OR45-5 Higher Levels of 25-Hydroxyvitamin D Following New Vitamin D Intake Guidelines

Program: Abstracts - Orals, Poster Previews, and Posters
Session: OR45-What Is New in Vitamin D?
Sunday, March 8, 2015: 9:30 AM-11:00 AM
Presentation Start Time: 10:30 AM
Room 29 (San Diego Convention Center)
Peng Wang, MD, PhD1, JoDell E Wilson, Ph.D.2, Weijia (William) Wu, PhD3 and Patrick William Mason, MD, PHD3
1Medstar Georgetown University Hospital, Washington, DC, 2Quest Diagnostics, 3Quest Diagnostics, Chantilly, VA
Background. 25-hydroxyvitamin D (25(OH)D) determinations are used to determine vitamin D status: deficient <20, insufficient 20-29, and  optimal  30-100 ng/mL (Holick, JCEM 2011). Approximately 77% of US adults have suboptimal vitamin D levels, based on NHANES 2001-2004 data (Ginde, Arch Intern Med, 2009). The Institute of Medicine (IOM, 2010) and the Endocrine Society (Holick, JCEM 2011) recently recommended increased vitamin D dietary reference intake. Additionally, vitamin D3 (cholecalciferol) became more readily available as the main form of vitamin D supplement, and at higher doses. Between 2002 and 2011, sales of vitamin D supplements jumped >10x—from $42 million to $605 million (Nutrition Business Journal 2014 Supplement Business Report). To investigate changes in vitamin D levels after the guideline updates and increases in vitamin D3 supplementation, we analyzed vitamin D results for all adults tested in a national reference laboratory (Quest Diagnostics Nichols Institute, Chantilly, VA) during a 12-month period in 2009-2010 (pre-guidelines) and 2013-2014 (post-guidelines). Additionally, the suppression effects of 25(OH)D on intact parathyroid hormone (iPTH) levels, we evaluated iPTH in  the two study periods.   

Method. Total 25(OH)D was determined using liquid chromatography—tandem mass spectrometry. We evaluated all 25(OH)D tests performed for adults (≥18 years old) for a 12-month period starting in November 2009 (1.6 million tests)  and August 2013 (1.2 million tests). Intact PTH was measured by a chemiluminescence-based assay. The results were compared using Z-test after Box-Cox transformation to satisfy the Gaussian distribution assumption.

Results. The mean 25(OH)D value increased from 27.2±0.02 ng/mL pre-guidelines to 32.5±0.03 ng/mL post-guidelines (P <0.0001). The proportion of patients with deficient vitamin D levels decreased significantly from the pre-guideline period to the post-guideline period (22.1% vs 14.5%), as did the proportion with insufficient levels (33.7% pre-guidelines vs 28.1% post-guidelines) (both P <0.0001). No clinically significant changes in vitamin D2 levels were noted between pre- and post-guideline groups. The percentage of iPTH results above the upper limit of the reference range decreased from 50% in 2009 to 39% in 2014 (P <0.0001).

Conclusion. We observed an increase in the mean value of 25(OH)D in the adult population, with concomitant decreases in the percentage of patient specimens classified as deficient or insufficient 25(OH)D post-guidelines. Possible explanations for these results include 1) a positive impact on patient 25(OH)D concentrations after introduction of the new guidelines; or 2) testing may have shifted to people who were more likely to have optimal levels of 25(OH)D in the post-guideline period. The fall in the percent of elevated iPTH results corresponds, as expected, to the rise in the 25(OH)D levels.

Nothing to Disclose: PW, JEW, WW, PWM

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