title: Human skeletal muscle ascorbate is highly responsive to changes in vitamin C intake and plasma concentrations.
abstract: BACKGROUND
  Vitamin C (ascorbate) is likely to be essential for skeletal muscle structure and function via its role as an enzyme cofactor for collagen and carnitine biosynthesis. Vitamin C may also protect these metabolically active cells from oxidative stress.
  
  
  OBJECTIVE
  We investigated the bioavailability of vitamin C to human skeletal muscle in relation to dietary intake and plasma concentrations and compared this relation with ascorbate uptake by leukocytes.
  
  
  METHODS
  Thirty-six nonsmoking men were randomly assigned to receive 6 wk of 0.5 or 2 kiwifruit/d, an outstanding dietary source of vitamin C. Fasting blood samples were drawn weekly, and 24-h urine and leukocyte samples were collected before intervention, after intervention, and after washout. Needle biopsies of skeletal muscle (vastus lateralis) were carried out before and after intervention.
  
  
  RESULTS
  Baseline vastus lateralis ascorbate concentrations were ~16 nmol/g tissue. After intervention with 0.5 or 2 kiwifruit/d, these concentrations increased ~3.5-fold to 53 and 61 nmol/g, respectively. There was no significant difference between the responses of the 2 groups. Mononuclear cell and neutrophil ascorbate concentrations increased only ~1.5- and ~2-fold, respectively. Muscle ascorbate concentrations were highly correlated (P < 0.001) with dietary intake (R = 0.61) and plasma concentrations (R = 0.75) in the range from 5 to 80 μmol/L.
  
  
  CONCLUSIONS
  Human skeletal muscle is highly responsive to vitamin C intake and plasma concentrations and exhibits a greater relative uptake of ascorbate than leukocytes. Thus, muscle appears to comprise a relatively labile pool of ascorbate and is likely to be prone to ascorbate depletion with inadequate dietary intake. This trial was registered at the Australian New Zealand Clinical Trials Registry (www.anzctr.org.au) as ACTRN12611000162910.
authors: Centre for Free Radical Research, Department of Pathology, University of Otago, Christchurch, Christchurch, New Zealand. anitra.carr@otago.ac.nz
authors: Anitra C
authors: AC
authors: Carr
authors: Stephanie M
authors: SM
authors: Bozonet
authors: Juliet M
authors: JM
authors: Pullar
authors: Jeremy W
authors: JW
authors: Simcock
authors: Margreet Cm
authors: MC
authors: Vissers
mesh_terms: D029042:Actinidia / Q000737:chemistry; D000293:Adolescent; D000328:Adult; D001205:Ascorbic Acid / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D001682:Biological Availability; D004032:Diet; D005638:Fruit / Q000737:chemistry; D006801:Humans; D007963:Leukocytes, Mononuclear / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009504:Neutrophils / Q000378:metabolism; D014815:Vitamins / Q000008:administration & dosage / Q000097:blood / Q000378:metabolism* / Q000493:pharmacokinetics; D055815:Young Adult
chemical_list: D014815:Vitamins; D001205:Ascorbic Acid