Pharmacokinetics of oral vitamin C
STEPHEN HICKEY, HILARY J. ROBERTS, & NICHOLAS J. MILLER
"Figure 1 shows the response of the female subject to single 5 g doses of
liposomal and
standard formulation vitamin C; both produced similar response curves. These results are
comparable in form and magnitude to those expected for oral vitamin C in previously
depleted subjects. However, peak values exceeded 220 mM L which has been reported as
the maximum value attainable with repeated oral doses of 3 g six times daily [8]. The
subjects were experienced users of high-dose vitamin C and neither suffered any
gastrointestinal effects at this dose level.5 "
Increasing the dose of
liposomal vitamin C to 20g gave a broader response, with
a delayed maximum, as shown in Figure 2. In this graph, the 20g
liposomal dose is
compared with a 5g standard dose (male subject). With a 20g intake, the peak plasma
level was delayed and the response was broader, indicating a greater absorption of
vitamin C. The 5g data set shows a marked outlier (peak): this is attributed to the fact
that one of the (5g) blood samples was difficult to extract, with inflammation at the
puncture site, providing only a small sample. The subject experienced no bowel
tolerance effects at either of these intakes.
Figure 3 shows plasma levels following a 36g dose of
liposomal vitamin C, for
both subjects. This resulted in peak plasma levels, in the region of 400 µM/L. A 95%
interfractile range (34-114), which contains 95% of the distribution with a mean of 74
corresponds to a calculated standard deviation of 17.4. We note that, under these
conditions, an outlier measurement of 400 µM/L would correspond to a deviation of
10.3 σ with a theoretical p value of 1.6x10 -13 (i.e. P<0.0000000000001). With this high
dose, both subjects exceeded their bowel tolerance, leading to diarrhoea. This
intolerance presumably arose from the high intake of phospholipid, without food
buffering, in fasting individuals. However, our observations using hourly doses suggest
that daily intakes of this magnitude are tolerable without bowel effects, as long as the
dose is spread throughout the day.
