FP31-3 Low Vitamin D Binding Protein May Contribute to Physiologically Important Hypovitaminosis D in Obese Adolescents

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: 10:55 AM
Room 130 (Moscone Center)

Poster Board MON-241
Noelle Summers Larson*1, Jill Ellen Emerick2, Candace Suzanne Staubitz Percival3, David Larson3, Cara H Olsen4, Karen Susan Vogt5, Ronald L Horst6, Steven Rothwell3 and Merrily Poth3
1Tripler Army Medical Center, Honolulu, HI, 2WRNMMC, Bethesda, MD, 3USUHS, Bethesda, MD, 4Uniformed Services University of Health Sciences, Bethesda, MD, 5Walter Reed National Military Me, Bethesda, MD, 6USDA ARS Nat Animal Disease, Ames, IA
Background: The association between obesity and low plasma 25 hydroxy-vitamin D (25 OHD) has been described in adult and pediatric populations. Neither the reason for these low levels nor their significance is clear. Vitamin D binding protein (VDBP) is the major carrier protein for 25 OHD and low levels may contribute to increased renal clearance of vitamin D. Hypovitaminosis D is associated with impaired insulin sensitivity in adults. This study was performed to determine if obese adolescents have lower VDBP levels that contribute to low circulating 25 OHD, and further, whether low 25 OHD is physiologically relevant to insulin sensitivity.
Methods: We measured fasting 25 OHD, PTH, VDBP, insulin and glucose in plasma of 34 obese and 23 non-obese adolescents, age 10-18 years. Subjects completed questionnaires regarding intake of dairy and vitamin D-containing supplements as well as sun exposure habits. We used elevated PTH and calculated HOMA-IR >3 as markers for relevant physiologic effects of low 25 OHD. We also examined the in vitro effect of 25 OHD on insulin sensitivity by isoproterenol induced lipolysis using purified human adipocytes.
Results: Our data agree with previous reports showing a negative association between BMI and plasma 25 OHD (p=0.003) that was not explained by differences in sun exposure or dietary intake. There was a positive correlation between VDBP and 25 OHD levels (p=0.002) and VDBP was inversely correlated with BMI (p=0.03). As expected, PTH levels were higher in vitamin D deficient subjects than those with 25 OHD D >20ng/mL (p=0.02). Subjects with HOMA-IR >3 had lower 25 OHD levels than insulin sensitive subjects. The addition of physiologic concentrations of 25 OHD to purified human adipocytes reduced glycerol release by approximately 20% at all concentrations (0.3, 1 and 3 micrograms per ml) of insulin, demonstrating that 25 OHD improved insulin sensitivity in human adipose cells.
Conclusions: Decreased plasma levels of VDBP in obese adolescents may contribute to vitamin D insufficiency and deficiency. Low vitamin D is related to elevated PTH and high HOMA-IR suggesting that this low 25 OHD has physiologically important effects. In addition, data from in vitro experiments using human adipose cells suggest a direct effect of 25 OHD on insulin sensitivity. These results support a possible role for ensuring normal levels of plasma vitamin D in preventing and treating insulin resistance.

Nothing to Disclose: NSL, JEE, CSSP, DL, CHO, KSV, RLH, SR, MP

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

Sources of Research Support: Diabetes Alternative Research and Healthcare Foundation, Grant #108 Awarded to NSL