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.

Abstract

BACKGROUND\nVitamin 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.\n\n\nAIMS\nWe 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.\n\n\nMETHODS\nTen younger (age 18-40\xa0y) and ten older (age 55-70\xa0y) healthy participants were enrolled in a randomised double-blind crossover clinical trial. Participants ingested a solution of potassium nitrate (7\xa0mg/kg body weight) and/or vitamin C (20\xa0mg/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.\n\n\nRESULTS\nVitamin C supplementation reduced PWV significantly (vitamin C:\xa0-0.70\xa0±\xa00.31\xa0m/s; vitamin C placebo:\xa0+0.43\xa0±\xa00.30\xa0m/s; P\xa0=\xa00.007). There were significant interactions between age and vitamin C for systolic, diastolic, and mean arterial BP (P\xa0=\xa00.02, P\xa0=\xa00.03, P\xa0=\xa00.02, 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\xa0=\xa00.81; diastolic: P\xa0=\xa00.24; mean BP: P\xa0=\xa00.87) or vascular function (PORH: P\xa0=\xa00.05; PWV: P\xa0=\xa00.44) significantly in both younger and older participants. However, combined supplementation with nitrate and vitamin C reduced mean arterial BP (-2.6\xa0mmHg, P\xa0=\xa00.03) and decreased PWV in older participants (PWV:\xa0-2.0\xa0m/s, P\xa0=\xa00.02).\n\n\nCONCLUSIONS\nThe 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.\n\n\nCLINICAL TRIAL REGISTRATION\nCurrent Controlled Trials (ISRCTN98942199).