Mean vitamin D concentrations among Americans remained stable between 1988–2006 and showed modest increases between 2007–2010. 

Trends in the U.S. population’s vitamin D status have been unclear due to non-standardized serum 25-hydroxyvitamin D (25[OH]D) measurements. Researchers from the National Institutes of Health (NIH) and the Centers for Disease Control and Prevention (CDC) set out to accurately assess vitamin D status trends among individuals aged ≥12 years using cross-sectional National Health and Nutrition Examination Survey (NHANES) data. 

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A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for measuring 25(OH)D was used to predict LC-MS/MS-equivalent concentrations from radioimmunoassay data from 1988–2006 (n=38,700) and to measure LC-MS/MS concentrations from 2007–2010 (n=12,446). Long-term trends were valuated through weighted arithmetic means and the prevalence of 25(OH)D above or below cutoff concentrations.

The mean predicted 25(OH)D levels showed no time trend from 1988–2006 but had a 5–6nmol/L higher mean concentration during 2007–2010. Patient groups with the largest 25(OH)D increases (7–11nmol/L) were older, female, non-Hispanic white, and vitamin D supplement users. Between 1988–2010, the proportion of individuals with 25(OHD) <40nmol/L were 14–18% overall, 46–60% non-Hispanic blacks, 21–28% Mexican Americans, and 6–10% non-Hispanic whites. 

Study authors noted that it is unclear to what extent supplement use explains the increases in 25(OH)D levels but higher vitamin D supplement use did correlate with the increase. Findings from this study offer the first standardized information about temporal trends in the vitamin D status of the U.S. population.  

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