After Vitamin D has been synthesized (this is the skin's response to sunlight), in the kidneys/liver it is converted to its active form. Active vitamin D regulates Ca2+ metabolism. In the gut, Vitamin D encourages Ca2+ uptake and simulatenously reducing the amount of reducing the excretion of Ca2+ in the kidneys .
Vitamin D is one of many very important vitamins that our bodies need to stay fit and healthy. Most people don't even realise or know that we gain the majority of vitamin D from direct sunlight on our skin. However, it is also found in some foods and a combination of a good diet and enough time out in the sun and our bodies will recieve enough to function at a healthy and normal level.
Vitamin D is required to mainly help regulate calcium levels within the body and therefore bone health. As more research is undergone we are starting to believe 'vitamin D deficiencies may be linked to various cancers' 
- ↑ Molecular Biology of the Cell, 5th ed. B Alberts, A Johnson, J Lewis, M Raff, K Roberts, P Walter. Published by Gardland Science, Taylor &amp; Franci Group, New York, 2008.
- ↑ Editorial(2002) A dose of vitamin D history. Nature structural biology. 9 (2), 77.
- ↑ Nature Reviews Cancer 7, 684-700 (September 2007) by Kristin K et al.