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Fighting off infections: strong vs weak immunity differences


Did you know that something as simple as one bad night’s sleep could weaken your ability to fight off an infection? Or that exercising for 150 minutes a week will strengthen your ability to do so?

Your lifestyle choices evidently inform your immune system’s ability to seek out and destroy infections; and, as the cold and flu season takes a hold, your habits will play an essential part in keeping you healthy.

If you always sleep well, get plenty of exercise, and eat a healthy whole food diet, you should be rewarded with a strong immune system – and you’ll know this is the case if you come into contact with a cold, but shake it off easily.

Conversely, if you’re constantly under stress, snatching fast food meals on the hoof, sleeping poorly, and never finding the time to exercise, you could be in for a cold-riddled winter.

But could your health surprise you? Could you lead an apparently unhealthy lifestyle, yet have robust defences? Or could you look and feel the picture of health, yet fall at the first winter flu hurdle? And – critically – is there any way you can determine the true strength of your immunity before that first virus of the season comes your way?


Strong or weak – can you spot the difference?

Nearly every bodily system has clear signs of strength or weakness – you don’t have to wait for ill health to strike to know if your eyesight and hearing are good, your heart and muscles are strong, and your intestines are doing what nature intended.  But the strength of your immune system is different. What you may imagine to be clues about its condition are misleading. The truth is that you have no way of knowing for sure how well it will cope with an infection until it is called on to do so, according to Dr Natalie Riddell, lecturer of Immunology at Surrey University.

Even then the response may not be what you expect. For example you may imagine that feeling unwell after a vaccination is a sign of a struggling immune system, says Dr Riddell. “But in fact it shows that your immune system is strong. Your symptoms indicate that you are reacting to the mock infection introduced by the vaccine and should now recognise and repel the actual infection if you encounter it again.”

Similarly, you may suspect that episodes of low mood and low energy are signs of a weaker immune system, but again the opposite is more likely to be true. “This kind of sickness behaviour is a primitive reaction to infection. It shows that your body is responding correctly to messages between your immune and endocrine systems, which demand that it slows down in order to conserve the energy it needs to mount its immune response and speed up recovery.”

Remember too that the strength of your own immune system is as individual as you are.  Dr Riddell explains. “I may be able to resist infection A, but not infection B.  You, on the contrary, may easily fight off infection B, but not infection A. Our immunity is determined by its history. I resist infection A because I have encountered it in my past, but infection B is completely new to me. My body’s defences swing into action to fight it, and I know that my immune system is strong and working the way it should.

“Every time your body fights off an infection, it creates new antibodies specific to that infection, so that its defences are better prepared for the next time you encounter them. But, if it takes longer than the usual one to two weeks to recover, your immune system is showing signs of weakness.”


Weakest links

These signs of weakness become more likely as you age, says Dr Riddell. “Your immune memory – the part of your immune system that is normally quick to fight off any viruses it has encountered in the past – becomes less effective as you get older. It also struggles to build new immune memory, so your body is less able to remember new infections and recognise them if they strike again. As a result, you’re more vulnerable to circulating viruses than you were as a younger adult. This is also why vaccines do not work so well in older adults.”

But, whatever your age, stress can have the same effect – essentially ageing your immune system to the extent that you could have the increased incidence of colds and other infections normally seen in a much older person.  “That’s because the hormones cortisol and adrenaline, which we release under stress, alter the number of immune cells in our blood and affect how well we respond to an infection,” says Dr Riddell.


While you may not know until you catch a cold how strong your immune system will prove to be, the following tips will at least help to shore up your defences.


. Improve your sleep hygiene

 Many studies have shown the importance of sleep in determining how well you will be able to resist and fight infections. In fact, one study found that just one night of poor sleep – sleeping for six hours instead of the usual seven or eight – significantly reduced immune functioning compared to those who had enjoyed a good night’s sleep.1


. Get enough exercise

Ensuring that you participate in enough exercise each week can help to give your immune system a boost. One study found that the combination of low intensity, high volume exercise and moderate-intensity continuous training (three times a week for 10 weeks) improves our immune response to bacteria. 2  Exercising regularly can also help to protect your body on a genetic level by lengthening your telomeres — the protective caps at the ends of your chromosomes, according to Dr Riddell.  She says: “Telomeres work like the sheaths that protect the end of your shoelaces.  The longer they are, the healthier they will be, and the stronger your immune system as a result”.  If you’re looking to improve your immune response by becoming more active, it’s recommended that you spend 150 minutes cycling or walking every week, alongside muscle strengthening exercises on two or more days.3


. Maintain your gut health

Scientific research has investigated the link between gut bacteria and immunity.  “Your gut microbiome – the balance of different types of bacteria – changes with age, and this is another way in which your immune system can be affected,” explains Dr Riddell. “Research has found that eating more fibrous foods (especially raw fruit and vegetables) helps to increase levels of healthy bacteria, and high levels of these are linked to improved immune responses.”



If you’d like to learn more about how to improve immune health, take a look at our dedicated immune health hub.



  1. Daniel J. TaylorKimberly KellyMarian L. Kohut, and Kai-Sheng Song (2017). Is insomnia a risk factor for decreased influenza vaccine response? Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5554442/
  2. David Bartlett, Sam O. Shepherd, Oliver J. Wilson, Ahmed M. Adlan, Anton J. M. Wagenmakers, Christopher S.Shaw, and Janet M. Lord (2017). Neutrophil and Monocyte Bactericidal Responses to 10 Weeks of Low-Volume High-Intensity Interval or Moderate-Intensity Continuous Training in Sedentary Adults. Oxidative Medicine and Cellular Longevity Volume 2017, Available at: https://doi.org/10.1155/2017/8148742
  3. NHS Guidelines (2018). Physical Activity Guidelines for Adults. Available at: https://www.nhs.uk/live-well/exercise/


Karen Evennett

Surrey-based B2C copywriter with 3 decades of writing for national magazines.


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