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Original research
Serum 25OHD concentration as a predictor of haemoglobin A1c among adults living in the USA: NHANES 2003 to 2010
  1. Michele Nicolo1 and
  2. Joseph I Boullata2
  1. 1 Keck School of Medicine, University of Southern California, Los Angeles, California, USA
  2. 2 Nutrition Sciences, Drexel University, Philadelphia, Pennsylvania, USA
  1. Correspondence to Dr Michele Nicolo, University of Southern California, Los Angeles, CA 90007, USA; mnicolo{at}usc.edu

Abstract

Background Vitamin D status influences glucose metabolism. Serum 25-hydroxyvitamin D (25OHD) concentrations have been inversely associated with type 2 diabetes risk. The optimal serum 25OHD level needed for adequate glycaemic control is unknown.

Objective To determine the relationship among serum 25OHD concentrations and degree of glucose regulation using percentage of haemoglobin A1c (HbA1c%).

Methods Data for adults ≥ 20 years from the National Health and Nutrition Examination Survey (NHANES) (2003–2010) were included. A binary logistic regression was used for serum 25OHD (nmol/L) as a continuous variable to determine the OR and 95% CI for HbA1c >6.5%, adjusting for sex, race and body mass index (BMI). Measures of serum 25OHD were grouped into quartiles and entered into a binary logistic regression model to determine the OR and 95% CI for HbA1c >6.5% in an adjusted model.

Results Across all NHANES cycles, lower serum 25OHD was associated with greater odds of HbA1c ≥ 6.5% when adjusting for sex, race, age and BMI (NHANES 2003–2004 (N=4402): OR 0.985, 95% CI 0.979 to 0.990; NHANES 2005–2006 (N=4409): OR 0.976, 95% CI 0.969 to 0.982; NHANES 2007–2008 (N=4525): OR 0.989, 95% CI 0.984 to 0.993; and NHANES 2009–2010 (N=5660): OR 0.988, 95% CI 0.984 to 0.991). In an adjusted model, the lowest quartile of serum 25OHD (0–41 nmol/L, N=4879) was associated with greater odds of HbA1c ≥ 6.5% compared with the highest quartile (73–260 nmol/L, N=4472), OR 2.37, 95% CI 2.03 to 2.77. The odds of HbA1c ≥ 6.5% were also greater for adults with serum 25OHD considered to be sufficient compared with the highest quartile, OR 1.68, 95% CI 1.56 to 1.61).

Conclusion Lower serum 25OHD concentrations are associated with poor glycaemic control (HbA1c ≥ 6.5%). Sufficient serum 25OHD levels were also associated with poorer blood glucose control. Further research is needed to investigate an optimal serum concentration or threshold to support adequate blood glucose control.

  • serum 25ohd
  • hemoglobin a1c

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/.

https://doi.org/10.1136/bmjnph-2019-000029

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    Footnotes

    • Contributors MN analysed the data and wrote the manuscript. JIB contributed to manuscript editing, the study design and manuscript revisions. All authors contributed to the critical interpretation of the results, reviewed the manuscript for important intellectual content and approved the final version of the manuscript. MN is the guarantor of this work and, as such, had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.

    • Funding MN was supported by a grant from the National Institutes of Health, USA (T32CA009492-34).

    • Competing interests None declared.

    • Patient consent for publication Not required.

    • Provenance and peer review Not commissioned; externally peer reviewed.

    • Data availability statement Data are available in a public, open-access repository.