Association of Directly-Measured Plasma Free 25(OH)D with Insulin Sensitivity and Secretion – the IRAS Family Study

Association of Directly-Measured Plasma Free 25(OH)D with Insulin Sensitivity and Secretion – the IRAS Family Study

J Clin Endocrinol Metab. 2017 05 10;:

Authors: Lee CC, Young KA, Norris JM, Rotter JI, Liu Y, Lorenzo C, Wagenknecht LE, Cole DE, Haffner SM, Chen YI, Hanley AJ

Abstract
Objectives: We aimed to compare the associations of directly measured plasma free 25-hydroxyvitamin D [25(OH)D] and total 25(OH)D concentrations with insulin sensitivity and beta-cell function in non-diabetic Hispanics and African-Americans. We hypothesized that directly measured free 25(OH)D would be more strongly associated with these measures of glucose homeostasis and that associations would differ by race.
Methods: We studied 1,189 non-diabetic participants in the Insulin Resistance Atherosclerosis Study (IRAS) Family Study, using data from baseline examinations in 2000–2002. Insulin sensitivity (SI), acute insulin response (AIR) and disposition index (DI) were determined from frequently sampled intravenous glucose tolerance tests. Plasma free and total 25(OH)D concentrations were measured by ELISA and radioimmunoassay, respectively.
Results: The median concentrations of plasma free 25(OH)D were 3.46 pg/ml for Hispanics and 2.17 pg/ml for African Americans (p<0.0001), while the median concentrations of plasma total 25(OH)D were 16 ng/ml for Hispanics and 10 ng/ml for African Americans (p<0.0001). Plasma free and total 25(OH)D were both positively associated with SI and DI in generalized estimating equations adjusted for demographic and lifestyle factors. After further adjustment with BMI, the associations were no longer statistically significant, except for a significant association between plasma free 25(OH)D and SI. There was no effect modification by ethnicity on any of the exposure-outcome associations.
Conclusions: Our data showed that plasma free 25(OH)D had a slightly stronger association with SI compared to plasma total 25(OH)D, although the difference was modest and there were no marked differences in the associations between Hispanics and African Americans.

PMID: 28609823 [PubMed - as supplied by publisher]

http://ift.tt/2s09yAj