Abstract
Many papers have been published on the relationship between vitamin C (VC) and disease risk. However, marked discrepancy exists in the relationship between VC and disease between the observational and intervention studies and the relationship is mostly positive in the former and negative in the latter. In this review article, we make a consideration underlying such discrepancy between VC and cardiovascular disease (CVD) risk.
Cohort and nested case-control studies have almost unequivocally shown that higher VC intake or higher plasma VC concentration is associated with decreased risk of various diseases including CVD. Of note, CVD risk exhibits a linear relationship with plasma VC level, while it exhibits a non-linear relationship with VC intake, which can be explained by the VC’s kinetic characteristics. Since intestinal absorption and renal tubular reabsorption of VC are tightly regulated, plasma VC concentration reaches a plateau with the increased VC intake.
In contrast, the negative results have been reported mostly in the intervention studies including the largest scale one, Physicians’ Health Study Ⅱ, in which more than 7,000 subjects in each group of the placebo and intervention were followed for 8 years. Such results could be explained by the following reasons: most participants are VC-sufficient and vitamin intervention is effective in the deficient subjects, but not in sufficient ones.
