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Am J Clin Nutr. 2013 Jun;97(6):1243-51. doi: 10.3945/ajcn.112.054502. Epub 2013 Apr 24.

Estimating mean annual 25-hydroxyvitamin D concentrations from single measurements: the Multi-Ethnic Study of Atherosclerosis.

Author information

1
Kidney Research Institute and Division of Nephrology, University of Washington, Seattle, WA, USA. sachsmc@u.washington.edu

Abstract

BACKGROUND:

The seasonal variation in circulating 25-hydroxyvitamin D [25(OH)D] concentrations is large relative to mean values. Single measurements may misclassify annual exposure, which may lead to bias in research and complicate clinical decision making.

OBJECTIVE:

We aimed to develop and validate a model for adjusting a single measurement of a serum 25(OH)D concentration to the time of year it was measured.

DESIGN:

We measured serum 25(OH)D concentrations by using mass spectrometry in 6476 participants from the Multi-Ethnic Study of Atherosclerosis at baseline and again in a subset of 368 participants at a median of 17 mo later. We estimated a cosinor model to describe the seasonal variability in 25(OH)D concentrations and evaluated this model by using follow-up 25(OH)D measurements.

RESULTS:

The mean age of subjects was 62.1 y, 61.2% of participants were nonwhite, and 53.3% of participants were women. The cosinor model predicted follow-up 25(OH)D concentrations better than a single measurement [difference in root mean squared error (RMSE): 1.3 ng/mL; P< 0.001]. The cosinor model also better predicted the measured annual mean 25(OH)D concentration (difference in RMSE: 1.0 ng/mL; P< 0.001). Annual mean 25(OH)D concentrations estimated from the cosinor model reclassified 7.1% of participants with regard to 25(OH)D deficiency, which was defined as <20 ng/mL. An estimated annual mean 25(OH)D concentration <20 ng/mL was significantly associated with lower bone mineral density, whereas an untransformed 25(OH)D concentration <20 ng/mL was not.

CONCLUSIONS:

Cross-sectional data can be used to estimate subject-specific mean annual 25(OH)D concentrations from single values by using a cosinor model. The tool we developed by using this approach may assist research and clinical care of adults in North America by reducing the misclassification of 25(OH)D deficiency.

PMID:
23615830
PMCID:
PMC3652923
DOI:
10.3945/ajcn.112.054502
[Indexed for MEDLINE]
Free PMC Article
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