In aerobic respiration, the main form of cellular respiration used by humans, glucose, and oxygen is metabolized to release energy, with carbon dioxide and water as byproducts. Most of the fructose and galactose travel to the liver, where they can be converted to glucose. Glucose metabolism is frequently impaired in CKD.164, 165 In end-stage renal disease (ESRD), the most profound disturbance is insulin resistance due to a post-receptor defect in skeletal muscle.166, 167 Insulin resistance appears to be common in earlier stages of CKD, as well.87, 168, 169 Vitamin D may improve glucose metabolism by stimulating insulin secretion from pancreatic beta cells and by improving peripheral insulin sensitivity. Glucose metabolism in AKI again is affected both by unspecific mechanisms mediated by the acute disease state and specific effects of acute uremia. A major finding is insulin resistance. Plasma insulin concentrations are elevated, maximal insulin-stimulated glucose uptake by skeletal muscle is decreased and muscular glycogen synthesis is impaired.