title: On the role of vitamin D binding globulin in glucose homeostasis: results from the San Luis Valley Diabetes Study.
abstract: Several studies have reported association between noninsulin-dependent diabetes mellitus and GC, the vitamin D binding protein of human plasma, with the GC 1 allele in significant excess among diabetics. Additionally, there is a considerable body of animal data suggesting that vitamin D has a significant impact on insulin secretion. Examination of the insulin levels in Dogrib Indians showed that the lowest levels of fasting insulin were associated with the GC IF-IF genotype. The present study examined levels of glucose, C-peptide, and insulin at fasting and 1 hr and 2 hr following a 75 g oral glucose challenge, in a population of Hispanic-Americans and Anglos in the San Luis Valley of southern Colorado. The sample comprised a total of 468 individuals with normal glucose tolerance. Of these, 289 were Anglos and 179 were Hispanic-Americans. An analysis of covariance was performed to determine the effect of the GC genotypes on mean levels of the primary variables--glucose, C-peptide, and insulin--and a secondary variable--insulinogenic index adjusting for the covariates age, body mass index (BMI), gender, and ethnicity. The analyses revealed that there is a significant difference in mean levels of glucose at fasting (F value = 2.46; P = 0.033) among the GC genotypes in the sample. Additionally, the differences in mean levels of 1 hr postprandial glucose among the GC genotypes although not significant at a 5% level, were significant at the 10% level. No other significant phenotypic effects were observed. These analyses are not in concordance with the results of an earlier study, where lower fasting insulin was associated with the GC 1F-1F genotype.
authors.affiliation: Human Genetics Division, Graduate School of Public Health, University of Pittsburgh, PA 15261.
authors.forename: S
authors.initials: S
authors.lastname: Iyengar
authors.forename: R F
authors.initials: RF
authors.lastname: Hamman
authors.forename: J A
authors.initials: JA
authors.lastname: Marshall
authors.forename: P P
authors.initials: PP
authors.lastname: Majumder
authors.forename: R E
authors.initials: RE
authors.lastname: Ferrell
mesh_terms: D001786:Blood Glucose / Q000235:genetics / Q000378:metabolism*; D002096:C-Peptide / Q000097:blood / Q000235:genetics; D016022:Case-Control Studies; D003120:Colorado / Q000453:epidemiology / Q000208:ethnology; D003924:Diabetes Mellitus, Type 2 / Q000453:epidemiology / Q000208:ethnology / Q000235:genetics*; D005260:Female; D005951:Glucose Tolerance Test; D006630:Hispanic or Latino / Q000235:genetics; D006706:Homeostasis; D006801:Humans; D007328:Insulin / Q000097:blood / Q000235:genetics; D008297:Male; D014809:Vitamin D-Binding Protein / Q000235:genetics*; D044465:White People / Q000235:genetics
chemical_list: D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin; D014809:Vitamin D-Binding Protein