In 2010 the “Optimal” level most often quoted at National Osteoporosis Foundation and at American Society for Bone Mineral Research was 32 to 100ng/ml. This is markedly different from the original “normal” range of 15 to 40ng/ml. Not all testing laboratories have adjusted their standard values. Some labs still report 30 or 25 or even 20 ng/ml as “normal”.
In individuals with less than 32 ng/ml of 25-hydroxy Vitamin D, the Bone Mineral Density drops rapidly and the Risk of Fracture rises rapidly. Less than 32ng/ml is considered “Insufficient”.
Less than 20 ng/ml is called Deficient and is associated with high Risk of Fracture. The result <6 ng/ml indicates a level too low to even detect.
Individuals with all day, year round exposure to tropical sun usually have 25-hydroxy vitamin D levels between 90 and 100 ng/ml. This strongly suggests that more than 100ng/ml is not needed.
We now aim for between 40 and 70 ng/ml when we Test for Vitamin D Level. We also take into account the time of year of the test since most individuals get some Vitamin D from the sunshine in the summer and drop their values by 10 or 20 ng/ml between September and March.
Vitamin D toxicity in an adult is extremely rare, even at levels far above 100ng/ml. Possible toxicity has been reported in individuals with blood levels above 500 ng/ml. The lowest dose reported to have resulted in toxicity in an adult was 10,000 IU daily for well past 6 months.
Jay Ginther, MD
2008 / Revised November 2010