The importance of nutrition to optimise our immune system

The importance of nutrition to optimise our immune system

The nutrients we consume really are the basis for a good immune system. Our immune system is complex and requires a variety of different components to help it function properly.

We are constantly being exposed to microbes each and every day, some are which are beneficial, while others have the potential to be harmful. Our immune system helps to protect us against the not so good microbes, including certain diseases. It is able to recognise foreign parasites, viruses and bacteria and take action towards them.

As humans, we have two different types of immunity: innate and adaptive immunity.

Our innate immunity is best known as our 'first-line of defence' and is achieved through different types of protective barriers. These can include our skin that helps to keep pathogens out of our body, mucus which traps pathogens, stomach acid that helps destroy these pathogens, anti-bacterial compounds found in tears and sweat and the cells of our immune system that attack foreign cells that enter in our body.

Adaptive immunity is referred to as the body’s ability to learn or recognise a pathogen after it has been exposed to one. Adaptive immunity is activated when the innate immune response is unable to control an infection. It is regulated by organs and cells in our body like the spleen, thymus, bone marrow and lymph nodes.

Well balanced nutrition is necessary for the optimal functioning of all cells of the body, including the innate and adaptive immune system. Whilst there is no single diet which is superior to all others, there are certain dietary patterns that may promote less inflammation and contribute to an intake of optimal nutrients required for the growth and function of our immune cells. It is important to note that diets that include high amounts of highly processed foods, or which have a higher saturated fat and sugar content are more likely to promote unhealthy levels of inflammation and disrupt an effective immune response.

Throughout each step of the body's immune response, the presence of certain micronutrients like vitamins C, D, B vitamins, zinc, and antioxidants are vital. Poor nutritional status and/or limited access to healthy and fresh foods can contribute to nutritional deficiencies, which may predispose us to certain infections due to the suboptimal effects of a weakened immune system. In some cases, our normal dietary intake and practices may not be sufficient to achieve optimal nutritional intake of certain nutrients, and supplementation with these nutrients may therefore be important for certain populations which are deficient in dietary intake of adequate amounts of nutrients like zinc.

So let us take a look at each individual nutrient and the affect these might have on the immune system.

Vitamin C

Vitamin C plays an important role in several aspects of immunity by helping to reduce the duration and severity of infection. Vitamin C is required for collagen biosynthesis and for maintaining epithelial integrity, meaning it helps to keep your bones and connective tissues healthy, and allows iron to be absorbed more effectively. Sources of vitamin C include blackcurrants, citrus fruits, berries, kiwifruit, tomatoes, broccoli, sprouts and capsicum.

Vitamin D

Vitamin D is required by the body to absorb calcium and to help maintain bone and muscle health. Vitamin D receptors have been found on most immune cells in the body and have been found to have immunomodulatory properties. As most people know, we are able to get vitamin D from the sun, however most people, especially those during winter, do not receive sufficient amounts of sunlight to reach the recommended levels.

More than 70% of Australians suffer from vitamin D insufficiency (serum vit D <75nmol/L), and almost 1 in 4 Australians are vitamin D deficient (serum Vit D <50nmol/L). Very few foods contain a great deal of vitamin D, however the best sources are found in fatty fish, like salmon, mackerel, herring and eggs. Some foods that have been fortified with vitamin D include milk, soy drinks, breads and cereals. Supplementation with vitamin D has been found to help reduce the risk of developing respiratory tract infections.

B group Vitamins

(Vitamin B2 - Riboflavin, Vitamin B6 - Pyridoxine, Vitamin B12 - Cobalamin, Folate) have an array of functions in the body. In regards to immunity, they are involved in intestinal immune regulation which contributes to gut barrier function.

B6, B12 and folate support the activity of natural killer cells and cytotoxic T- Lymphocytes which may be important in antiviral defence. B vitamins are available in a variety of foods including vegetables, legumes, beans, fruit, whole grains, lean meats, poultry, eggs, tofu, nuts and seeds, dairy products and their dairy-free alternatives.


