A study by Loyola University in Chicago suggests that as many as 80 million Americans may be unnecessarily taking vitamin D supplements. The study is one of many to support new vitamin D supplement recommendations by the Institute of Medicine, which changed the definition of a person with vitamin D deficiency from having blood levels lower than 30 nanograms per millileter (ng/mL) to 20 or less.
The researchers looked at data for more than 15,000 healthy adults from the third National Health and Nutrition Examination Survey. They compared that to 18 years of National Death Index data to see whether vitamin D levels affected the rate of death. Seventy percent had vitamin D levels deficient under the old guidelines, but only 30 percent under the new guidelines. The death rate was highest among those with vitamin D levels below 12 ng/mL compared with any other levels. The death rate was the same at levels between 20 and 40 ng/mL, supporting the lower deficiency threshold.