Renal excretion of ascorbic acid: effect of age and sex.

To determine if the lower plasma ascorbic acid concentrations observed in males compared to females, and in the elderly in general, might be due to differences in renal clearances of ascorbic acid, tubular maximum reabsorptions (TmAA) and renal thresholds for ascorbic acid were determined on older (10 male, 10 female, aged 70-86 years) and younger (3 male, 5 female, aged 26-59 years) subjects. The mean TmAA for men was 1.54 +/- 0.29 and for women 1.39 +/- 0.33 mg/minute/100 mL glomerular filtration rate (p > 0.05). The mean renal threshold for men was 1.51 +/- 0.25 and for women 1.26 +/- 0.16 mg/dL (p < 0.02). Neither was affected by age. If differences in TmAA and renal threshold were to explain the lower plasma ascorbic acid concentrations observed in males, both values should have been lower than in females. The ability of women to maintain higher plasma ascorbic acid concentrations than men, and young higher than elderly, cannot be explained by differences in the renal handling of ascorbic acid.