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What is your immune system and can you strengthen it?

Chopping board of citrus fruit and juice
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The autumn and winter months are a time when more of us get sick with coughs, colds and the flu. Around this time, you might see more adverts for remedies said to “strengthen” your immune system. But is there any truth to these claims? Read on to find out.

The immune system

The label “immune system” is used to describe the defences in the body that help protect us against bacteria, viruses, parasites and other types of germs.

These defences include our skin and the mucous membranes in our nose, mouth, ears, eyes, genitals and anus. The acids in the stomach also protect our bodies by killing off bacteria and other germs.

White blood cells are another really important part of the immune system. If germs get past the first defences listed above, white blood cells will fight the infection.

Certain types of white blood cells known as lymphocytes help to develop immunity to germs by creating antibodies. When we’re exposed to the same germs again, our bodies release the same antibodies, allowing us to fight off the infection quickly and effectively.

Causes of a weakened immune system

As you grow up, your immune system is exposed to more and more germs, and gets better at fighting them off. By the time you’re an adult, you should have a fully functioning immune system that can effectively fight a range of different infections – including those you’ve been vaccinated against.

However, some people may have a weakened immune system due to illness or medical treatment, which means they’ll be more susceptible to infection. You might have a weakened immune system if you:

  • Have HIV
  • Have cancer
  • Are malnourished
  • Are taking certain medications or receiving certain medical therapies, like chemotherapy

There are many different things that can cause your immune system to weaken, but it’s not something that happens overnight, or something that can be quickly remedied.

How to strengthen your immune system

Many vitamins, supplements and health foods claim to “boost” or “strengthen” your immune system, but this isn’t really possible. However, the opposite is true – neglecting your diet and living an unhealthy lifestyle can have a negative impact on your immune system.


If you want to maintain a healthy immune system, make sure you’re eating the kind of varied and balanced diet set out by the NHS Eatwell Guide. This diet has plenty of fruits, vegetables and starchy carbohydrates, and is packed with the nutrients that keep us fit and healthy. Read our healthy eating guide for more tips.


Vitamin D is an essential nutrient for the immune system. Although we can get vitamin D through our diet, we generate most of it through exposure to sunlight. To learn more about getting vitamin D safely without risking sun damage and skin cancer, read our blog vitamin D for different skin types and ages.

Outside of the spring and summer months, when the sunlight is too weak to generate vitamin D, the NHS recommends taking 10 micrograms (mcg) of vitamin D supplements each day. You might need to take these year-round if you spend most of your time inside, or cover most of your skin with clothing when you go outside.

Shop immunity


If you struggle to eat the kind of diet set out by the NHS, you might benefit from taking supplements. Other than vitamin D supplements, your immune system could benefit from the following:

  • Vitamin A
  • B vitamins (B6, B12 and folate/folic acid)
  • Vitamin C
  • Iron
  • Selenium
  • Zinc
  • Copper

To find out how much of these you need each day, read this guide from the NHS, making sure that you check the recommended upper limit for each vitamin. As an example, adults need 40 milligrams (mg) of vitamin C each day, and shouldn’t take daily supplements of more than 1,000 milligrams (mg).

Remember: there’s no harm in taking supplements, but you probably won’t need them if you’re eating a healthy, varied and balanced diet. It’s always best to speak to your GP or a pharmacist first.

Nutri Within vitamin finder


Missing out on a good night’s sleep every now and then isn’t a problem – but if it happens regularly, your immune system could suffer. If you struggle with sleep, try making some simple changes like avoiding caffeine and screens before you go to bed, and making your bedroom darker and quieter. More tips can be found here.


Taking regular exercise is one of the best things you can do for your health. Among its many benefits, exercise is vital for maintaining a healthy immune system. As a guide, the NHS recommends that, each week, adults should do 150 minutes of moderate intensity exercise like brisk walking, dancing or riding a bike.

Unhealthy habits

Smoking and drinking too much alcohol are two habits that increase your risk of life-threatening conditions like cancer and stroke. But did you know they’re also bad for your immune system? If you’re looking to get healthier, quitting smoking and cutting back on alcohol is a great place to start.

Stop smoking tool

Good hygiene

It may seem like an obvious point, but one of the best ways to avoid getting sick is to make sure you’re practising good hygiene – particularly around other people who are ill. A good start is to get into the habit of washing your hands with soap and warm water regularly – read our guide for more tips.