The Effect of Dietary Nitrate and Vitamin C on Endothelial Function and Oxidative Stress Biomarkers

Abstract

Abstract Objectives Examine the effects of concentrated beetroot juice (CBJ) supplementation with and without vitamin C on markers of endothelial function (reactive hyperemia index (RHI) and blood biomarkers) and lipid profiles. Methods Subjects 50 to 70 years of age with low density lipoprotein (LDL) > 130 mg/dL and RHI ≤ 2 were enrolled in this randomized crossover double-blind study. Two 4-week interventions were separated by a 2-week washout. Subjects were assigned to daily CBJ (70 mls) with 1000 mg of vitamin C (NC) or CBJ with matched placebo (N), then switched to alternate treatment. At baseline and 4-weeks, RHI was measured using EndoPAT. Secondary outcomes included the sum of plasma NO metabolites (NO2 + NO3 = NOx), oxidized LDL (oxLDL), and serum lipids. Paired t-tests were used to compare differences between treatments. Results Eighteen of 23 subjects completed all study visits (7 male, 11 females). No significant treatment differences were observed in RHI change (N: 0.21 ± 0.46; NC: 0.20 ± 0.67; P > 0.05). NC subjects with baseline RHI of < 1.67 (mean = 1.23; n = 8) had greater improvements in RHI compared to subjects with RHI scores > 1.67 (mean = 1.75; n = 8; P = 0.02). Compared to N, NC resulted in a significant increase in plasma NOx (N: 94.2 ± 15.5 μmol/L; NC: 128.7 ± 29.1 μmol/L; P = 0.01). NC treatment reduced oxLDL/NOx ratio compared to N (N: −3.97 ± 2.8 U/L; NC: −4.29 ± 3.1 U/L; P = 0.02). NC elicited significant reductions in LDL (N: 2.2 ± 2; NC: −10.7 ± 23; P = 0.049), and triglycerides (N: 14.6 ± 43; NC: −43.7 ± 45; P = 0.03) with no change in serum high density lipoprotein. Conclusions NC appears effective at improving RHI in subjects with evidence of endothelial dysfunction. Four weeks of NC enriched the NO pool and promoted favorable changes in oxLDL/NOx ratio and blood lipids in subjects with hypercholesterolemia. These preliminary findings highlight a novel supplementation strategy that may reduce the progression of atherosclerotic disease and deserves further attention in studies using flow mediated dilation methods. Funding Sources Thornton Scholarship funds, College of Health Sciences, University of Kentucky.