How Exercise Can Help You Fight The Flu, Boost Immune System

The flu season is well and truly among us. Many people go out and get a flu shot in the hope that the vaccination will protect them, but how effective is it really?

According to the Centers For Disease Control and Prevention “Recent studies show that flu vaccination reduces the risk of flu illness by between 40 per cent and 60 per cent among the overall population during seasons when most circulating flu viruses are well-matched to the flu vaccine”.

But what if the viruses circulating throughout the population are not well-matched to the vaccine? Well, put simply, the level of protection is significantly reduced. But just because we get exposed to a pathogen (virus or bacteria) doesn’t mean we are guaranteed to get infected from it. A healthy immune system should provide a line of defence which can attack and destroy foreign invaders before they take over and make us sick.

So, assuming the vaccination is lacking efficacy, there may be a natural solution to the problem. A healthy lifestyle is a great way to boost immunity and reduce the risk of getting the flu. It is commonly known that healthy nutrition, sleep, and stress management all improve immune function, but what about exercise?

Just because ‘some’ is good doesn’t mean ‘more’ is better

Exercise has been shown to be a potent immunogenic stimulus. In other words, it helps to build a robust and effective immune system, but the dose is very important. Moderate regular exercise has been shown to reduce one’s susceptibility to common upper respiratory tract infections (URTI). However, long, intense exercise can actually have the opposite effect and increase URTIs.

Overtraining/under-recovering can lead to a weakened immune system, ultimately increasing the risk of getting the flu. After very strenuous exercise you are actually more vulnerable to bacterial/viral illness and infection due to a temporary reduction in immune system function. Continuous and prolonged exercise for more than 90 minutes of moderate-high intensity seems to cause the greatest post-exercise immune system depression.

Over-exercising, such as chronic cardio (long-distance running day after day after day), combined with inadequate sleep, poor nutrition and high-stress levels is a bad idea during the flu season. This is why it’s so common for elite athletes to get sick during a difficult training camp in preparation for competition. Their immune system weakens as the duration and intensity of their sessions ramp up over time, hence why an intelligently and effectively designed periodised training program is so important.

Aim for the minimum effective dose i.e just enough exercise to strengthen your immune system but not too much to weaken it. Getting the optimal daily dose of exercise is a critical part of the equation and will require a sense of personal intuition and really listening to your body.

What about staying out of the cold?

You’ve probably heard the age-old saying; ‘stay warm you don’t want to catch a cold’, right?

Well, research has been unable to prove this statement to be completely true. For the average healthy person, the idea that the cold makes you sick is largely a myth. The truth of the matter is, certain viruses survive and spread more easily in cold temperatures, plus we spend more time indoors and are at close contact with more people which can increase the likelihood of infectious pathogens being transmitted, but it is not the cold itself that makes people sick.

It is very important to distinguish between correlation and causation. Just because cold weather is associated with more sickness doesn’t mean the relationship is cause-and-effect. However, there are exceptions. Special population groups such as the elderly and those with known chronic respiratory conditions like asthma tend to be at higher risk of pathogenic infections during cold weather.

Interestingly, cryotherapy (cold therapy) such as cold-water immersion, ice baths, cold showers, and full-body cryotherapy chambers have been shown to boost immune system functionality.

Exercise and cold exposure are both forms of hormesis or hormetic stressors ie. a low-dose, acute exposure of a stimulus/stressor that elicits a healthy response by the body such as improved immune function. But high-dose, chronic exposure of the exact same stressor can have the opposite effect i.e reduced immune function.

Stress is not necessarily something we should fear or avoid. It can be good or bad for you depending on the dose and duration. The goal is not to be stress-free – the goal is to be stress-fit!

On a personal note, I swim in the ocean every day of the year (including cold winter mornings) and I also exercise every day. The dose of both stimuli is enough to stimulate a healthy hormetic response but not enough to make me sick. I haven’t had a common cold or flu in nearly three years so I guess it’s working for me.

If you’re a regular healthy person with no known chronic respiratory diseases, you don’t have to avoid getting cold and you certainly don’t have to avoid exercise – just get the dose right.

The takeaway

So, whether or not you’ve had the flu shot this year, exercise is a wonderful tool to add to your toolkit this winter to help build a strong, efficient immune system, but don’t overuse it.

If you really want to make a difference to your flu-fighting capacity, exercise regularly at a moderate intensity and don’t forget to combine it with adequate sleep quality and quantity, as well as a highly nutritious and nourishing whole-food way of eating.

Whether it’s full body circuits, yoga, pilates, brisk walks in nature, resistance training, HIIT or standard cardio, just keep moving this winter and give your immune system the stimulus it needs to get stronger and ultimately build you into a flu-fighting machine.

Drew Harrisberg is an exercise physiologist and diabetes educator

Want more expert advice on how to get healthy over winter? Look no further than’s Hit Refresh 2019 Winter Edition, which runs for the whole of July. You’ll find smart tips and action plans for refreshing your nutrition, fitness, mindset and beauty… and much more!

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