Purpose: Chromium enhances insulin signaling and insulin-mediated glucose uptake in cultured cells. We investigated the effect of chromium on glycogen synthesis and insulin signaling in humans.
Methods: Sixteen overweight men (BMI = 31.1 ± 3.0 kg·m−2) were randomly assigned to supplement with 600 μg·d−1 chromium+3 as picolinate (Cr; N = 8) or a placebo (Pl; N = 8). After 4 wk of supplementation, subjects performed a supramaximal bout of cycling exercise to deplete muscle glycogen, which was followed by high-glycemic carbohydrate feedings for the next 24 h. Muscle biopsies were obtained at rest, immediately after exercise, and 2 and 24 h after exercise.
Results: Elevations in glucose and insulin during recovery were not different, but the lactate response was significantly higher in Cr. There was a significant depletion in glycogen immediately after exercise, an increase at 2 h, and a further increase above rest at 24 h (P < 0.05). The rate of glycogen synthesis during the 2 h after exercise was not different between groups (Cr: 25.8 ± 8.0 and Pl: 17.1 ± 4.7 mmol·kg−1·h−1). Glycogen synthase activity was significantly increased immediately after exercise in both groups. Muscle phosphatidylinositol 3-kinase (PI 3-kinase) activity decreased immediately after exercise and increased at 2 h (P < 0.05), with a trend for a lower PI 3-kinase response in Cr (P = 0.08).
Conclusions: Chromium supplementation did not augment glycogen synthesis during recovery from high-intensity exercise and high-carbohydrate feeding, although there was a trend for lower PI 3-kinase activity.
1Human Performance Laboratory, Department of Kinesiology, University of Connecticut, Storrs, CT; 2Departments of Gastroenterelogy and Pathobiology, Lerner Research Institute, Cleveland Clinic, Cleveland, OH; and 3School of Exercise, Biomedical and Health Sciences, Edith Cowan University, Joondalup, AUSTRALIA
Address for correspondence: Jeff S. Volek, Ph.D., R.D., Department of Kinesiology, 2095 Hillside Road, Unit 1110, University of Connecticut, Storrs, CT 06269-1110; E-mail: email@example.com.
Submitted for publication March 2006.
Accepted for publication June 2006.