(01-12-10) Serum 25-hydroxyvitamin D and parathyroid hormone are independent determinants of whole-body insulin sensitivity in women...

Serum 25-hydroxyvitamin D and parathyroid hormone are independent determinants of whole-body insulin sensitivity in women and may contribute to lower insulin sensitivity in African Americans1,2,3

1. Jessica A Alvarez,
2. Ambika P Ashraf,
3. Gary R Hunter, and
4. Barbara A Gower
+ Author Affiliations
1. 1From the Departments of Nutrition Sciences (JAA and BAG) and Human Studies (APA) and the Department of Pediatrics/Division of Pediatric Endocrinology and Metabolism, The Children's Hospital (GRH), University of Alabama at Birmingham, Birmingham, AL.
? ↵2 Supported by grants P60-DK079626, R01-DK58278, R01-DK49779, R01-DK51684, M01-RR-00032, P30-DK56336, and UL1RR025777 from the National Institutes of Health. JAA is supported by the American Heart Association (Greater Southeast Affiliate). APA is supported, in part, by grant K12 HD043397 from the Child Health Research Center and a grant from the Diabetes Research Training Center.
? ↵3 Address correspondence to J Alvarez, Clinical Research Unit, JT1566, 625 19th Street South, Birmingham, AL 35233. E-mail: [email protected].
Abstract
Background: Circulating 25-hydroxyvitamin D [25(OH)D] and parathyroid hormone (PTH) concentrations have been shown to be associated with insulin sensitivity; however, adiposity may confound this relation. Furthermore, African Americans (AAs) have lower insulin sensitivity and 25(OH)D concentrations than do European Americans (EAs); whether these differences are associated in a cause-and-effect manner has not been determined.
Objectives: The objectives of this study were to examine the relation of 25(OH)D and PTH concentrations with whole-body insulin sensitivity and to determine whether lower 25(OH)D concentrations in AAs compared with EAs contribute to the lower insulin sensitivity of AAs relative to that of EAs.
Design: This was a cross-sectional study of 25 AA and 25 EA women. We determined the whole-body insulin sensitivity index (SI) with an intravenous glucose tolerance test and minimal modeling. Percentage body fat was determined with dual-energy X-ray absorptiometry, and intraabdominal adipose tissue (IAAT) was determined with computed tomography.
Results: Multiple linear regression analysis indicated that 25(OH)D and PTH concentrations were independent determinants of SI [standardized ? = 0.24 (P = 0.04) and −0.36 (P = 0.002), respectively] after adjustment for age, race, and IAAT. The mean ethnic difference in SI decreased from 2.70 [? 10−4 ? min−1/(?IU/mL)] after adjustment for IAAT and percentage body fat to 1.80 [? 10−4 ? min−1/(?IU/mL)] after further adjustment for 25(OH)D and PTH concentrations.
Conclusions: 25(OH)D and PTH concentrations were independently associated with whole-body insulin sensitivity in a cohort of healthy women, which suggested that these variables may influence insulin sensitivity through independent mechanisms. Furthermore, ethnic differences in 25(OH)D concentrations may contribute to ethnic differences in insulin sensitivity.

Source: Am J Clin Nutr December 2010 vol. 92 no. 6 1344-1349

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