Exercise has a profound and lasting positive effect on your immune response and may be one of the single most effective things you can do to stay healthy long-term. In fact, a study has found daily moderate exercise can reduce your risk of upper respiratory tract infection by around 50%.
Not only do people who exercise regularly experience fewer sick days, they also suffer milder symptoms of disease when they do get sick. Research shows this is true across gender, age and body size.
Want to learn more? Check out our guide on diet, exercise and the immune system!
Imagine you pull on your running shoes early morning and step out in the cold winter rain and start pounding the pavement. Instinctively, this sounds like a recipe for getting sick, right?
It really is a recipe for protecting your body against disease. Exercise is like a kick-start for your immune system and during a training session your blood is flooded with immune cells which circulate around the body looking for and killing off unwanted substances. After the training session, the immune cells move from the blood and congregate in the organs and tissue that are most sensitive to infection – like your upper respiratory tract and your lungs – creating an extra protective layer against disease.
For a long time, scientists interpreted the reduction of immune cells in the blood after exercise as something bad and the effect became known as the open window hypothesis – the theory being that the body was left unprotected against disease after exercising. But today we understand this effect as just another clever way for the body to protect itself.
The more often you exercise and allow your body to trigger this immune response, the more often you will gain the benefit of this extra protective layer – possibly up to a certain point, as you’ll see further down.
This is true even when you're not feeling well! If you have a bit of a cold, you're better off going for a walk to get the blood flowing than sitting at home waiting it out. This, of course, depends on the severity of your symptoms but staying active while unwell can help you recover more quickly.
One study showed that people who take 3,000 steps per day have significantly more inflammation in their body tissue than people who make it to 10,000 steps per day. Inflammation is itself an immune response but when you have chronic low levels of inflammation your body is not as able to respond to disease.
Being active every day generally results in better sleep at night which gives your body more time to suppress inflammation and keeps your immune system from having to work overtime.
During and after moderate exercise stress hormones are also lowered and these hormones can suppress immune cell function. It's easy to tell someone to stress less and much harder to actually do it but sleeping better can alleviate your stress symptoms.
Athletes tend to report more symptoms of disease than people who undertake moderate exercise and studies with endurance athletes show an increased risk of illness in the time after a competition event. It's worth noting, though, it is unclear whether this is due to changes in the immune response or factors such as greater exposure to pathogens, travel, stress or other outside factors.
The Australian Government guidelines recommends getting 300 minutes (5 hours) of moderate exercise or 150 minutes (2.5 hours) of intense exercise every week – or a combination of the two. If you're unable to exercise that much, some exercise is almost always better than no exercise.