The Importance of Diet for Immune Function

The immune system is one of the most complex bodily systems, made up of an intricate network of cells, molecules, tissues, and organs all working together to protect the body and keep us functioning at our best.¹ To function optimally, our immune system must be able to distinguish the self from the non-self.¹ This includes being able to identify between non-self-molecules which are harmful, like invading viruses and bacteria, and harmless non-self-molecules like those from the food we eat.²  

The Role of a Wholefood Diet

Nutrition plays an essential role in the regulation of immunological responses and the function of immune cells.² When supporting the immune system through diet, we want to include a wide variety of fruits and vegetables, wholegrains, nuts and seeds, and protein from meat, seafood, and legumes.

Ensuring you are consuming a wide variety of wholefoods provides your body and immune system with a broad variety of essential vitamins, minerals, healthy fats, and proteins which are required for all cells in our body to function at their best.²

Diets that have a large amount of processed, packaged, and refined sugary foods tend to be nutrient deficient. They are generally associated with increased inflammation in the body, disturbances in the balance between good and bad bacteria within the gut and an imbalanced immune system.¹ Following highly restrictive diets for long periods of time can also lead to nutrient deficiencies.³

Maintaining a Healthy Diet Seasonally

Generally during the winter months, we experience an increased number of infections from colds and flus, mainly from spending more time indoors and in closer proximity to other people.⁴ Once we have become infected with a virus or bacterial pathogen, our immune system becomes activated and this further increases the demand for energy and nutrients, especially when we experience a fever.¹

Having optimal nutritional stores during an infection allows for immune cells to work effectively and rapidly.¹ This can be supported by maintaining a whole food diet all year round and choosing fresh foods that are locally available and in season.

Specific Nutrients for Healthy Immune Function

Certain vitamins and minerals that are particularly important to support the development, growth and function of immune cells include:

Vitamin C: helps to support increases in blood levels of antibodies, which are needed to fight off infections, and helps to differentiate white blood cells, which helps the body determine what kind of immune protection is needed.⁵ It is also a potent antioxidant.⁵

Food sources include green leafy vegetables, broccoli, capsicums, citrus fruits, tomatoes, berries, and kiwi fruit.

Vitamin D: helps to support the functioning of the innate immune system, which is our first line of defence.⁶ It also has been shown to have antibacterial activity within specific immune cells, protecting against invading bacteria.⁶

Food sources include fatty fish such as salmon, sardines and mackerel, sundried mushrooms and cod liver oil.

Vitamin A: is a potent antioxidant and supports the immune system by helping antibodies respond to invading pathogens more effectively.⁷

Food sources include beef liver, sweet potato, carrot, capsicum, pumpkin, spinach, mangoes and apricots.

Zinc: is required for supporting immune responses, especially immune cell development and communication.⁸ Zinc plays an important role in regulating the necessary inflammatory response of the immune system when we become infected and acts as an antioxidant.⁸ Research has shown that a mild deficiency in zinc has been associated with an imbalance in the functioning of both the adaptive and innate immune response and a greater risk of infections.⁸

Food sources include seafood (especially oysters), beef, pork, chicken, legumes, seeds, nuts, eggs and whole grains.

Selenium: is a potent antioxidant and can help reduce inflammation specifically within the respiratory tract.⁹ A diet that is deficient in selenium may result in impaired immune responses and an increased susceptibility to infections.⁹

 Food sources include seafood, organ meats and nuts such as Brazil nuts.

The Importance of Hydration

Research has shown that our immune cells function better when we are adequately hydrated.¹⁰ The mucous membranes in our mouth need plenty of water to produce salivary immunoglobulin A, which is one of the first lines of defence against invading bacteria and viruses.¹⁰  Dehydration has been linked with poorer functioning of immune cells, specifically neutrophils, a type of white blood cell that helps to fight infection.¹¹ Being properly hydrated also helps to deliver nutrients and oxygen to your cells.¹²

Aim to keep well hydrated, especially in the winter months when you might not feel as thirsty. Herbal teas and bone broths can be incorporated to help maintain optimal hydration. How much water you should be drinking can be variable depending on exercise levels, weight, if you’re pregnant or breastfeeding, however aiming for at least 2 – 2.5 litres a day is a good start.

References

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10. Fortes MB, Diment BC, Di Felice U, Walsh NP. Dehydration decreases saliva antimicrobial proteins important for mucosal immunity. Applied Physiology, Nutrition, and Metabolism. 2012 Oct;37(5):850-9.
11. Chishaki T, Umeda T, Takahashi I, Matsuzaka M, Iwane K, Matsumoto H, Ishibashi G, Ueno Y, Kashiwa N, Nakaji S. Effects of dehydration on immune functions after a judo practice session. Luminescence. 2013 Mar;28(2):114-20.
12. Better Health Channel. Water – a vital nutrient [Internet]. Melbourne: Department of Health, State Government of Victoria; 2021 November 9. Available from  https://www.betterhealth.vic.gov.au/health/healthyliving/water-a-vital-nutrient