Vit D article in 2009 Journal of American Physicians and Surgeons

- A recent review concluded that 10,000 IU/d of D is safe in adults.  Some recommendations to achieve ≥50 ng/mL by supplementation exist.

- On the ≥20 ng/mL basis, it has been estimated that 1 billion people worldwide are D deficient. In Western countries, advice to avoid sun exposure and to use sunscreen
could be a major contributor to vitamin D deficiency. A lotion with a sun protection factor (SPF) of 8 can cut vitamin D synthesis by 92.5%, and one with a SPF of 15 by 99%.

- As recently as 2004, the results of three of five clinical laboratories did not match the accurate assays for 25-hydroxyvitamin D by the high-performance liquid chromatography method in an
academic lab. All three were too high, and one was more than twice as high (43 vs. 20 ng/mL).

Conclusion: Optimum vitamin D levels are usually seen only in people exposed to intense sunlight on their bare skin, which leads to a serum  25-hydroxyvitaminD level of 50-70 ng/mL.
Higher levels of vitamin D are strongly associated with prevention of falling and fractures from falling; lower incidence of cancer or cancer mortality; lower mortality from cardiovascular disease; fewer symptoms of colds or influenza; prevention of both types of diabetes, multiple sclerosis, chronic back pain, depression, and possibly autism. Toxicity is rare. Concomitant calcium ion supplementation was shown to be of value in many but not all trials. Risks for Vitamin D insufficiency (<30 ng/mL of 25-hydroxyvitamin D in serum) are: limited sun; dark skin; skin shielded from sunlight by glass, plastic, clothing or sunscreen lotion; and/or low vitamin D intake in diet. Prevention of deficiency by supplementation at 800-2,000 IU/d is practical. Repletion with Vitamin D at levels up to 10,000 IU/d or 50,000 IU/wk, then maintenance at lower levels, is feasible. A number of common drugs deplete vitamin D levels or may interfere with its biosynthesis catalyzed by sunlight. Vitamin D status is best monitored by at least annual assays of serum25-hydroxyvitaminD .