increase, double, triple and some even increase tenfold,’ says Turner.

So far so good, and about 10-15 minutes after finishing a workout – whether it be low- or high-intensity – that immune cell count goes back to normal. But then, Turner says, some of those immune cells decrease to below normal levels – sometimes by half or more – for hours before returning to the normal baseline level.

This is what’s known as the ‘open window,’ says Dr Caroline Jouhourian, a gastroenterologist at Lowell General Hospital in Lowell, Massachusetts, US.

And, until recently, it was widely accepted that during that open window, the immune system was suppressed, leaving people – that’s us runners – more susceptible to picking up an infection. •

But researchers, including Turner and his colleague Dr John Campbell, point out that those immune cells haven’t disappeared during that open window, they’re just in the bloodstream looking for infection – which is, Turner says, what they should be doing. That process is called immune surveillance, and exercise such as running can make it happen more quickly and efficiently.

THE LONG GAIN

When it comes to the effects of exercise on the immune system over the long term, there is an advantage to lacing up regularly. ‘Long-term exercise and training encourage a healthy, anti-inflammatory environment [in the body],’ says Turner. There’s no question that the immune system weakens with age, but running might slow down the ageing process. Specifically, it seems to strengthen the adaptive (or acquired) immune system, says Jouhourian.

The adaptive immune system is learned over time, meaning it creates antigens to fight specific infections. A 2018 study, published in Aging Cell, found that cyclists between the ages of 55 and 79 had less immunosenescence – the medical term for immune-system deterioration associated with ageing – than adults in the same age group who did not exercise. What’s more, the researchers found that the older, more active subjects produced the same number of immune T cells (a type of white blood cell) as a 20-year-old. That means, Turner says, older adults who are regularly active might respond better to vaccines. A paper published in Brain, Behavior and Immunity supports this idea: Short workouts and long-term exercise significantly augment the immune response to vaccination.

But can you have too much of a good thing? Overtraining can lead to a host of problems, including injury and burnout. But while the received wisdom has been that it can leave your defences weakened, whether it actually makes you more susceptible to

illness is still up for debate and, in fact, recent evidence suggests that it doesn’t.

But how you recover is key, says Jouhourian, pointing out that refuelling properly plays a key role in staving off illness and injury. ‘Nutrition is really important,’ she says. ‘Your immune system requires vitamins and minerals to function properly.’ Rest is important, too – if you only slept two hours, exercise is probably not beneficial, she adds.

RISK AND REWARD

You may have read that elite athletes – who undergo intense long-term training and competition – might suffer from increased rates of upper respiratory infections (or URIs), but experts are now also calling that thinking into question. ‘We’re still not 100 per cent sure if you can exercise too much,’ says Turner. ‘We don’t dismiss the possibility that elite athletes are at greater risk [for developing illness], but that’s probably not because their immune systems are suppressed.’

In a debate paper published earlier this year in Exercise Immunology Review, Turner and Campbell point out that while athletes participating in a large marathon, for example, might report experiencing higher levels of URI symptoms, these cases are often not confirmed with laboratory tests. People may think they have a cold when it’s actually allergies or some other noninfectious issues that have similar symptoms, says infectious-disease specialist Dr Amesh Adalja, a senior scholar with Johns Hopkins Bloomberg School of Public Health in the US.

When infections do occur, experts now point to other factors – some of which we have all become very keenly aware of in recent months – besides compromised immune function as potential culprits. ‘What is now very clear is that it’s not exercise suppressing the immune system; it’s thousands of people taking part in a marathon and inhaling droplets, touching surfaces and not eating or sleeping well,’ says Turner.

The number-one risk factor for coming down with an illness is exposure, says Adalja. ‘Remember, a virus has to get to you from somewhere,’ he says. ‘Any type of social interaction in which you’re in contact with a virus – travel, other people, improper hygiene during a race like spitting or sharing water bottles – makes it more likely for you to come into contact with it.’

Keeping these factors in mind when you return to organised running events is key to reducing your risk of infection, but in the meantime, the good news is that the latest science shows clocking the miles will boost your body’s defences.