Zinc is an essential micronutrient which plays a role in the regulation of immune function. A substantial amount of scientific literature has documented the beneficial role of zinc in fighting respiratory tract infections such as common cold and flu. Zinc is found in a variety of foods, including meat, fish, poultry, cereals and dairy foods.

Protein helps the body to absorb zinc, so for those people who reduce their protein intake or are on long-term restrictive diets may find themselves at a higher risk of becoming deficient. Deficiency can also occur in those with nutrient absorption issues (e.g. coeliac disease). Supplementation for these groups under the guidance of a health professional is recommended.


Antioxidants are substances that are found in food that are known to help neutralise free radicals in the body. Free radicals can be both beneficial and detrimental to our body. They can be used by our body's immune system to help fight viruses and bacteria, but they can also cause damage to cells and can contribute to health problems. For optimal functioning of the immune system and the maintenance of homeostasis, it is important to maintain a balance of free radicals and antioxidants.

The most common antioxidants are vitamins A, C, E, beta-carotene, lutein, lycopene, selenium, coenzyme Q10, N-acetyl-cysteine and the newly popular Quercetin (which we love!). Evidence suggests that suboptimal levels of antioxidants are associated with impaired immune responses and an increased susceptibility to infections. Supplementation of antioxidants may help to improve the immune response by supporting both our innate and adaptive immunity, whilst being able to protect the immune response to those exposed to high levels of oxidative (free radical) stress.

Certain things we can do to optimise our antioxidant intake through diet choices include:

  • Eating whole foods: This means foods you can make from scratch from foods that are grown from the earth. Foods that don't require a label to read in order to understand what’s contained within.
  • Ensuring daily adequate protein consumption: this doesn’t mean taking protein in excess, nor does it mean you have to eat animal proteins either. If you do choose to consume animal proteins, try to opt for grass-fed where possible and include a variety from other sources throughout your day. The diversity will not only help feed good bacteria in our gut but in turn it will help support the immune system.
  • Fat isn’t our foe! (as long as it’s the right kind of fat!): Every cell in our body is surrounded by a membrane made up of fats, the composition of which is determined by our diet so it’s important to incorporate healthy fat sources from nuts, seeds, avocados, olive oil, eggs from pasture raised chickens, and wild caught sustainable fish.
  • Fill at least half your plate with fresh produce: vegetables provide essential nutrients that help ensure our immune system runs effectively.

Diets that are high in refined sugars, saturated fats and processed foods and low in fresh fruit, vegetables, legumes and whole-grains can promote unhealthy alterations in the composition of intestinal microorganisms which can result in chronic inflammation and suppressed immunity.

So what are the takeaway points here?

  1. Eat a balanced diet with a variety of whole-foods, fruits, vegetables, lean proteins, whole grains and plenty of water.
  2. Where a balanced diet is not accessible, or deficiencies are at play, a multivitamin or nutraceutical supplement containing at least the RDI of the specific nutrients may be used.
  3. Limit alcohol and cigarette consumption.
  4. Engage in regular moderate exercise daily.
  5. Aim for 7-9 hours of sleep every night. Trying as best as we can keeping to a similar schedule to ensure balanced circadian rhythms are maintained and a deeper and restful sleep is attained.
  6. Manage stress. This is easier said than done, but if some helpful strategies are put in place that work for your lifestyle and routine, this can be extremely beneficial when feelings of stress arise. This might involve regular exercise, meditation, a hobby like painting or playing the guitar, talking to a trusted friend of family member or even practicing conscious breathing techniques throughout the day.
  7. Practice safe and clean hygiene practices like regular hand washing to avoid the spread of germs.


  1. Childs, C. E., Calder, P. C., & Miles, E. A. (2019). Diet and Immune Function. Nutrients, 11(8), 1933.
  2. Harvard T.H.Chan School of Public Health, Nutrition and Immunity:
  3. Maggini, S., Pierre, A., & Calder, P. C. (2018). Immune Function and Micronutrient Requirements Change over the Life Course. Nutrients, 10(10), 1531.