Does supplemental vitamin C increase cardiovascular disease risk in women with diabetes?

Background Vitamin C acts as a potent antioxidant; however, it can also be a prooxidant and glycate protein under certain circumstances in vitro. These observations led us to hypothesize that a high intake of vitamin C in diabetic persons might promote atherosclerosis. Objective The objective was to examine the relation between vitamin C intake and mortality from cardiovascular disease. Design We studied the relation between vitamin C intake and mortality from total cardiovascular disease (n = 281), coronary artery disease (n = 175), and stroke (n = 57) in 1923 postmenopausal women who reported being diabetic at baseline. Diet was assessed with a food-frequency questionnaire at baseline, and subjects initially free of coronary artery disease were prospectively followed for 15 y. Results After adjustment for cardiovascular disease risk factors, type of diabetes medication used, duration of diabetes, and intakes of folate, vitamin E, and β-carotene, the adjusted relative risks of total cardiovascular disease mortality were 1.0, 0.97, 1.11, 1.47, and 1.84 (P for trend < 0.01) across quintiles of total vitamin C intake from food and supplements. Adjusted relative risks of coronary artery disease were 1.0, 0.81, 0.99, 1.26, and 1.91 (P for trend = 0.01) and of stroke were 1.0, 0.52, 1.23, 2.22, and 2.57 (P for trend < 0.01). When dietary and supplemental vitamin C were analyzed separately, only supplemental vitamin C showed a positive association with mortality endpoints. Vitamin C intake was unrelated to mortality from cardiovascular disease in the nondiabetic subjects at baseline. Conclusion A high vitamin C intake from supplements is associated with an increased risk of cardiovascular disease mortality in postmenopausal women with diabetes.