Short-term and long-term vitamin C supplementation in humans dose-dependently increases the resistance of plasma to ex vivo lipid peroxidation.

To assess the effects of short-term and long-term vitamin C supplementation in humans on plasma antioxidant status and resistance to oxidative stress, plasma was obtained from 20 individuals before and 2h after oral administration of 2g of vitamin C, or from eight subjects enrolled in a vitamin C depletion-repletion study using increasing daily doses of vitamin C from 30 to 2500 mg. Plasma concentrations of ascorbate, but not other physiological antioxidants, increased significantly after short-term supplementation, and increased progressively in the long-term study with increasing vitamin C doses of up to 1000 mg/day. Upon incubation of plasma with a free radical initiator, ascorbate concentrations were positively correlated with the lag phase preceding detectable lipid peroxidation. We conclude that vitamin C supplementation in humans dose-dependently increases plasma ascorbate concentrations and, thus, the resistance of plasma to lipid peroxidation ex vivo. Plasma and body saturation with vitamin C in humans appears desirable to maximize antioxidant protection and lower risk of oxidative damage.