Is Vitamin D Good For The Immune System?

  • 1st Revision: Maura Mary Joseph

Immune system and vitamin D

Immune system is the army of our body that protects us from invaders like pathogens/bacteria and different diseases and keeps us healthy. Vitamin D plays a major role in enhancing and regulating the immune system. In our body, there are receptors of Vitamin D present on immune cells, when Vitamin D binds to the receptors on the immune cells, it stimulates the production of peptides from immune cells which are responsible for killing bacteria and viruses. In that way, Vitamin D  regulates the activity of immune cells and helps in fighting off the infection and  strengthening the immunity of our body.1 Such peptides which possess antiviral and antimicrobial activity are called as defensins and these peptides are part of the immune system.2 Not only Vitamin D help in the activation of immune cells against the infection but also plays a vital role in controlling inflammation by suppressing immune responses when an infection is severe.3 Controlling inflammation in case of severe infection is necessary as inflammation can cause damage to other organs of the body, and it can lead to lung injury, malfunctioning of the kidney, and respiratory distress.4

Food sources of vitamin D

Vitamin D is present in a rich amount in animal foods, fish, egg yolk, and milk. Other food sources which contain significant amounts of Vitamin D are meat, eel, herring, egg and egg yolk, salmon, pike-perch, tuna, cod, butter, and wild mushrooms are good sources of Vitamin D.5

Table 1: Amount of Vitamin D in Major Food sources6

Food SourceAmount of Vitamin D
Fortified milk 2.5 per cup 
Fish5–15 per 100 g
Fortified juice 2.5 per cup
Fortified cereals 1–1.5 per cup 

Benefits of vitamin D to the immune system

Vitamin D plays a vital role in enhancing immunity against respiratory infections. It has been proved by researchers through experimentation that supplementation of Vitamin D significantly decreased the risk of respiratory infections.7 If the right dose of Vitamin D is taken, it can reduce the risk of respiratory infection up to 7%.8 Not only against respiratory infections, vitamin D also boosts immunity against colds and flu. Usually, flu and cold season peaks in winter, because deficiency of Vitamin D is more prevalent in winter.9

Low levels of vitamin D increase the risk of a compromised immune system which can lead to rheumatoid arthritis, diabetes, multiple sclerosis, and inflammatory bowel disease.10 It has been evidenced by scientific studies that these conditions are more frequently caused by the low levels of Vitamin D in the body and can even become worse. Even supplements of Vitamin D help in recovering from coronavirus as it strengthens the immune system. All of these studies emphasize on how much vitamin D is important and beneficial for boosting the immune system and protecting from different diseases.11

There are receptors in our body that secrete vitamins upon exposure to sunlight and the production of vitamin D stimulates the bacteria-killing cells of the immune system. Vitamin D promotes immune responses and eliminates pathogens to prevent tissue damage due to excessive inflammation of bacterial infection. Deficiency of vitamin D makes the immune system susceptible to bacterial or viral infection. With the advent of effective antibiotics, vitamin D was used for the treatment of bacterial and viral infections. Especially for tuberculosis, in the past, patients with tuberculosis were sent to the sanatoriums where they were given treatment including exposure to the sunlight by thinking that exposure to sunlight produces vitamin D that directly kills the tuberculosis bacteria. Moreover, vitamin D-rich food has also been used as a treatment for tuberculosis to strengthen the immune system against infection. Thus, vitamin D is beneficial for strengthening the immune system as it shows antimicrobial and anti-inflammatory properties as well.10

Symptoms of vitamin D deficiency

Deficiency of vitamin D can manifest as sweakness of bones due to loss of calcium, bone deformation,  and worsen osteoporosis, leading to a high risk of skeletal fractures.12 Other manifestations are symmetric low back pain, muscle weakness, and aches leading to increased risk of falls, bone pain, low back pain usually in women, throbbing, and weakened immune system.13

Risk factors for vitamin D deficiency

  • More than 65 years old individuals are susceptible to vitamin D deficiency13
  • Insufficient exposure to sunlight13
  • Use of medication that alters the metabolism of vitamin D like glucocorticoids, and anticonvulsants13
  • Obesity can be a risk factor for vitamin D deficiency in our body13

Risk of taking too much vitamin D 

Excess of everything is bad so taking too much of Vitamin D can cause problems. Excessive vitamin D is toxic, signs of vitamin D toxicity are nausea, vomiting, kidney stones, abdominal pain, pancreatitis, headache, loss of appetite, excessive urination and thirst, vascular calcinosis, and metallic taste. According to the National Academy of Sciences, the risk of vitamin D toxicity is less if supplementation levels of  vitamin D are up to 2,000 IU (international unit) per day. The toxicity of vitamin D can be treated by stopping the consumption of vitamin D supplements.13,14


