James Hewitt
981 words
4 minutes

Can’t boost immune system, but can suppress it

In recent weeks, I’ve noticed a significant rise in the number of supplements and techniques claiming to ‘super-charge’ the immune system. Unfortunately, most of these claims are misleading and unfounded; we can’t boost our immune system. However, we can suppress it, so here are some evidence-based ways to maintain and avoid putting unnecessary strain on your immune system.

What Is The Immune System?

Our immune system is a complex network of structures, organs, tissues, and specialised cells that fight infection, including:

  • White blood cells
  • Antibodies
  • The complement system (which enhances the ability of antibodies and phagocytic cells (cells which ‘eat’ foreign particles) to clear microbes and damaged cells.
  • The lymphatic system
  • The spleen
  • The thymus.

These parts of the immune system operate in harmony to hunt and destroy harmful pathogens (anything that can produce disease), such as viruses. ‘Boosting’ this process could actually be detrimental – as is evident in auto-immune disorders which are associated with an over-active immune system. Ideally, we should aim to make decisions and adopt behaviours which enable our immune system to function normally, in a healthy range.

Sleep – Avoid Screwing Up Deep Sleep

Our sleep and circadian rhythm (body clock) has a powerful influence on immune function. Sleep appears to play a specific role in the formation of ‘immunological memory’ (the ability of the immune system to recognise a foreign substance, such as a bacteria or virus, that the body has previously encountered, and activate an immune response)2.

The critical role that sleep plays in immune function also seems to be associated with slow-wave NREM sleep (deep sleep). Most slow-wave NREM sleep occurs in the first part of the night, so it’s particularly important to avoid actions which can compromise sleep early on, such as consuming caffeine later in the day, as I wrote about, here.

Ten tips to improve your sleep include:

  1. Adopt a consistent sleep/wake time to avoid disrupting your body clock.
  2. Stop caffeine as early as possible.
  3. Stop drinking alcohol as early as possible (as I wrote about here)
  4. No napping later than 3pm.
  5. Prioritise exposure to bright natural light in the morning (even if you have to just sit next to a window).
  6. Minimise screen exposure (and turn down brightness) in the hours before sleep.
  7. Ensure your bedroom is as dark as possible.
  8. Keep your room temperature ~18°c.
  9. Choose bedding/clothing which will minimise overheating.
  10. Aim for at least 7 hours of sleep.


When we’re exposed to brief stressors, the immune response is upregulated, likely as a way to prepare the body to defend itself in the event of an injury. However, persistent stress is associated with suppression of the immune system.1 Our attitude toward stress makes a difference, though. We can learn to manage stress and minimise these potential adverse effects. In this article, I wrote about which stress reduction techniques appear to be the most effective.

Nutrition – More Does Not Necessarily Mean Better

Concerning particular foods and immune function, as I wrote in this blog about nutrition and cognitive performance, more does not necessarily mean better. While a nutrient deficiency may be associated with depressed immune function, if an individual is consuming an adequate amount of nutrients, mega-dosing on a particular food or vitamin is not going to offer any additional benefits. As a practical place to begin, try to fill half your plate with vegetables at your main meals, featuring at least three different colours (e.g. green leaves, orange carrots and red peppers).

Exercise Like Goldilocks

The weight of evidence suggests that regular physical activity and frequent exercise could enhance immune function and even delay the ageing of the immune system3. However, unusually hard, continuous, prolonged efforts, such as a tough training session that you have never done before, may lower the body’s resistance to infection. Contrary to popular belief, this is not because the immune system is suppressed by exercise. In fact, the immune system response is heightened after exercise, it’s just that its activity is redistributed to the tissues which have been working hard during exercise.

While it’s not a perfect model, the relationship between exercise and risk of infection can be described as a J-shaped curve4.

Moderate regular exercise likely represents the ‘just right goldilocks’ zone for exercise. The natural next question, though, is ‘what is moderate and regular’? The answer is that this varies depending on your habitual exercise patterns. If you are aiming to maintain healthy immune function, such as during a pandemic, avoid suddenly and significantly ramping up your training intensity and volume.

I live in France and this country, like several others, has mandated that everyone stay in their homes. Cycling outdoors is banned. It may seem that this would limit the risk of significantly increasing training load. However, this may not be the case. I know several cyclists who are stuck at home and, rather than following their usual diet of low to moderate intensity outdoor rides, they are now smashing out high-intensity training sessions several times each week, on indoor trainers.

As is the case with many aspects of human physiology, large, fast changes in any direction are rarely beneficial. If you exercise regularly, try to find a way to keep going, even if you are stuck inside. If you haven’t exercised regularly for a long time, it’s probably a good idea to start exercising, but build up gradually.

Beware The Bro-Science

As is often the case in the field of human wellbeing and performance, the most effective techniques usually turn out to be the most basic. So, save your time and money and forget about the latest immune-boosting supplement or esoteric method. Aim to sleep at least 7 hours per night, with regular bed-times, try to manage your stress, eat a nutritious, varied diet and exercise regularly. Simple.


  1. Segerstrom SC, Miller GE. Psychological Stress and the Human Immune System: A Meta-Analytic Study of 30 Years of Inquiry Suzanne. Psychol Bull. 2004;130(4):601–30.
  2. Besedovsky L, Lange T, Born J. Sleep and immune function. Pflugers Arch Eur J Physiol. 2012;463(1):121–37.
  3. Campbell JP, Turner JE. Debunking the myth of exercise-induced immune suppression: Redefining the impact of exercise on immunological health across the lifespan. Front Immunol. 2018;9(APR):1–21.
  4. Nieman DC. Exercise, infection, and immunity. Int J Sports Med (1994) 15(Suppl 3):S131–41. doi:10.1055/s-2007-1021128

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