If you sleep well, get plenty of exercise, and eat a healthy, wholefood diet, you should be rewarded with a generally strong immune system. Conversely, if you're constantly under stress, sleep poorly and regularly eat fast food without finding the time to exercise, you place yourself at a higher risk of catching an illness or infection. To determine the true strength of your immune system, we've put together this guide to understanding and improving your immunity.
Strong or weak – how to spot the difference
Almost every system in the body has a clear way of indicating whether it is functioning correctly. You don't always have to wait for illness to determine whether your eyesight and hearing are in good health, or your joints and muscles are strong enough. But the strength of your immune system is different. Speaking to Healthspan, Dr Natalie Riddell, lecturer of Immunology at Surrey University, states that you'll often have no way of knowing how well your body will cope with an infection until it becomes affected.
For example, Dr Riddell states that some patients believe that feeling unwell after a vaccination is a sign of a struggling immune system, while in fact this is a sign that your immune system is functioning well. Experiencing mild symptoms after a vaccination indicate that your body is reacting to the mock infection and should be able to recognise and tackle a stronger form of the pathogen when encountered 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. In fact, Dr Riddell states that "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."
It's also important to remember that the strength of an immune system depends both upon the individual and the type of infection they come into contact with. Dr Riddell explains, "one person may be able to resist infection A, but not infection B. On the contrary, someone else may easily fight off infection B, but not infection A.
"Our immunity is determined by its history. Each 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 you take longer than the usual one to two weeks to recover, this can be a sign of a weak immune system."
Signs of weak immunity 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 becomes more difficult to add to your 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 one of the reasons why vaccines tend not to work as well in older adults."
However, regardless of age, stress can always have a detrimental effect on your immune system. In fact, continued exposure to stress can age your immune system, making you more vulnerable conditions usually found in much older people, such as the increased incidence of colds and other infections. Dr Riddell explains that this is "because stress hormones such as cortisol and adrenaline alter the number of immune cells in our blood and affect how well we respond to an infection."
How to improve your body's natural defences
While there is no simple way of improving your immune system, there are a few measures you can take to better prepare yourself for cold and flu season.
1. Increase your quality and quantity of sleep
Many studies have shown that the quality and quantity of your sleep plays an important role 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 immunity, compared to those who had enjoyed a good night's rest.1
2. 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 carrying out a combination of low-intensity, high-volume exercise and continuous training for three times a week improved the body's response to bacteria.2 According to Dr Riddell, regular exercise can also support your immune system on a genetic level by lengthening your telomeres — the protective caps at the ends of your chromosomes.
She explains that "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
3. Maintain your gut health
Since 70-80% of your immune system is found in the walls of the digestive tract, keeping your gut healthy can also have a positive impact on your immune system.4 "The balance of your gut bacteria changes with age, and this is another way in which your immune system can be affected," explains Dr Riddell. She states that "research has found that eating more fibrous foods (especially raw fruit and vegetables) helps to increase levels of healthy bacteria — high levels of which can be linked to improved immune responses."
Making these simple changes to your diet and lifestyle is the best way to start optimising your immune system. If you’d like to learn more about how to keep your immune system healthy, head over to our Immunity Advice Centre.