My book cites research from over 800 medical/scientific journals research that consistently demonstrates a direct correlation between vitamin D deficiency and more than one hundred diseases and disorders. Only those whose heads are buried in the sand could believe that optimal levels of D are not necessary for excellent health. However, along with vitamin D’s newfound popularity, there is bewilderment about what is “optimal.”
What is the optimal level of vitamin D?
Dr. Bruce Hollis and his colleagues conducted research in which they determined that no circulating vitamin D3 can be measured in the blood until 25(OH)D levels are greater than 40-50 ng/ml. This means that all vitamin D3 is used by the tissues to make 25(OH)D until the level is greater than 40-50. At that point, vitamin D3 begins to be measurable, meaning that the tissues are no longer so “hungry” for D3 that they use up every molecule made by the skin or taken orally. Therefore, optimal levels are probably somewhere over 50. Dr. John Cannell and I, in researching our book on vitamin D and athletics, found that athletic performance improves up to about 50-60 ng/ml and declines slightly at higher levels. In addition, a recent study showed that those with high vitamin D levels lived 26% longer than those with low levels; however, beyond 50 ng/ml, higher levels did not confer further advantage.
How much vitamin D does it take to produce the optimal level of 50-60?
Each intake of 100 IU per day of supplementation raises the blood levels of vitamin D about 1 ng/ml. Therefore, if there were no sun exposure or a source of dietary vitamin D, it would require 5,000 IU of supplemental D3 per day to achieve a level of 50. This rule of thumb, of course, varies according to the size of the person; a large person will require more vitamin D than a small person. It is also interesting to note that men who have high levels of vitamin D (due to outdoor summer activity) must take 5,000 IU during winter to maintain those levels.
A special case: nursing mothers
Nursing mothers must furnish sufficient vitamin D3 for themselves and their babies; if they are deficient, the babies have a greater risk of autism, schizophrenia and osteoporosis as they grow older. Dr. Hollis and his colleagues have demonstrated that nursing women need at least 6,400 IU per day to maintain adequate levels of 25(OH)D in both mother and child.
Remember that in Caucasian skin, twenty minutes of full-body sunlight exposure (both sides) will produce from 10,000-20,000 IU of vitamin D. A good tanning bed will produce about 10,000 IU in ten minutes. In either case, be sure not to burn.
Hopefully, this information has reduced any confusion about optimal levels of vitamin D and how to maintain them. Get those levels up to 50-60 ng/ml!
 Hollis, B. et al. Circulating Vitamin D3 and 25-hydroxyvitamin D in Humans: An Important Tool to Define Adequate Nutritional Vitamin D Status. J Steroid Biochem Mol Biol. 2007 March; 103(3-5): 631–634.
 Melamed, M. et al. 25-hydroxyvitamin D levels and the risk of mortality in the general population. Arch Intern Med. 2008 Aug 11;168(15):1629-37.
 Heaney, R. et al. Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Am J Clin Nutr 2003;77:204-10.
Wagner C. et al. High-dose vitamin D3 supplementation in a cohort of breastfeeding mothers and their infants: a 6-month follow-up pilot study. Breastfeed Med. 2006;1:59-70.