Can exercise make you sick? Exercise & the immune system

Are you coming down with every cough and cold around? While exercise can be beneficial for your immune health, more is not necessarily better. Nutritionist Christine Bailey explains how intense exercise can make you sick, before revealing how to eat and work out to support your immune system.

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We all know that exercise brings a lot of health benefits, but did you know it can also enhance your immune health? When you exercise, certain types of white blood cells, such as neutrophils and lymphocytes, circulate at a higher rate than normal to help detect and destroy pathogens.

If you exercise regularly, you’re likely to reduce your risk of infections, compared to being inactive. One study published in the British Journal of Sports Medicine found people who exercised for at least 20 minutes a day, five or more days per week, reported 43 per cent fewer days with upper respiratory tract infection symptoms than those who were sedentary.

But more is not always better. Periods of intense training have been associated with increased risk of infection, due to a temporary depression of white blood cell functions. Known as the ‘open window’ hypothesis, these immune changes could make you more prone to infections, especially if you’re not paying attention to proper rest and nutrition.

Marathon and ultra-marathon runners are often more prone to respiratory infections during the days following a race. More generally, any prolonged bouts of strenuous exercise, particularly those lasting over 90 minutes, can temporarily suppress your immune function, which can potentially make you sick. This effect may last at least 24 hours.

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How can exercise make you sick?

What’s at play? The causes of immune depression are likely to be linked to increases in stress hormones and changes in inflammatory signalling chemicals. Intense training also suppresses Secretory IgA (SIgA). SIgA plays an important role in protecting
the mucous membranes of your respiratory tract, gut and even your bladder from infection. This is one of the reasons why athletes appear to be at a greater risk of respiratory and gut infections.

Of course, there are many other factors to consider that will impact your immune health. For example, mental stress, lack of sleep, insufficient recovery time and low levels of certain nutrients can make you more susceptible to infections. Depending on where you train, you may also be at increased risk of exposure to pathogens in the environment (crowded gyms and using shared equipment, for example, can have this effect).

Plus, a higher rate and depth of breathing can potentially mean breathing in more bugs. Intense training can also increase gut permeability, which may make you more prone to infection and digestive problems.

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How to support your immune system:

Nutrition, as well as drinking plenty of fluids, plays a key role if you’re looking to prevent infections and recover quicker. Protein is vital for a healthy immune response, and adding sufficient carbohydrates has been shown to blunt the inflammatory effects and reduce the risk of infection after training. If you are struggling with ongoing infections, make sure you are consuming enough calories overall. Being in a calorie deficit for too long or crash dieting can reduce your ability to fight infections.

Eat a variety of colourful plant-based foods

When planning each meal, look to include plenty of colourful fruits and vegetables. Not only are these a great source of immune-supportive vitamins such as vitamin C and vitamin A, but they also contain a wealth of antioxidants (including flavonoids and quercetin) shown to support immune health. Spices such as garlic, ginger and turmeric are great immunity supporting additions to meals due to their anti-inflammatory benefits.

Both blackcurrant and elderberry extracts have been shown to aid recovery after workout and to support immune function. Beta glucans, present in foods such as oats, mushrooms and barley, may also help your immune system fight against bacterial and viral infections. Certain green superfoods such as chlorella have also been shown to support athletes’ immune health, in part through their ability to increase SIgA levels.

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Top up your vitamin D levels

Vitamin D is one nutrient where supplementation (at least 800ius) is advised over the winter months. Certain foods such as oily fish, fortified foods, eggs and mushrooms do provide some vitamin D, but it is unlikely to be sufficient during the winter (as the main source of vitamin D is through sunlight). Zinc is another micronutrient that’s crucially important for a healthy immune response, so eat more zinc-rich foods including meat, fish, dairy, beans, nuts and seeds.

Learn more about how to increase your vitamin D levels naturally

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Feed your gut

When it comes to overall immune health, remember the importance of your gut. Having a diverse range of microbes has been shown to be beneficial for health, including immune function. Try to include fermented foods such as yoghurt, kombucha, kimchi, kefir or sauerkraut daily. In addition, certain probiotic supplements, such as saccharomyces boulardii, have been shown to raise levels of SIgA, making them particularly useful against respiratory infections.

Another useful supplement for both performance and immune support is bovine colostrum. Rich in polypeptides, lactoferrin and immunoglobulins, colostrum has been shown in studies to support immune health and reduce both respiratory and gut infections.

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Reduce stress and stay hygienic

Taking steps to prevent an infection will also mean paying attention to various lifestyle factors. Managing stress, ensuring sufficient sleep and factoring in rest periods after intense training is essential. Remember the importance of good personal hygiene, and avoid contact with anyone who is infected.

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