Vitamin D is the booster and protector of our immune system. It strengthens the immune system to maintain your health. Sunlight is the natural source of Vitamin D, exposure to the sunlight can trigger vitamin D production in our body as receptors of vitamin D are present in our body. It is a rational fact that a low amount of vitamin D makes the immune system compromised and you fall prey to many infectious diseases. So, it’s important to add vitamin D to your diet. The best sources of vitamin D are fish, milk, egg yolk, mushrooms, and meat. In the presence of enough vitamin D in the body, the immune system works more effectively as vitamin D activates many germs/pathogen-killing cells of the immune system which helps in fighting off the infection. Lack of Vitamin D  weakens the immune system, so proper intake of vitamin D is important for strengthening the immune system.


  1. Bryson KJ, Nash AA, Norval M. Does vitamin D protect against respiratory viral infections?. Epidemiology & Infection. 2014 Sep;142(9):1789-801.
  2. Gwyer Findlay E, Currie SM, Davidson DJ. Cationic host defence peptides: potential as antiviral therapeutics. BioDrugs. 2013 Oct;27(5):479-93.
  3. Grant, W. B., Lahore, H., McDonnell, S. L., Baggerly, C. A., French, C. B., Aliano, J. L., & Bhattoa, H. P. (2020). Evidence that vitamin D supplementation could reduce risk of influenza and COVID-19 infections and deaths. Nutrients, 12(4), 988.
  4. Parlak E, Ertürk A, Çağ Y, Sebin E, Gümüşdere M. The effect of inflammatory cytokines and the level of vitamin D on prognosis in Crimean-Congo hemorrhagic fever. International Journal of Clinical and Experimental Medicine. 2015;8(10):18302.
  5. Lamberg-Allardt C. Vitamin D in foods and as supplements. Progress in biophysics and molecular biology. 2006 Sep 1;92(1):33-8.
  6. Weaver CM, Fleet JC. Vitamin D requirements: current and future. The American journal of clinical nutrition. 2004 Dec 1;80(6):1735S-9S.
  7. Martineau AR, Jolliffe DA, Hooper RL, Greenberg L, Aloia JF, Bergman P, Dubnov-Raz G, Esposito S, Ganmaa D, Ginde AA, Goodall EC. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. bmj. 2017 Feb 15;356.
  8. Berry DJ, Hesketh K, Power C, Hyppönen E. Vitamin D status has a linear association with seasonal infections and lung function in British adults. British Journal of Nutrition. 2011 Nov;106(9):1433-40.
  9. Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Ensayo aleatorio de la suplementación con vitamina D para prevenir la influenza estacional A en escolares. J. Clin. Nutr. 2010;91:1255-60.
  10. Aranow C. Vitamin D and the immune system. Journal of investigative medicine. 2011 Aug 1;59(6):881-6.
  11. Maghbooli Z, Sahraian MA, Ebrahimi M, Pazoki M, Kafan S, Tabriz HM, Hadadi A, Montazeri M, Nasiri M, Shirvani A, Holick MF. Vitamin D sufficiency, a serum 25-hydroxyvitamin D at least 30 ng/mL reduced risk for adverse clinical outcomes in patients with COVID-19 infection. PloS one. 2020 Sep 25;15(9):e0239799.
  12. Weaver CM, Fleet JC. Vitamin D requirements: current and future. The American journal of clinical nutrition. 2004 Dec 1;80(6):1735S-9S.
  13. Bordelon P, Ghetu MV, Langan RC. Recognition and management of vitamin D deficiency. American family physician. 2009 Oct 15;80(8):841-6.
  14. Kelly Burch [Internet]. Why high dose vitamin D supplements could cause side effects [Published 2021 October 8]. Available from
This content is purely informational and isn’t medical guidance. It shouldn’t replace professional medical counsel. Always consult your physician regarding treatment risks and benefits. See our editorial standards for more details.

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Bushra Razzaq

Bachelors of Biotechnology, Capital University of Science and Technology, Pakistan

Bushra is a Biotechnologist with great passion of doing research in Health Sciences. She wants to unfold the mystery of genetic diseases and explore the treatment of genetic diseases in medicinal plants. She has done research on treating cancer using medicinal plant.
She is a fresh graduate, with great experience of writing articles for health sciences. She is looking for writing more about health and life sciences to deliver the knowledge to the general public. presents all health information in line with our terms and conditions. It is essential to understand that the medical information available on our platform is not intended to substitute the relationship between a patient and their physician or doctor, as well as any medical guidance they offer. Always consult with a healthcare professional before making any decisions based on the information found on our website.
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