Did you know that without vitamin D you can consume as much calcium as you like but it will just get lost in your urine?


Vitamin D's main job is to help increase calcium absorption which therefore helps us to build bone. 

This vitamin is also involved in the body's immune system, brain and nervous system, pancreas, skin, muscles, cartilage and reproductive organs so it really is a super important vitamin to ensure you have adequate levels of. 


There are two forms of vitamin D in the diet:

  • Vitamin D2 (ergocalciferol) found in some mushrooms.
  • Vitamin D3 (cholecalciferol) found in oily fish such as salmon, herring and sardines as well as fish liver oil and egg yolks. It can also be found in veal, beef and liver, as well as fortified milks, margarine and butter.

D3 is the more potent of the two types and raises blood levels of vitamin D almost twice as much as D2.

Large amounts of Vitamin D3 can also be made in your body when your skin is exposed to ultra-violet rays from sunlight. 

For most people, exposing hands, face and arms on a clear summer day for 15 minutes on either side of the peak UV periods on a daily basis should be sufficient to maintain vitamin D levels. In winter 2-3 hours of sunlight over the week is necessary. 

And because it's a fat soluble vitamin, it means that any excess vitamin D can then be stored in your body fat for later use which is helpful if you live in an area of the world that lacks sun exposure in the winter months.


Every cell in your body has a receptor for vitamin D. When ultra-violet rays from the sun penetrate the skin, it converts pre-vitamin D3 (a precursor made in the liver from cholesterol) into its active form, vitamin D3

Vitamin D’s main role is to help build bone by:

  • Increasing the absorption of calcium from foods in the gut
  • Enhances the kidneys ability to retain calcium
  • Mobilises the body’s ability to draw calcium from the bones, a process called bone remodelling


A lack of vitamin D can result in the following disorders:

  • Osteopenia - where people have low bone mass 
  • Osteoporosis - when there is not only low bone density, but the bones become porous and brittle
  • Osteoarthritis - the degeneration of articular cartilage such as the bony ends touching and causing friction with each other
  • Osteomalacia in adults or rickets in children where the bones become soft or rubbery and as a result, deformed in the form of bowed legs.


Just go outside and that will do the trick you say? Well it's not quite that simple. There are several factors that will affect absorption:

  • Living mostly indoors
  • Simply standing next to a sunlit window will not help. Windows actually block certain rays and you need the full spectrum of light to efficiently synthesise vitamin D
  • Wearing clothing that conceals the skin such as a long sleeved shirt and pants will give you no benefit despite being outdoors, apart from the fresh air. Your face, arms and legs need to be exposed to the sun 
  • Wearing sunscreens with high sun protection factors inhibit vitamin D production. It's best to apply this after you've had at least 15mins of sun exposure first
  • Heavy clouds or pollution blocking the ultra-violet rays of the sun. You need direct sunlight so your skin is exposed to the full spectrum of light
  • People with darker skin require longer sunlight exposure due to the pigment of the skin providing protection to sun damage which in turn reduces vitamin D production
  • Geographic location and seasonality affecting sun exposure. If you live far north or south of the equator, then your vitamin D levels may fluctuate depending on the season. The levels may go down during the winter months, due to a lack of sufficient sunlight. This is why you'll find it common for those living in Melbourne to have low vitamin D levels but those living in Queensland rarely experience this issue
  • The elderly in particular suffer from this deficiency as their organs and skin additionally lose the capacity to efficiently produce vitamin D in the body. They most often become immobile, stay indoors and may have poor nutrition due to dentures
  • Breastfeeding infants born of a deficient mother will also have the deficiency
  • Without adequate sunshine, supplementation or eating from fortified dietary sources, vegans and vegetarians are also at risk of deficiency


Vitamin D is essential for optimal bone condition, your immune system and many other aspects of health. A deficiency can be quite common and may have severe health consequences for people in differing life stages and lifestyles.

Adequate sun exposure and consuming vitamin D2 and D3 through dietary sources is key to good health.


Anne-Sophie Rayment, Nutritional Advisor.



1. Bjarnadottir, (2017), How Much Vitamin D Should You Take For Optimal Health?, Retrieved from https://www.healthline.com/nutrition/how-much-vitamin-d-to-take#How-Common-Is-Vitamin-D-Deficiency?

2. R. Webb, L. Kline, M. F. Holick, (1988), Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin, DOI: 10.1210/jcem-67-2-373, retrieved from https://pubmed.ncbi.nlm.nih.gov/2839537/

3. Australian Government Department of Health, Daily nutrient requirements calculator, retrieved from https://www.eatforhealth.gov.au/node/1813927/done?sid=544108

4. F. DeLuca, Overview of general physiologic features and functions of vitamin D, Americal Journal Of Clinical Nutrition 80 (2004): 1689S-1696S.

5. M. Trang, D. E. Cole, L. A. Rubin, A. Pierratos, S. Siu, & R. Vieth, (1998), Evidence that vitamin D3 increases serum 25-hydroxyvitamin D more efficiently than does vitamin D2, DOI: 10.1093/ajcn/68.4.854, retrieved from https://pubmed.ncbi.nlm.nih.gov/9771862/

6. S. Adams & M. Hewison, (2008), Unexpected actions of vitamin D: new perspectives on the regulation of innate and adaptive immunity, DOI: 10.1038/ncpendmet0716, retrieved from https://pubmed.ncbi.nlm.nih.gov/18212810/

7. F. Holick, Sunlight and vitamin D for bone health and prevention of autoimmune diseases, Americal Journal Of Clinical Nutrition 80 (2004): 1678S-1688S.

8. J. Barger-Lux & Robert P Heaney, (2002), Effects of above average summer sun exposure on serum 25-hydroxyvitamin D and calcium absorption, DOI: 10.1210/jc.2002-020636 retrieved from https://pubmed.ncbi.nlm.nih.gov/12414856/

9. Tortora, G. J., Derrickson, B. H., Burkett, B., Dye, D., Cooke, J., Diversi, T., & Peoples, G. (2015). Principles of anatomy and physiology, (1st Asia-Pacific ed.), Milton, QLD, John Wiley & Sons Australia Ltd.

10. G. Tsiaras & M. A. Weinstock, (2011), Factors influencing vitamin D status, DOI: 10.2340/00015555-0980, retrieved from https://pubmed.ncbi.nlm.nih.gov/21384086/

11. Whitney, E. N., Rady, R. S., Crowe, T., & Walsh, A. (2017). Understanding nutrition - Australia and New Zealand Edition (3rd ed.). Melbourne, VIC: Cengage Learning.