Dietary Inorganic Nitrate Accelerates Cardiac Parasympathetic Recovery After Exercise in Older Women with...

Background/Objectives: Dietary inorganic nitrate (NO₃^-), primarily sourced from vegetables such as beetroot, has been shown to enhance nitric oxide (NO) bioavailability, with emerging evidence suggesting its potential to modulate autonomic function. However, the effects of NO₃^- supplementation on cardiac autonomic recovery post-exercise in hypertensive postmenopausal women remain poorly understood. Using data from a previously conducted randomised controlled trial, this study investigated the effects of acute (800 mg) and seven-day (400 mg/day) beetroot juice NO₃^- supplementation on ultra-short-term post-exercise cardiac parasympathetic recovery in hypertensive older women. Methods: In a triple-blind, placebo-controlled crossover design, fourteen postmenopausal women (59 ± 4 y) with hypertension completed two intervention arms (NO₃^- and placebo). Ultra-short-term heart rate variability (HRV) indices (SDNN, RMSSD, HF) were assessed across 5 min post-exercise recovery using 60 s windows. Plasma NO₂^- and NO₃^- concentrations were measured via chemiluminescence. Results: Both acute and seven-day NO₃^- supplementation significantly increased plasma NO₂^- and NO₃^- concentrations compared to placebo (p < 0.001). Cardiac vagal recovery, assessed via SDNN and RMSSD, was significantly enhanced in both conditions, with greater and more sustained improvements observed after the seven-day protocol. HF power was significantly higher, but only after seven-day supplementation (p = 0.009). Conclusions: Inorganic NO₃^- supplementation enhances post-exercise cardiac parasympathetic reactivation in hypertensive postmenopausal women. Notably, the seven-day intake (400 mg/day) protocol elicited superior autonomic benefits compared to an acute high dose. These findings highlight the potential of NO₃^- as a non-pharmacological strategy for improving cardiovascular autonomic recovery in high-risk populations.