Vitamin D has been the subject of intense interest in recent years, not only because
of its role in bone health, but also because of the potential link between vitamin
D status and the risk of cancer, diabetes, and other diseases. Considerable effort
has been devoted to examining the vitamin D exposure of various populations and determining
the levels of circulating vitamin D metabolites that are associated with optimal health.
Accurate assessment of vitamin D status is also important for identifying individuals
with vitamin D deficiencies and for effective treatment. However, the value of vitamin
D testing in these applications has been limited by poor comparability between different
methods for 25-hydroxyvitamin D [25(OH)D], the major circulating metabolite of vitamin
D. In addition, until recently, there was no mechanism to assess the accuracy of any
of the methods being used. The Analytical Chemistry Division at the National Institute
of Standards and Technology (NIST) is helping to ensure the accuracy and comparability
of 25(OH)D measurements through the development of reference methods and Standard
Reference Materials (SRMs) for vitamin D metabolites. SRM 972 Vitamin D in Human Serum,
and the subsequent SRM 972a Vitamin D Metabolites in Human Serum, represent the first
steps toward establishing an accuracy base for measurement of 25(OH)D in individuals
and across populations. Value assignment of these reference materials has been performed
using multiple higher-order methods. NIST has also initiated a measurement quality
assurance program for vitamin D metabolites to assist laboratories in improving accuracy
and comparability. Acknowledgements: Partial funding for this work was provided by the National Institutes of Health (NIH),
Office of Dietary Supplements (ODS) through an interagency agreement
