The effect of pharmacological supplementation with vitamin C on low-density lipoprotein oxidation

Vitamin C (ascorbic acid) is a powerful antioxidant but there is limited information on its ability to prevent LDL oxidation and its interaction with other natural antioxidants in vivo. We assessed the effect of 4 weeks pharmacological supplementation with vitamin C 1 g day(-1) on copper induced LDL oxidation and lipid peroxidation.

Blood samples were obtained at baseline and at the end of 4 weeks supplementation from 11 healthy non-smokers and also from nine control subjects. Plasma lipid peroxides were measured as malondialdehyde (MDA) by h.p.l.c. The relationship between vitamin C and two other important antioxidants, vitamin E and glutathione, was also studied.

There was no difference in baseline values between the two groups and the oxidizability of LDL, assessed as the lag phase of conjugated dienes production and the formation of thiobarbituric acid reactive substances (TBARS), remained unchanged after 4 weeks. In the vitamin C supplemented group only, there was a 2.2-fold increase in plasma ascorbic acid level and a 28% increase in red cell reduced glutathione (GSH) (P<0.001). Vitamin E, measured as alpha-tocopherol, in red cells increased significantly (P<0.02) and plasma MDA was reduced (P<0.01).

Vitamin C did not alter LDL oxidation but it may have a protective role against lipid peroxidation as shown by decreased plasma MDA levels and enhanced vitamin E and GSH status.