Plasma vitamin C affects glucose homeostasis in healthy subjects and in non-insulin-dependent diabetics.
In aged healthy (n = 10) and non-insulin-dependent (type II) diabetic (n = 10) subjects matched for age [67.3 +/- 0.5 vs. 68.0 +/- 0.4 yr, P = not significant (NS)], body mass index (25.7 +/- 0.7 vs. 26.0 +/- 0.2 kg/m2, P = NS), gender ratio [6 males (M)/4 females (F) vs. 5 M/5 F], and mean arterial blood pressure (104 +/- 6 vs. 105 +/- 9 mmHg, P = NS), we determined the changes in insulin secretion and action after vitamin C infusion and the relative increase in plasma vitamin C levels. At the highest vitamin C infusion rate (0.9 mmol/min) the increase in plasma vitamin C levels did not affect B cell response to glucose, but it improved Conard's K values and whole body glucose disposal in healthy subjects and in diabetic patients. In both groups of subjects vitamin C-mediated increase in insulin action was mainly due to an improvement in nonoxidative glucose metabolism. After fasting, plasma vitamin C levels correlated with basal whole body glucose disposal (r = -0.44, P < 0.05; n = 20). After vitamin C infusion, percent change in plasma vitamin C level correlated with the percent decline in membrane microviscosity (r = 0.53, P < 0.01; n = 20) and increase in whole body glucose disposal (r = 0.63, P < 0.003; n = 20). In conclusion, plasma vitamin C levels seem to play a role in the modulation of insulin action in aged healthy and diabetic subjects.
Paolisso
G
G
Department of Geriatric Medicine and Metabolic Diseases, Medical School, II University of Naples, Italy.
D'Amore
A
A
Balbi
V
V
Volpe
C
C
Galzerano
D
D
Giugliano
D
D
Sgambato
S
S
Varricchio
M
M
D'Onofrio
F
F
D000368:Aged; D001205:Ascorbic Acid / Q000097:blood* / Q000494:pharmacology; D001786:Blood Glucose / Q000378:metabolism*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood*; D004305:Dose-Response Relationship, Drug; D004910:Erythrocyte Membrane / Q000502:physiology; D005260:Female; D015309:Glucose Clamp Technique; D005951:Glucose Tolerance Test; D006706:Homeostasis; D006801:Humans; D008297:Male; D012016:Reference Values; D014783:Viscosity
D001786:Blood Glucose; D001205:Ascorbic Acid