Written by Aisling Moran BSc (Hons)
19th Jul 2022 • 10 minute read

Your immune system defends your body against harmful things, like viruses and bacteria, protecting you from infections and diseases. Despite claims, there’s no magic pill to boost your immune system. In fact, if something were to boost your immune system, it could be quite dangerous. But, there are lots of lifestyle factors that can affect how it functions.

Diet and your immune system

A healthy balanced diet is really important when it comes to supporting the functioning of your immune system and long-term health. There are a number of nutrients that are particularly important.

Vitamin C

Vitamin C is a powerful antioxidant (protects your cells against damage) that you get from food. It’s been shown to support your immune system in a number of ways. Firstly, it supports your epithelial barrier function — this is a barrier that regulates the nutrients you absorb and help prevent harmful bacteria from entering your body.

Vitamin C has also been shown to build up in immune cells called phagocytes, possibly enhancing their function. These are cells that ingest and destroy something that’s harmful, like bacteria and viruses. 

Also, vitamin C deficiency has been linked to a weakened immune system, increasing your susceptibility to infections. 

Should you take a vitamin C supplement?

Vitamin C deficiency is uncommon in the UK, and you should be able to get enough from a balanced and varied diet. The best sources of vitamin C are:

  • peppers
  • oranges
  • kiwis
  • broccoli 
  • brussels sprouts

But you might have heard of people taking high doses of vitamin C to ward off colds. Unfortunately, high-quality research doesn’t show that vitamin C supplementation can protect you from developing a cold. But there does seem to be some exceptions. It looks like vitamin C supplementation can decrease the incidence of colds for certain groups of people — like people training for a marathon who are under a lot of physical stress.

In terms of how severe a cold is or how long it lasts, some evidence suggests that taking a regular vitamin C supplement might reduce the severity and duration of a cold

Vitamin A

Vitamin A is sometimes called an anti-inflammation vitamin because of how it supports your immune function. Vitamin A strengthens your immune barrier, as it helps form the protective lining around your organs. It’s also needed to form phagocytes — immune cells that engulf and destroy harmful materials. And similar to vitamin C, vitamin A deficiency is associated with a weakened immune system (increasing your risk of infection).

There are two forms of vitamin A in your diet:

  • retinol —  found in dairy, fish, and meat (particularly liver) 
  • carotenoids — the most important type of carotenoid in your diet is beta-carotene which is found in spinach, carrots, sweet potatoes, red peppers, and mango.

Should you take a vitamin A supplement?

A varied and balanced diet should provide you with all the vitamin A you need. Too much vitamin A can be harmful. For example, it can increase your risk of osteoporosis if you have more than 1.5 mg per day for years. To make sure you don’t have too much:

  • don’t eat liver or liver products, like pâté, more than once a week
  • don’t take any vitamin A supplements if you eat liver once a week
  • if you do take a vitamin A supplement, don’t take more than 1.5 mg a day

If you’re pregnant, it’s important to avoid having large amounts of vitamin A — this can be harmful to your baby. Also, avoid taking a supplement containing vitamin A or eating liver and liver products.

Vitamin E

Like vitamin C, vitamin E is a powerful antioxidant that helps your body fight off infection. The best sources of vitamin E are plant oils, like olive oil, nuts, seeds, and wheat germ.

Should you take a vitamin E supplement?

Taking a vitamin E supplement only seems to be beneficial if you have a deficiency, which is rare. Vitamin E deficiencies are usually only an issue if you have trouble absorbing fat (like with Crohn’s disease or cystic fibrosis) or if you follow a very low-fat diet. This is because vitamin E is fat-soluble — meaning your body needs fat to absorb it.

Vitamin D

While the mechanisms aren’t fully understood, vitamin D plays an important role in supporting your immune system. In fact, a reported sign of vitamin D deficiency is getting sick often. Some evidence even suggests vitamin D supplements can help reduce your risk of developing a cold or flu, but more research is needed. In addition to this, vitamin D has also been linked to the prevention and protection against autoimmune diseases. 

Should you take a vitamin D supplement?

Aside from these possible effects, maintaining good vitamin D levels is important for a wide range of reasons — it’s needed for healthy bones, teeth, and muscles. And with 40% of the UK estimated to be vitamin D deficient during winter, taking a supplement is often recommended. This is because sunlight is your main source of vitamin D, and it’s very difficult to get enough from food.

During autumn and winter, Public Health England advises that everyone should consider taking a 10 mcg daily vitamin D supplement from October to March. And if you’re more at-risk, they recommend taking them year-round. The recommended doses for at-risk groups include:

  • 8.5-10 mcg daily for breastfed babies from birth to 1 year
  • 10 mcg daily for children aged 1-4 years
  • 10 mcg daily for at-risk adults — for example, if you’re elderly or have darker skin

Vitamin B6

Evidence suggests that vitamin B6 plays an important role in your immune function. A deficiency has been linked to a decreased production of antibodies — protective proteins that help your body fight infection. It might also affect your production of white blood cells.

