individuals, it prompted the suggestion that impaired intestinal
absorption may be an important causative factor in low blood
concentrations of vitamin C in the elderly.  However, other
studies, both cross-sectional and longitudinal, of apparently
healthy, well-nourished elderly populations in the United States
have not found evidence of a greater incidence of vitamin C
deficiency among the elderly compared to young adults and no
decrease in plasma ascorbate with advancing age (Garry et al.,
1982, 1987; Jacob et al., 1988). Measurement of plasma,
leukocyte, and urine ascorbate concentrations in a series of
studies in elderly and young men and women showed no differences
due to age (Blanchard, 1991a; Blanchard et al., 1989, 1990a,b).
These studies included pharmacokinetic measures related to
vitamin C absorption, depletion, repletion, and renal clearance.
Consistent with these findings, a later study that measured
maximal renal tubular reabsorption and excretion thresholds of
ascorbic acid in apparently health