FP31-4 Vitamin D binding protein is associated with fasting insulin and insulin sensitivity indices

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: FP31-Disorders of Vitamin D Metabolism & Action
Monday, June 17, 2013: 10:45 AM-11:15 AM
Presentation Start Time: 11:00 AM
Room 130 (Moscone Center)

Poster Board MON-242
Ambika P Ashraf*1, Carrie Huisingh2, Jessica Alejandra Alvarez3 and Barbara Ann Gower4
1University of Alabama School of Medicine, Birmingham, AL, 2University of Alabama at Birmingham, 3Emory University School of Medicine, Atlanta, GA, 4Univ of AL at Birmingham, Birmingham, AL
Background: Vitamin D binding protein (VDBP) and albumin determines the serum concentration of free 25-hydroxy vitamin D (25OHD). Considering the fact that a very similar binding protein such as sex hormone binding globulin is influenced significantly by insulin resistance, we hypothesized the VDBP would also be regulated by fasting insulin and insulin resistance status. Our primary objective is to determine serum concentrations of total 25OHD, free 25OHD and VDBP in a cohort of healthy, non-obese adolescents and to assess the concentration of free 25OHD and VDBP according to vitamin D deficiency / sufficiency/ adequacy status.  The secondary objective is to evaluate the associations between VDBP to insulin measures derived from a mixed meal tolerance test (MMTT).
Subjects and Methods: This was a cross sectional study (NCT01041365) of n = 49 non-obese, post menarchal, female adolescents, ages 14-18 years. Serum total 25OHD was stratified as <20 ng/ml, 20-29 ng/ml and >30 ng/ml. Results: In each group, the mean serum total 25OHD was 12.8 ± 4.4 vs. 23.6 ± 2.7 vs. 34.3 ± 6.3 ng/ml; free vitamin D was 86.1 ± 30.2 vs. 162.7 ± 27.6 vs. 228.4 ± 38.9 pmol/l; and VDBP was 108.8 ±  52.7 vs. 181.3 ±  79.2 vs. 234.2 ±  51.8 ng/ml, respectively.  Total 25OHD was strongly associated with free 25OHD (Rho=0.98, P-value= <0.0001). There was strong positive correlation between VDBP and total 25OHD (rho=0.57, P<0.0001) and free 25OHD (rho=0.52, P=0.0002). Both total and free 25OHD were negatively associated with HOMA IR (Rho= -0.42, P -value= 0.003 and Rho= -0.45, P -value= 0.001 respectively) and positively with whole body insulin sensitivity (WBISI, Rho= 0.37, P -value= 0.01 and Rho= 0.39, P -value= 0.006). VDBP was associated with HOMA IR (Rho= -0.51, P -value= 0.0003), fasting insulin (Rho= -0.51, P -value= 0.0003), and positively associated with WBISI (Rho= 0.33, P -value= 0.03).The association between VDBP and insulin measures persisted after adjusting for percent body fat.
Conclusion: The strong positive correlation between total 25OHD, free vitamin D and VDBP indicates that synthesis of 25OHD is responsive to circulating concentration of free vitamin D and VDBP. Thus, when serum total 25OHD is lower, the serum VDBP and free 25OHD concentrations are lower. Moreover, results suggest that VDBP is regulated by fasting insulin and insulin resistance status and hence, VDBP concentration could be lower in hyperinsulinemic or insulin resistant states, which in turn could partly account for lower serum vitamin D concentrations seen in obesity.

Nothing to Disclose: APA, CH, JAA, BAG

*Please take note of The Endocrine Society's News Embargo Policy at http://www.endo-society.org/endo2013/media.cfm

Sources of Research Support: This study was funded by Child Health Research Center Grant K12 HD043397 (T0909180013), and was supported by the Center for Clinical and Translational Science (5UL1 RR025777). Ambika Ashraf is supported in part by University of Alabama Minority Health Center.