Figure 7. Carnitine supplementation improves glucose homeostasis in insulin resistant humans.

Older aged human subjects (n=14) with modestly elevated fasting blood glucose levels received supplemental L-carnitine (2 g/day) for 6 months. Fasting serum samples were collected pre- and post-intervention for measurement of free carnitine (panel A), acetylcarnitine (panel B), HOMA (panel C), glucose (panel D) and insulin (panel E). Tissue homogenates prepared from vastus lateralis biopsies were used to measure PDH activity with 5 mM [1-¹⁴C]pyruvate (panel F). Substrate switching was determined by measuring oxidation of 50μM [1-¹⁴C]palmitate (panel G) or 5 mM [2-¹⁴C]pyruvate (panel H) to ¹⁴CO₂ in the absence or presence of the unlabeled competing substrate (5 mM pyruvate or 100μM palmitate, respectively). Results were stratified according to HOMA at enrollment, using a cut off of 1.5; n=8 below and n=6 above. * Effect of carnitine supplementation analyzed by 1-tailed paired Student's t-test (p<0.05).