1. Most OTC (over the counter) vitamin D is D3. Prescription vitamin D is D2. Both work, and they both are made more active by the liver and then kidneys.
2. Food sources are too low to help (exception: 1 Tbs. cod liver oil has 1360 I.U.). The major source of vitamin D in humans comes from synthesis in the skin after exposure to UVB rays from the sun.
3. People living in northern-latitude states usually test low. Washington's best vitamin-D-producing months are June, July (especially), and August. As a rule of thumb, if your shadow is longer than your height, you will not make vitamin D even if you get some tan.
4. All sunscreens block vitamin D production.
5. About half of my new patients understand that vitamin D helps calcium absorption and therefore bone density. Very few know that it benefits the immune and nervous systems, too.
6. The most common vitamin D test is for one of its forms, 25 OH vitamin D. The normal range is usually given as 30-150. Research and clinical experience strongly suggest that the ideal range is about 70-110. My colleagues and I, who test both before and after supplementation, are finding the vast majority of patients in Washington needing the following approximate vitamin D3 daily doses:
Women: 4000-6000 I.U.
Men: 5000-8000 I.U.
One's size, bone density, and liver status need to be considered too. People who test under 30 (e.g. 6-25) often need at least 10,000 I.U. D3 daily supplement for a few weeks to raise their levels from low to ideal. Testing helps us to be precise and to individualize doses.
As an aside, the liquid and softgel forms of D3 seem to absorb better than tablets. Our pharmacy carries a liquid D3 (in olive oil) for $20/year, and our softgel form costs about $45 for a year's supply.
My next blog post on vitamin D3 will review some more specifics about its benefits on immunity and nerves.