Vitamin B6 is naturally found in many foods, including poultry, fish, eggs, whole grains, potatoes, and vegetables.

Should you take a vitamin B6 supplement?

You should be able to get all the vitamin B6 you need from a varied and balanced diet. If you do take a supplement, it’s important not to have more than 10 mg a day unless advised by a health professional. Taking more than 200 mg a day for a long time can lead to a loss of feeling in the arms and legs — called peripheral neuropathy. This will usually improve once you stop taking the supplement.


Zinc is a mineral you get from your diet, but, you might also notice that it’s often found in cold lozenges and remedies. Zinc plays a key role in your immune function, and a deficiency has been shown to negatively affect your immune cells.

Good sources of zinc include shellfish, red meat, dairy, nuts, seeds, lentils, chickpeas, and whole grains. 

Should you take a zinc supplement?

While a balanced and varied diet should provide you with everything you need, some groups of people might need to consider a supplement. For example, if you follow a vegan diet — check you’re getting enough using the free dietary self-assessment app from The Vegan Society, VNutrition.

Some research indicates that taking zinc within 24 hours of the start of cold symptoms might reduce the duration and severity of symptoms. But it’s unclear what dose and form are the best to take. Taking too high a dose can also have possible side effects — like trouble absorbing copper, nausea, loss of appetite, and temporary taste issues.

Other foods and supplements

There are a number of supplements that might help support your immune function. It’s also a good idea to talk to your pharmacist or a qualified health professional before starting a supplement. 

Supplements that might support your immune function include:

  • echinacea — studies have shown that this herb might help defend against the common cold (but a lot more research is needed)
  • black elderberry extracts — a medicinal plant that has been shown to reduce the duration and severity of the flu (but research is based on only a few studies with a small number of people involved)
  • aged garlic extract (AGE) — some research suggests that AGE can enhance your immune cell function and might help reduce the severity of colds and flu

Find out more about how to choose supplements.


Probiotics are types of live bacteria and yeast that are taken as a supplement to support a healthy gut. It’s estimated that 70% of your immune function sits in your gut. So, a healthy gut might improve your immune function. Again, this evidence is emerging, so no firm conclusion can be drawn yet.

But it’s well-supported that eating a diet high in fibre is really important for a healthy gut. 

Current guidelines suggest aiming for 30g of fibre a day. Fibre-rich foods include whole grains, fruits, veggies, nuts, seeds, and pulses. Plus, some types of whole grains, like oats, are prebiotics — promoting the growth and activity of ‘good’ bacteria in your gut. So eating a lot of whole grains can really help to improve your gut health and digestion.

Alcohol and your immune system

Try to avoid binge drinking as it might negatively affect your immune function. For example, it might slow down how quickly you recover from an illness or increase your risk of developing an infection. Binge drinking is classed as drinking more than:

  • 8 units of alcohol in a single session for males — 5 small glasses of wine or 5 bottles of beer
  • 6 units of alcohol in a single session for females — 2 large glasses of wine or 2 pints of beer

Find out more about how alcohol affects your health.

Sleep and your immune system

When you sleep, your body produces and releases cytokines — proteins that target infection and inflammation. Sleep is also thought to improve the functioning of your T cells — a really important type of immune cells. So a lack of sleep, or not enough quality sleep, can make you more susceptible to sickness. It might also affect how quickly you recover from sickness. 

For adults, the optimal amount of sleep is 7-8 hours of good-quality sleep a night. If you don’t manage to sleep enough, two naps (no longer than 30 minutes each) can help offset the negative effects of sleep loss. Of course, naps aren’t always a feasible option for everyone. Try to find a sleep routine that works for you.

Stress and your immune system

Your emotional wellbeing can have a big impact on your physical health. In fact, psychoneuroimmunology is the study of the interactions between your central nervous system (CNS) and your immune system. And research shows that chronic stress can weaken your immune system.  

There are lots of things that you can do to lower your stress levels and even change how you perceive and respond to stress, including:

  • mindfulness
  • deep breathing
  • getting enough sleep
  • exercise
  • not drinking too much

Exercise and your immune system

Regular exercise is important for the functioning of your immune system. There are a lot of theories about how exercise might support your immune system, but the mechanisms aren’t fully understood. One theory is that exercise can help your immune cells travel more quickly around your body as it improves your circulation. Or it could be that the brief increase in your body temperature might help you fight infections better. It’s likely a combination of complex reasons.

Keep in mind that prolonged (more than 90 minutes) moderate-high exercise, particularly done without eating, might suppress your immune function in the short term. So it’s important to give your body time to recover between workouts. But this tends to only be an issue for athletes during periods of prolonged heavy training. 

Smoking and your immune system

Smoking increases your susceptibility to infection, like colds and flu, and is linked to more severe and longer-lasting illnesses. It might also lower the levels of protective antioxidants, like vitamin C, in your blood.

Hygiene and your immune system

Washing your hands regularly with soap and water for 20 seconds can help protect you from developing an infection if you’ve been exposed. If you can’t wash your hands, and alcohol gel with an alcohol level of at least 60% is the next best thing.