Vitamin D Questions

It was time for the usual blood tests for cholesterol and such. I asked my doctor if it would be a good idea to get my Vitamin D levels checked too. There have been many studies recently that have shown vitamin D to be helpful in preventing certain cancers. I wondered... Did I have enough?

From what I understand, the best ways to get Vitamin D are from food sources or the sun. Vitamin D is synthesized from cholesterol found in foods like wild salmon. Vitamin D is also synthesized by the body when the sun's UVB rays hit bare skin.

Why is the recommended supplement is called D3? Well, it turns out that the name Vitamin D is a little imprecise. Vitamin D is actually a group of steroid molecules:

• There's bioactive D called calcitriol,
  
• The plant form or D2 called ergosterol,
  
• and D3 or the kind we synthesize in our skin called cholecalciferol.

That explains D3. How does a supplement help? To understand this it turns out I had to understand some rather dry, but interesting physiology. Here's my diluted version:

1. The first product of the sun and skin synthesis is called cholecalciferol.
2. Cholcalciferol travels to the liver where it is metabolized into calcidiol or 25(OH)D. Calcidiol is the storage form of Vitamin D and this is what is checked in Vitamin D blood tests.
3. Calcidiol can then take one of two pathways. However, the primary pathway is to the kidneys where it is converted to a steroid called calcitriol. This controls blood calcium levels and is critical to our survival. That's why it's the primary pathway.

A secondary pathway that calcidiol can travel is to our tissues, but only if there is any left after pathway one. This is why experts are stressing the importance of having enough circulating Vitamin D. Recent research shows that this calcitriol is used to defend the body's cells, provide immune function, reduce inflammation and may even fight cancer. If you're interested in more detail, you can find some great info from the National Cancer Institute about calcitriol here.

Unfortunately, it looks like many of us may not get enough Vitamin D from the sun or from foods. That's where the need for supplementation comes in. But how much? There's a lot of variation on this right now. The University of California at San Diego has an interesting discussion about current recommendations for Vitamin D levels. Just click on the title post to view the video.

Sources:
National Institutes of Health, Office of Dietary Supplements - http://ods.od.nih.gov/factsheets/vitamind.asp
The Vitamin D Council - http://www.vitamindcouncil.org/vitamin-d-healthcare-professionals/
American Journal of Clinical Nutrition - http://www.ajcn.org/cgi/content/abstract/85/6/1586
Colorado State Endocrine Index - http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/vitamind.html