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ACUTE DIETARY NITRATE SUPPLEMENTATION AND COLD PRESSOR TEST CARDIOVASCULAR RESPONSES IN YOUNG WOMEN

Abstract

BACKGROUND: Research specific to acute nutritional interventions that alter cardiovascular responses to stress in young women, is lacking. Beet root juice (BRJ) is highly concentrated with dietary nitrate which is a precursor to the compound nitric oxide (NO). NO is a potent vasodilator and has vascular health implications. The purpose of this study was to investigate the influence of acute BRJ supplementation on cardiovascular responses to a cold pressor test (CPT) in young women. METHODS: 17 (aged 18-23) women completed this placebo-controlled, counter-balanced, crossover protocol. Participants completed 3 laboratory visits (familiarization & 2 experimental). Experimental visits differed in the BRJ formula; whereby the placebo had nitrate removed by the manufacturer. Heart rate (HR), blood pressure (MAP = 1/3 SBP + 2/3 DBP), and rate pressure product [RPP = (HR⸱SBP)⸱0.01] were monitored immediately prior (pre), after (post), and during a 4-minute recovery window following a CPT. A mixed-model, linear regression with fixed factors of time (post, 1-min, 2-min, 3-min, 4-min) and treatment (placebo vs. experimental) were used to explore mean differences in dependent variables (MAP, HR, & RPP). Additionally, pre-measures of HR, MAP, and RPP were used as covariates to account for daily variation. Sidak adjustments were implemented if pairwise comparisons were warranted (α ≤ 0.05). RESULTS: Regression results revealed no interaction (all p > 0.26) nor main effect of treatment (all p > 0.40) for HR, MAP, or RPP. However, as expected, there was a main effect of time (all p < 0.001); whereby minute 0 was higher than minutes 1, 2, 3, and 4 during the recovery window for HR (adjusted mean ± SE; 0-min = 84 ± 1.4 bpm, 1-min = 74 ± 1.4 bpm, 2-min = 75 ± 1.4 bpm, 3-min = 76 ± 1.4 bpm, 4-min = 76 ± 1.4 bpm) and RPP (adjusted mean ± SE; 0-min = 116 ± 2.0 au, 1-min = 87 ± 2.0 au, 2-min = 83 ± 2.0 au, 3-min = 82 ± 2.0 bpm, 4-min = 83 ± 2 au) but no differences in other pairwise comparisons (p > 0.05). Furthermore, MAP (adjusted mean ± SE; 0-min = 107 ± 1.5 mmHg, 1-min = 88 ± 1.5 mmHg, 2-min = 82 ± 1.5 mmHg, 3-min = 80 ± 1.5 mmHg, 4-min = 80 ± 1.5 mmHg) for minutes 0 and 1 were higher than minutes 2, 3, & 4 (all p < 0.001) with no differences in other pairwise comparisons (p > 0.05). CONCLUSIONS: BRJ did not influence cardiovascular reactivity following a cold pressor test when compared to placebo.

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