What is our immune system?

Your immune system is your body’s defence against illness and infection. The immune system plays a diverse role in protecting you from catching a common cold, all the way to protecting you from certain cancers!

It recognises every cell in your body as your own, so if anything, unfamiliar enters your body like bacteria and viruses, it recruits an army of immune cells to fight it off.

Sometimes, this goes wrong, such as in the case of hay fever, when the body mounts an immune response to a harmless substance such as pollen, and in more debilitating conditions such as autoimmune disease, when your body can react against your own tissues.

How can we maintain a healthy immune system? I hear you ask!

Your diet may play a role in the optimal functioning of your immune system. Studies have shown that vitamins such as vitamin A, C and D all contribute to immune cell functioning.[1],[2]

  • Studies show 100mg vitamin C per day is required to prevent infections[3] and this level can be obtained from foods like citrus fruits, peppers, broccoli and tomatoes.
  • Vitamin D is mainly obtained from sunlight as many as 1 in 5 people in the UK are deficient in Vitamin D over the winter months (recommended amount is 600-800IU per day, depending on age and sun exposure).[4],[5] Food sources of vitamin D include oily fish such as salmon or tuna, milk and fortified cereal. You can also get vitamin D from cod-liver oil, or vitamin D supplements.

But diet is just one part of a very complex picture. Your immune system may be influenced by your lifestyle and health as a whole, so this means getting enough sleep, regular exercise and managing stress.

Author: Dr Frankie Jackson-Spence

[1] Mora, J. (2010) 'Vitamin effects on the immune system: vitamins A and D take centre stage', Nature Review Immunology , 8(9), pp. 685-698 [Online]. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2906676/

[2] Carr, A. (2017) 'Vitamin C and Immune Function', Nutrients, 9(11), pp. 1211 [Online]. Available at: (Accessed: https://www.ncbi.nlm.nih.gov/pubmed/29099763)

[3] Carr, A. (2017) 'Vitamin C and Immune Function', Nutrients, 9(11), pp. 1211 [Online]. Available at: (Accessed: https://www.ncbi.nlm.nih.gov/pubmed/29099763)

[4] National Institutes of Health (2019) Vitamin D, Available at: https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/

[5] Office of National Statistics (2014) NDNS: results from Years 1 to 4 (combined), Available at: https://www.gov.uk/government/statistics/national-diet-and-nutrition-survey-results-from-years-1-to-4-combined-of-the-rolling-programme-for-2008-and-2009-to-2011-and-2012