Threshold for effects of vitamin D deficiency on glucose metabolism in obese female African-American adolescents.
BACKGROUND
Vitamin D status can influence insulin resistance.


OBJECTIVE
The aim of the study was to determine the prevalence of vitamin D deficiency in obese African-American (AA) adolescent females in a southeastern latitude and to determine the relationship of 25-hydroxyvitamin D [25(OH)D] with insulin and glucose dynamics.


METHODS
We conducted a cross-sectional study in a University Children's Hospital.


METHODS
Serum 25(OH)D, fasting glucose, PTH, serum calcium, serum lipids, serum transaminases, and C-reactive protein were assessed. Indices of insulin sensitivity and resistance were determined from an oral glucose tolerance test. Subjects were classified as vitamin D deficient or sufficient, based on the traditional vitamin D deficiency definition [serum 25(OH)D <20 ng/ml] and also by a lower 25(OH)D cut-point of 15 ng/ml or less.


RESULTS
A total of 51 AA adolescent females (body mass index, 43.3 +/- 9.9 kg/m(2); age, 14 +/- 2 yr) were studied. Serum 25(OH)D concentrations were 20 ng/ml or less in 78.4% and 15 ng/ml or less in 60.8% of subjects. There were no significant group differences in the metabolic outcomes when subjects were classified using the traditional vitamin D deficiency definition. The Matsuda index of insulin sensitivity was significantly lower (P = 0.02), and insulin area under the curve was significantly higher (P = 0.04) in subjects with 25(OH)D concentrations of 15 ng/ml or less vs. those with higher concentrations.


CONCLUSIONS
Vitamin D deficiency is highly prevalent in obese, AA female adolescents and may promote insulin resistance. Our data suggest that a 25(OH)D concentration of 15 ng/ml or less may be the threshold by which vitamin D deficiency confers negative effects on insulin sensitivity.
Ashraf
Ambika
A
Department of Pediatrics/Division of Pediatric Endocrinology and Metabolism, Children's Hospital, University of Alabama at Birmingham, CPP 230, 1601 Fourth Avenue South, Birmingham, Alabama 35233, USA. AAshraf@peds.uab.edu
Alvarez
Jessica
J
Saenz
Karen
K
Gower
Barbara
B
McCormick
Kenneth
K
Franklin
Frank
F
D000293:Adolescent; D001741:Black or African American; D019540:Area Under Curve; D002648:Child; D003430:Cross-Sectional Studies; D005260:Female; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D007333:Insulin Resistance; D009765:Obesity / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000097:blood; D014807:Vitamin D / Q000031:analogs & derivatives / Q000097:blood; D014808:Vitamin D Deficiency / Q000378:metabolism*
D010281:Parathyroid Hormone; D014807:Vitamin D; C104450:25-hydroxyvitamin D; D005947:Glucose