The importance of Vitamin D3 in immune function


Vitamin D3 has become very well known over the past years for the role it plays in calcium absorption and bone homeostasis, however Vitamin D3 is so much more than just a regulator of bone health. Along with bone health Vitamin D3 is important for helping prevent cancer, reducing the risks of low birth weight and post natal depression, elevating mood, and is involved in neuromuscular and immune function.

In recent years it has become more apparent that Vitamin D3 deficiency can increase your susceptibility to infections and may even be implicated in autoimmune disease. This fat-soluble vitamin plays a big role in how your immune system functions through its activation of specific immune cells in response to any serious infectious attack on the body.

Vitamin D is photosynthesised in the epidermis and dermis of the skin by the UVB rays from the sun. The increased use of sunscreen in Australia over the past couple of decades due to the increase in skin cancer, has had a substantial effect on Vitamin D levels. The sunscreen effectively blocks the UVB rays responsible for the conversion of Vitamin D. Other factors that reduce the conversion of Vitamin D include the time of day, season and latitude, darker skin pigmentation (melanin), sedentary lifestyle with little outdoor activities, birth of a child to a mother that was Vitamin D deficient.

Dietary sources of Vitamin D include cod liver oil, eggs and fatty fish such as salmon, herring and mackerel or Vitamin D can be taken as a dietary supplement. Many countries also fortify their food with extra Vitamin D to reduce the risks of deficiency. 

Due to Vitamin D being a fat soluble vitamin, it is important to take into account intestinal absorption. If there is an issue with fat malabsorption, you may not be absorbing your fat soluble vitamins and therefore may need to address any digestive dysfunction first. Inflammation and food intolerances are often the culprits.

For help identifying any underlying digestive dysfunction it is recommended to speak to a qualified Naturopath or Nutritionist so you can get the correct advice and be on your way to a stronger and healthier immune system.


1. Braun L, Cohen M. Herbs and natural supplements: an evidence-based guide, 3rd ed., 2010.

2. Daly RM Gagnon C, Lu ZX, et al. Prevalence of vitamin D deficiency and its determinants in Australian adults age 25 years and older: A national, population-based study. Clin Endocrinol 2012;77(1):26-35.

3. Shils ME, Shike M, Ross AC, Caballero B & Cousins RJ. Modern Nutrition: in health and disease, 10th ed., Lippincott Williams & Wilkins, 2006.


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