serum vitamin d concentration does not predict insulin action or secretion in european subjects with the metabolic syndrome objective to investigate the relation between serum concentration of 25hydroxyvitamin d 25ohd and insulin action and secretionresearch design and methods in a crosssectional study of 446 paneuropean subjects with the metabolic syndrome insulin action and secretion were assessed by homeostasis model assessment homa indexes and intravenous glucose tolerance test to calculate acute insulin response insulin sensitivity and disposition index serum 25ohd was measured by highperformance liquid chromatographymass spectrometryresults the 25ohd3 concentration was 571 260 nmoll mean sd and only 20 of the subjects had 25ohd3 levels or 75 nmoll in multiple linear analyses 25ohd3 concentrations were not associated with parameters of insulin action or secretion after adjustment for bmi and other covariatesconclusions in a large sample of subjects with the metabolic syndrome serum concentrations of 25ohd3 did not predict insulin action or secretion clear evidence that d vitamin status directly influences insulin secretion or action is still lacking