chapter 9: how exercise benefits your immune system

Exercise is beneficial for both our immunity and gut health. Research in humans has confirmed that exercise increases microbial diversity, and has been shown to decrease inflammation and infection, while promoting recovery and enhancing immune function⁸².

Exercise and the gut

Our gut bacteria play a role in how physical activity can decrease our risk of disease, but the mechanism is not yet fully known. However, exercise has been shown to promote the immune system in positive ways, then, in turn, the immune system sends chemical signals to the gut bacteria⁸³. In addition, physical activity itself can directly affect the composition of the gut bacteria. The short-chain fatty acid, butyrate, is made by our gut bacteria and is very important for our immunity – exercise encourages our bacteria to make more of it⁸⁴.

In a study from the University of Illinois, researchers found that exercising for just six weeks could impact the gut microbiome. The study participants were assigned an exercise programme consisting of cardiovascular exercises for 30–60 minutes, three times a week for six weeks. At the end of the study, the researchers sampled the participants’ gut microbiomes, and discovered that the microbiomes had changed. Some participants experienced an increase in certain gut microbes and others a decrease. Many had an increase in microbes that are involved in the production of beneficial short-chain fatty acids, such as our friend butyrate. After the initial period of six weeks, the participants then returned to six weeks of their normal inactive lifestyle. When the researchers sampled participants’ microbiomes again at the end of this sedentary period, they found the microbiomes had returned to how they were before the period of exercise. This suggests the impact of exercise on the microbiome may be short-lived, hence it appears that exercise needs to be performed regularly.

When it comes to exercise, just as in our diets, we need balance, since too much exercise has been shown to result in temporary gut damage and impaired gut function⁸⁵. This appears to be caused by an increase in body temperature and decreased blood flow. However, physical activity is imperative for health and for the lymphatic system. We need to keep the super-important and immunity-nourishing lymph moving as it contains a significant proportion of our immune cells. As we know, ageing decreases our immune function, and the thymus gland, which produces our T cells, shrinks. However, exercise is one of the most effective strategies when it comes to strengthening immunity, as putting your muscles through their paces, promotes the release of a hormone (IL-7), which helps prevent thymic involution so our thymus can continue to make our important T cells.

In the last few decades, numerous studies have investigated how exercise impacts immunity, and it is commonly acknowledged that regular moderate-intensity exercise has a positive effect on immunity. One study found that 30 minutes of brisk walking increased the circulation of NK cells and white blood cells, and when these immune cells come face to face with a harmful pathogen, they are able to kill it effectively86. However, the researchers reported that about three hours after exercise immune cells head back to the tissues they derived from. So it appears that the immune-supporting effects of exercise may be somewhat short-lived, which is why the ‘regular’ part of regular exercise is so important.

Furthermore, regular physical activity, in the long term, has been shown to delay the changes that occur to the ageing immune system, thereby decreasing the infection risk. A recent 2020 analysis, published in the international journal Exercise Immunology Review, assessed the effect of exercise on our immune function and investigated whether the immune system is impacted positively or negatively after exercise. The analysis determined that, rather than the act of exercising itself, infections are more likely to be associated with poor nutrition, inadequate sleep, stress, travel and, significantly, exposure to pathogens at large events such as marathons⁸⁷.

What exercise is most effective?

For overall health, UK government guidelines recommend that adults aged 19–64 should aim to be active daily. Over a week, activity should add up to at least 150 minutes of moderate-intensity exercise, such as brisk walking, swimming or cycling⁸⁸. Alternatively, comparable benefits can be achieved through 75 minutes of vigorous-intensity activity, such as running, swimming or HIIT, spread across the week. However, 75 minutes or more of intense exercise may be too much for some people, as when you go that long at a high intensity, stress hormones such as cortisol increase, and the immune system does not respond well to that.

Adults should also undertake physical activity to improve muscle strength on at least two days a week. This is particularly important if you practise intermittent fasting. Good examples of this type of activity include weight lifting, yoga, Pilates – or any activity which involves you using body weight or working against a resistance. Even carrying heavy food shopping can be beneficial.

US recommendations as to how much exercise one should be doing per week are similar, with the advice that adults should be performing at least 150 minutes of moderate-intensity aerobic exercise a week, as well as two muscle-strengthening exercise sessions.

• In England, 1 in 4 women and 1 in 5 men are classed as physically inactive – doing less than 30 minutes of moderate physical activity per week.
• In addition, only 34 per cent of men and 24 per cent of women undertake muscle-strengthening activities at least twice a week.

In a study of 150 adults, aged 50 and over, moderate physical activity was shown to significantly reduce the risk of contracting an acute respiratory infection, such as cold or flu. The researchers also showed that severity of an infection was also reduced⁸⁹. Moderate-intensity aerobic exercise, such as walking or cycling, for 30–60 minutes a day appears to be the most effective when it comes to optimizing immune function.

I personally love walking – it is what we were built to do. My great-grandmother lived to 106 and walked at least two miles every day until she was in her late nineties. A 30-minute walk in the fresh air decreases the duration and severity of a mild infection, while stimulating the lymph to do its job properly, in addition to supporting gut health and immunity. It is also a fantastic stress buster, and successful stress management, as we will see in the next chapter, is essential when striving for a balanced immune system.