Effects of Dietary Nitrate Supplements on Morning Blood Pressure Surge and Sympathetic Neural Control during Orthostasis in Post‐menopausal Women

Abstract

Post‐menopausal women are at greater risk for cardiovascular disease compared with age‐matched men. An exaggerated morning blood pressure surge (MBPS) in post‐menopausal women is well established as an independent risk factor for cardiovascular events. Dietary nitrate supplements such as nitrate‐rich beetroot juice (BRJ) may reduce blood pressure (BP), but no study has investigated the chronic effects of BRJ on MBPS and sympathetic neural control during orthostasis in post‐menopausal women. We hypothesized that dietary nitrate supplements would decrease MBPS and muscle sympathetic nerve activity (MSNA, microneurography) in post‐menopausal women.We performed a double‐blind, placebo‐controlled, cross‐over trial and randomly assigned healthy women [n=14, 64±3 (SD) yr] to either dietary nitrate supplements (140 ml of BRJ; 800 mg nitrate/day) or placebo (140 ml of nitrate‐depleted BRJ daily) for 2 weeks each with ≥2 weeks of washout. Twenty‐four‐hour ambulatory BP monitoring was performed and MBPS was calculated as the morning systolic BP (SBP; averaged for 2 h after wake‐up) minus the lowest nocturnal SBP before and after 2‐week BRJ or placebo intervention. BP, heart rate, and MSNA were measured during 3‐min supine rest and 5‐min 60° head‐up tilt (HUT). Cardiac output (Qc; C2H2 rebreathing) and total peripheral resistance (TPR=mean BP/Qc × 80) were also measured.MBPS decreased after BRJ intervention (Figure A; p=0.043). BRJ did not change hemodynamics or MSNA during supine rest (Figure B‐E; all, p>0.05). However, upright TPR was reduced (Figure C; p=0.007), while Qc trended greater (Figure B; p=0.072) after BRJ intervention. During HUT, MSNA burst frequency (53±15 pre vs. 48±10 bursts/min post, p=0.508 for posture × intervention interaction) and burst incidence (70±17 vs. 63±15 bursts/100 heart beats, p=0.199 for interaction) were similar, but mean burst area (Figure D; p=0.010) and total activity (Figure E; p=0.015) were lower after BRJ intervention. Placebo had no significant impact on hemodynamics and MSNA in the supine position or during HUT in post‐menopausal women (all, p<0.05).Collectively, dietary nitrate supplements decrease morning surge in BP and upright MSNA and vasoconstriction in post‐menopausal women. Whether reductions in sympathetic activation and peripheral vasoconstriction during orthostasis contribute to the reduced MBPS in these women remains to be determined.