Seven-day dietary nitrate supplementation clinically significantly improves basal macrovascular function in postmenopausal women: a randomized, placebo-controlled, double-blind, crossover clinical trial

Introduction: Cardiovascular disease (CVD) is the leading cause of death in women, with increased risk following menopause. Dietary intake of beetroot juice and other plant-based nitrate-rich foods is a promising non-pharmacological strategy for increasing systemic nitric oxide and improving endothelial function in elderly populations. The purpose of this randomized, placebo-controlled, double-blind, crossover clinical trial was to determine the effects of short-term dietary nitrate (NO₃⁻) supplementation, in the form of beetroot juice, on resting macrovascular endothelial function and endothelial resistance to whole-arm ischemia–reperfusion (IR) injury in postmenopausal women at two distinct stages of menopause. Methods: Early-postmenopausal [1–6 years following their final menstrual period (FMP), n = 12] and late-postmenopausal (6+ years FMP, n = 12) women consumed nitrate-rich (400 mg NO₃⁻/70 mL) and nitrate-depleted beetroot juice (approximately 40 mg NO₃⁻/70 mL, placebo) daily for 7 days. Brachial artery flow-mediated dilation (FMD) was measured pre-supplementation (Day 0), and approximately 24 h after the last beetroot juice (BR) dose (Day 8, post-7-day BR). Consequently, FMD was measured immediately post-IR injury and 15 min later (recovery). Results: Results of the linear mixed-effects model revealed a significantly greater increase in resting FMD with 7 days of BR_nitrate compared to BR_placebo (mean difference of 2.21, 95% CI [0.082, 4.34], p = 0.042); however, neither treatment blunted the decline in post-IR injury FMD in either postmenopausal group. Our results suggest that 7-day BR_nitrate-mediated endothelial protection is lost within the 24-h period following the final dose of BR_nitrate. Conclusion: Our findings demonstrate that nitrate-mediated postmenopausal endothelial protection is dependent on the timing of supplementation in relation to IR injury and chronobiological variations in dietary nitrate metabolism. Clinical trial registration: https://classic.clinicaltrials.gov/ct2/show/NCT03644472