Vitamin D: An Updated Clinical Perspective

Alarming statistics have been emphasized through research findings and the media concerning a global crisis of vitamin D deficiency. Severe vitamin D deficiency is clinically defined as 25(OH)D <30 nmol/L (or 12 ng/mL). Prevalence rates in the United States of a severe vitamin D deficiency have been reported as 5.9%, 7.4% in Canada, and 13% in Europe. Prevalence of 25(OH)D levels <50 nmol/L (or 20 ng/mL) have been estimated to be 24% in the United States, 37% in Canada, and 40% in Europe. These numbers could be a reflection of the dramatic increase in vitamin D testing, large variability in mean serum 25(OH)D which can vary up to 300%, analytic procedures utilized to determine 25(OH)D, or even variable among the available assays. For example, there was more than a 50-fold increase in the incidence of testing for vitamin D deficiency in UK primary care between 2005 and 2015.12 Other countries have also demonstrated a substantial increase in vitamin D testing. In light of this, The Endocrine Society has published clinical guidelines on testing for vitamin D deficiency. Only those at risk for developing a vitamin D deficiency are recommended to be tested, and population screening or screening those not at risk is contraindicated. Regardless of which factors might be contributing to a vitamin D deficiency, most of the population is in fact, not deficient in vitamin D. Current data indicates that serum 25(OH)D levels in the general United States population have increased over the last decade (2007-2017). Public health campaigns increasing awareness, expanded testing, association with diseases, and roles beyond bone health have played important roles in reversing this trend. This presents an important opportunity to revisit vitamin D.