AIS shopCareers

What is it?

  • Vitamin D is classified as a fat soluble vitamin which acts functionally as a hormone and has a structure that is similar to steroid hormones.
  • There are two different isoforms of Vitamin D: D3 (cholecalciferol), which is the important isomer formed in human skin and D2 (ergocalciferol), which is the plant-derived equivalent. D2 was the first isoform to be characterised and was first used in Vitamin D supplements and for food fortification. D3 is now considered preferable. D3 is biologically inert until converted in the liver to 25(OH)D and to 1,25(OH)D in the kidney.1
  • Vitamin D plays an important role in calcium and phosphate homeostasis (bone health), gene expression and cell growth. The recent recognition of Vitamin D receptors in most body tissues indicates a role for Vitamin D in many aspects of health and normal function. Vitamin D is now known to be important for optimal muscle function.
  • The principal source of circulating Vitamin D comes from exposure to ultraviolet B (UVB) radiation from sunlight.
  • In 2010, the Institute of Medicine issued new Dietary Reference Intakes for Vitamin D, assuming no sunlight exposure; this included a Recommended Dietary Intake of 600 IU/d and an upper-Level intake of 4000 IU/d (www.ncbi.nlm.nih.gov/books/NBK56070/pdf/Bookshelf_ NBK56070.pdf, opens in a new tab). The Australian Government Department of Health and the New Zealand Ministry of Health developed a Methodological Framework in 2015 to guide future reviews of priority Nutrient Reference Values (NRVs). Assuming no sunlight exposure, the adequate intake for Vitamin D in Australia is estimated to be 5 – 15 mcg/day (200 – 600 IU/day), depending on age and sex (www.nrv.gov.au/nutrients/vitamin-d, opens in a new tab).
  • Vitamin D deficiency can lead to several health issues including increased risk of bone injuries, chronic musculoskeletal pain and viral respiratory tract infections.
  • There is also emerging evidence that supplementing Vitamin D in athletes with sub-optimal Vitamin D levels may have beneficial effects on athletic performance, especially in relation to strength, power, reaction time and balance.2-5
  • There is no universally accepted definition of Vitamin D deficiency however, the following definitions based on serum levels of 25(OH) Vitamin D are often cited and have the most clinical utility:*Higher status may be preferred for athletes to allow a greater safety margin and to optimize performance; some agencies working with elite athletes often set their own thresholds for desired Vitamin D concentrations.
    • Vitamin D deficiency: serum levels < 20 ng/ml (50 nmol/L)
    • Vitamin D insufficiency: serum levels < 30 ng/ml (75 nmol/L)
    • Vitamin D sufficiency: serum levels > 30 ng/ml (75 nmol/L)
    • Ideal Vitamin D range*: 75-120 nmol/L
    • Toxicity: > 375 nmol/L when combined with raised serum calcium
  • Several recent studies have shown low levels of vitamin D among athletes.6-8

Back to top