Temporal trends in the US population's vitamin D status have been uncertain because of nonstandardized serum 25-hydroxyvitamin D [25(OH)D] measurements.Objective:
To accurately assess vitamin D status trends among those aged ≥12 y, we used data from the cross-sectional NHANESs.Design:
A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for measuring 25(OH)D (sum of 25-hydroxyvitamin D2 and 25-hydroxyvitamin D3), calibrated to standard reference materials, was used to predict LC-MS/MS-equivalent concentrations from radioimmunoassay data (1988–2006 surveys; n = 38,700) and to measure LC-MS/MS concentrations (2007–2010 surveys; n = 12,446). Weighted arithmetic means and the prevalence of 25(OH)D above or below cutoff concentrations were calculated to evaluate long-term trends.Results:
Overall, mean predicted 25(OH)D showed no time trend from 1988 to 2006, but during 2007–2010 the mean measured 25(OH)D was 5–6 nmol/L higher. Those groups who showed the largest 25(OH)D increases (7–11 nmol/L) were older, female, non-Hispanic white, and vitamin D supplement users. During 1988–2010, the proportions of persons with 25(OH)D <40 nmol/L were 14–18% (overall), 46–60% (non-Hispanic blacks), 21–28% (Mexican Americans), and 6–10% (non-Hispanic whites).Conclusions:
An accurate method for measuring 25(OH)D showed stable mean concentrations in the US population (1988–2006) and recent modest increases (2007–2010). Although it is unclear to what extent supplement usage compared with different laboratory methods explain the increases in 25(OH)D, the use of higher vitamin D supplement dosages coincided with the increase. Marked race-ethnic differences in 25(OH)D concentrations were apparent. These data provide the first standardized information about temporal trends in the vitamin D status of the US population.