Chromium Effects on Insulin and Vascular Function in People at Risk for Diabetes

Impaired glucose tolerance (IGT), impaired fasting glucose (IFG), and insulin resistance (IR) are precursors to type II diabetes mellitus (DM) and its sequelae, and are cardiac risk factors in their own right. The worsening epidemic of DM in the US, along with the increasing prevalence of obesity, insulin resistance, and IGT, render the identification of promising interventions for these states a matter of some urgency. While lifestyle interventions based on dietary pattern and physical activity can delay or prevent the onset of diabetes, and reduce cardiovascular risk, adherence at the population level is severely limiting. Pharmacotherapy offers promise for diabetes prevention, but with associated high costs, unacceptability to many patients, and potential toxicity. In this context, the potential role of chromium (Cr), an insulin co-factor, in IGT is of great interest. Chromium use is widespread, but evidence of any therapeutic effect is limited. Proposed, therefore, is a randomized, double-blind, placebo controlled pilot trial conducted at the Yale Prevention Research Center, to investigate the effects of daily Cr for 6 months at two dose levels on serum measures of glucose tolerance, and on endothelial function, in adults with IGT, IFG, and IR. A modified crossover design will allow for paired and unpaired analyses including comparison of both 500 mcg and 1,000 mcg of Cr daily to placebo; comparison between 500 mcg and 1000 mcg of chromium; and evaluation of Cr washout time. The study is powered to detect a clinically meaningful effect of Cr supplementation at either dose on glucose control, and to compare the two doses for equivalence. The study will investigate effects of Cr on both measures of glucose tolerance (glucose, insulin, OGTT) and brachial artery endothelial function, thus combining serum measures with a physiologic test of Cr effects on the vasculature. The proposed study will generate much needed data regarding the efficacy of Cr in those at risk for type II diabetes and offers the promise of guiding practice, as well as directing future study. By contributing to knowledge related to potential diabetes prevention strategies, this study addresses one of the more pressing public health issues in the US today. Risk to human subjects in this study is a minor increment over minimal due to the administration of nitroglycerin as a control in BARS testing.