Effects of inorganic nitrate and vitamin C co-supplementation on blood pressure and vascular function in younger and older healthy adults: A randomised double-blind crossover trial

Background: Vitamin C and inorganic nitrate have been linked to enhanced nitric oxide (NO) production and reduced oxidative stress. Vitamin C may also enhance the conversion of nitrite into NO. Aims: We investigated the potential acute effects of vitamin C and inorganic nitrate co-supplementation on blood pressure (BP) and peripheral vascular function. The secondary aim was to investigate whether age modified the effects of vitamin C and inorganic nitrate on these vascular outcomes. Methods: Ten younger (age 18-40 y) and ten older (age 55-70 y) healthy participants were enrolled in a randomised double-blind crossover clinical trial. Participants ingested a solution of potassium nitrate (7 mg/kg body weight) and/or vitamin C (20 mg/kg body weight) or their placebos. Acute changes in resting BP and vascular function (post-occlusion reactive hyperemia [PORH], peripheral pulse wave velocity [PWV]) were monitored over a 3-h period. Results: Vitamin C supplementation reduced PWV significantly (vitamin C: -0.70 +/- 0.31 m/s; vitamin C placebo: +0.43 +/- 0.30 m/s: P = 0.007). There were significant interactions between age and vitamin C for systolic, diastolic, and mean arterial BP (P = 0.02, P = 0.03, P = 0.02, respectively), with systolic, diastolic and mean BP decreasing in older participants and diastolic BP increasing in younger participants following vitamin C administration. Nitrate supplementation did not influence BP (systolic: P = 0.81; diastolic: P = 0.24; mean BP: P = 0.87) or vascular function (PORH: P = 0.05; PWV: P = 0.44) significantly in both younger and older participants. However, combined supplementation with nitrate and vitamin C reduced mean arterial BP (-2.6 mmHg, P = 0.03) and decreased PWV in older participants (PWV: -2.0 m/s, P = 0.02). Conclusions: The co-administration of a single dose of inorganic nitrate and vitamin C lowered diastolic BP and improved PVW in older participants. Vitamin C supplementation improved PWV in both age groups but decreased systolic and mean BP in older participants only. (C) 2019 Elsevier Ltd and European Society for Clinical Nutrition and Metabolism. All rights reserved.