Effect of vitamin C on plasma lipids

OBJECTIVE: To review the effects of vitamin C (ascorbic acid) on plasma lipid concentrations, and to address the proposed mechanisms through which vitamin C may potentially alter lipid concentrations. DATA SOURCE: A MEDLINE search was performed to identify pertinent English-language literature including studies, abstracts, and review articles. Key search terms were vitamin C, ascorbic acid, lipoproteins, lipids, and atherosclerosis. STUDY SELECTION AND DATA EXTRACTION: Studies examining the relationships between vitamin C and plasma lipid concentrations including animal, observational, and clinical trials were selected. Because there were no large randomized, controlled clinical trials, data were extracted from all clinical trials, regardless of design. Review articles discussing the effects of vitamin C on plasma lipid concentrations and the atherosclerotic process also were included. Pertinent information, as judged by the authors, was extracted for discussion. DATA SYNTHESIS: Evidence suggests an inverse relationship between vitamin C intake and the development of atherosclerosis, although the effect has not yet been proven in clinical trials. It has been postulated that this effect might be mediated not only through the antioxidant properties of vitamin C, but also through a plasma lipid-modifying effect. Data from animal and observational trials suggest that high vitamin C concentrations may correlate negatively with concentrations of total cholesterol, triglycerides, and low-density lipoproteins and positively with high-density lipoproteins. Other studies, however, have not confirmed these findings. Similarly, results from clinical trials have been widely variable and inconclusive. CONCLUSIONS: Analysis of the literature suggests an association between vitamin C and plasma lipid concentrations and a potential role in slowing the development of atherosclerosis. Significant variations and inadequacies in trial design, however, prohibit definitive conclusions. On the basis of these preliminary data, it appears that there is justification for additional well-designed trials to further evaluate the relationship between vitamin C and plasma lipid concentrations.