Effects of age and intake on vitamin C disposition in females

The pharmacokinetics of vitamin C following a 500 mg oral tablet dose were compared in a group of fourteen healthy young women whose age was 26.0 +/- 2.8 years (mean +/- s.d.), and in a group of fourteen healthy elderly women aged 68.1 +/- 2.6 years. The body composition of each subject was assessed using several anthropometric measurements in order to help explain any observed differences in the pharmacokinetic behavior of vitamin C. The vitamin C doses were characterized with the subjects in two states of vitamin C nutriture: a 'depleted' state which was achieved by 4-5 weeks on a vitamin C-restricted diet of less than 10 mg/d and a 'supplemented' state in which the subjects were given daily doses of 500 mg of vitamin C for 3 weeks. Plasma and urine samples were collected for 72 h following the dose of vitamin C from subjects in a 'depleted' state and for 24 h from subjects in a 'supplemented' state and analysed for their vitamin C content. None of the pharmacokinetic parameters measured differed significantly between the two age groups. In contrast, the vast majority of these parameters were significantly different in depleted and supplemented subjects. The peak times (tmax) were greater in the depleted state in both young and elderly groups whereas the peak concentrations (Cmax) were greater in the supplemented state. The absorption rate constant (Ka) was significantly larger in the supplemented state compared to the depleted state in the young group and the absorption half-life (t 1/2, Ka) was significantly greater in the depleted state in the young group only. The absorption lag time (tlag) did not differ with respect to age or nutritional status. The elimination half-life (t 1/2, Ke) was significantly longer in supplemented subjects. Although the apparent high volume of distribution (Vd) was not significantly different within each age group the Vd was significantly greater in the depleted state when the two age groups were combined. The clearance (CL), and the nonrenal clearance (CLNR) were significantly greater in the depleted state. The renal clearance (CLR) and the amounts of vitamin C excreted in the 0- to 12- and 12- to 24-h intervals were significantly larger in the supplemented state. The urinary excretion data also indicate that, in supplemented subjects, an average of about 40 percent of the administered dose is excreted as unchanged vitamin C in the first 12 h after dosing, with very little being excreted thereafter.