Modeling a methylmalonic acid-derived change point for serum vitamin B-12 for adults in NHANES

Regan L. Bailey, Ramon A. Durazo-Arvizu, Ralph Carmel, Ralph Green, Christine M. Pfeiffer, Christopher T. Sempos, Alicia Carriquiry, Elizabeth A. Yetley

Research output: Contribution to journalArticle

24 Scopus citations

Abstract

Background: No consensus exists about which cutoff point should be applied for serum vitamin B-12 (SB-12) concentrations to define vitamin B-12 status in population-based research. Objective: The study's aim was to identify whether a change point exists at which the relation between plasma methylmalonic acid (MMA) and SB-12 changes slope to differentiate between inadequate and adequate vitamin B-12 status by using various statistical models. Design:We used data on adults (≥19 y; n = 12,683) from NHANES 1999-2004- A nationally representative, cross-sectional survey. We evaluated 6 piece-wise polynomial and exponential decay models that used different control levels for known covariates. Results: The MMA-defined change point for SB-12 varied depending on the statistical model used. A linear-splines model was determined to best fit the data, as determined by the approximate permutation test; 3 slopes relating SB-12 and MMA and resulting in 2 change points and 3 subgroups were shown. The first group (SB-12 <126 pmol/L) was small and had the highest MMA concentration (median: 281 nmol/L; 95% CI: 245, 366 nmol/L; n = 157, 1.2%); many in this group could be considered at high risk of severe deficiency because combined abnormalities of MMA and homocysteine were very frequent and the concentrations themselves were significantly higher. The highest SB-12 group (SB-12 >287 pmol/ L; n = 8569, 67.6%) likely had adequate vitamin B-12 status (median MMA: 120 nmol/L; 95% CI: 119, 125 nmol/L). The vitamin B-12 status of the sizable intermediate group (n = 3957, 33%) was difficult to interpret. Conclusions: The 3 distinct slopes for the relation between SB-12 and MMA challenges the conventional use of one cutoff point for classifying vitamin B-12 status. In epidemiologic research, the use of one cutoff point would fail to separate the small, severely deficient group from the intermediate group that has neither normal nor clearly deficient vitamin B-12 concentrations (ie, unknown vitamin B-12 status). This intermediate group requires further characterization.

Original languageEnglish (US)
Pages (from-to)460-467
Number of pages8
JournalAmerican Journal of Clinical Nutrition
Volume98
Issue number2
DOIs
StatePublished - Aug 1 2013

ASJC Scopus subject areas

  • Medicine (miscellaneous)
  • Nutrition and Dietetics

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    Bailey, R. L., Durazo-Arvizu, R. A., Carmel, R., Green, R., Pfeiffer, C. M., Sempos, C. T., Carriquiry, A., & Yetley, E. A. (2013). Modeling a methylmalonic acid-derived change point for serum vitamin B-12 for adults in NHANES. American Journal of Clinical Nutrition, 98(2), 460-467. https://doi.org/10.3945/ajcn.113.061234