Through the National Health and Nutrition Examination Surveys (NHANES), the National Center for Health Statistics (NCHS) provides national data on the vitamin D status of the U.S. population. There is an apparent increase in prevalence of values for 25 hydroxyvitamin D (25(OH)D) at the low end of the range from NHANES III (1988–1994) to continuous NHANES (2000-2006), as a result of drift in the assay used to measure vitamin D status.
A Data Advisory entitled
Analytical Note for NHANES 2000-2006 and NHANES III (1988-1994) 25 Hydroxyvitamin D Analysis is now available from NCHS. This Advisory is published by NCHS regarding two issues that should be addressed when analyzing and using serum 25(OH)D data from NHANES. The two issues identified and described in this Advisory caution that changes in 25(OH)D over time are due, in part, to methodological artifacts that need to be considered when evaluating whether, and how much, differences over time are due to true changes in the vitamin D status of the US population.
The Data Advisory is available at
http://www.cdc.gov/nchs/data/nhanes/nhanes3/VitaminD_analyticnote.pdf
.