What does vitamin D actually do?
Vitamin D is an important nutrient which promotes normal immune system function and is associated with a healthy infant birth weight.[1] Perhaps the primary, and most well-known, function of vitamin D is that it helps the body absorb and use calcium,[2,3] an essential component of strong bones and teeth. A deficiency in calcium can lead to osteoporosis later in life.
How do we get vitamin D?
The main way we get vitamin D is through sun exposure, although you can also find a small amount in fatty fish and fish oils. It is difficult to get enough vitamin D through diet alone, so those with limited sun exposure may benefit from a supplement.
People who tend not to have enough sun exposure to make sufficient amounts of vitamin D include:
- people who work indoors for long periods
- people who cover their skin for cultural or religious reasons
- fair people who avoid sun exposure due to risk of burning
- people with darker skin
- people who live in southern areas of Australia (there may not be enough sun in winter in these areas)
- people with an increased need, such as the elderly and pregnant women.
How does vitamin K help?
Vitamin K helps to control the amount of vitamin D made by the body and keep it in homeostasis (this means keeping the amount stable so that the body has enough vitamin D, without making too much).
- Vitamin K activates a protein which moves calcium from the blood and into the bones and teeth.
- Once the level of calcium in the blood drops, the body makes more vitamin D.
- More calcium is absorbed and goes back into the blood stream.
- The cycle repeats.
If blood calcium levels get too high, the body stops making vitamin D which could lead to deficiency.[4]
What about other vitamins and minerals?
Other nutrients also act as cofactors for vitamin D, meaning they help the body use or absorb the vitamin, including magnesium, boron, zinc and vitamin A.
Magnesium is used in many of the enzymes which help the body use vitamin D,[5] and boron increases the level of vitamin D in the blood.[6]
Both zinc and vitamin A are involved in the vitamin D receptors - these are special areas in the cell that vitamin D ‘fits’ into (like a lock and key) and act like an on switch for a particular activity in the cell. Zinc is a component of the receptor itself,[7] while vitamin A increases the number of vitamin D receptors.[8]
Receptors are found in over 36 areas of the body — not just the bones but immune cells, ovaries, placenta, testes and uterus, demonstrating the importance of vitamin D throughout the whole body.[9]
References
- Scholl TO, Chen X. Vitamin D intake during pregnancy: association with maternal characteristics and infant birth weight. Early Hum Dev 2009;85(4):231-234. [Abstract]
- NHMRC. Vitamin D, 2014. Viewed 6 June 2017, https://www.nrv.gov.au/nutrients/vitamin-d
- Braun L, Cohen M. Herbs and natural supplements, 3rd ed, 2010. Elsevier Churchill Livingstone: Sydney.
- Vitamin K2. Altern Med Rev 2009;14(3):284-293. [Full text]
- Matsuzaki H, Katsumata S, Kajita Y, et al. Magnesium deficiency regulates vitamin D metabolizing enzymes and type II sodium-phosphate cotransporter mRNA expression in rats. Magnes Res 2013;26(2):83-86. [Full text]
- Pizzorno L. Nothing boring about boron. Integr Med (Encinitas) 2015;14(4):35-48. [Full text]
- Wan LY, Zhang YQ, Chen MD, et al. Relationship of structure and function of DNA-binding domain in vitamin D receptor. Molecules 2015;20(7):12389-12399. [Full text]
- Ng KY, Ma MT, Leung KK, et al. Vitamin D and vitamin A receptor expression and the proliferative effects of ligand activation of these receptors on the development of pancreatic progenitor cells derived from human fetal pancreas. Stem Cell Rev Rep 2011;7(1):53-63. [Abstract]
- Norman AW. From vitamin D to hormone D: fundamentals of the vitamin D endocrine system essential for good health. Am J Clin Nutr 2008;88(2):491S-499S. [Full text]
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