Beetroot Supplementation Lowers Blood Pressure, But Does Not Improve Exercise Efficiency In Female Masters Swimmers

Abstract

Beetroot supplements are high in dietary nitrate, which increases nitric oxide (NO) in the blood circulation. While NO can lower blood pressure and reduce the oxygen cost of exercise, this has mainly been studied in male athletes. Less is known about the effects of BRS in female athletes, especially swimmers. PURPOSE: To determine if acute beetroot supplementation (BRS) lowers blood pressure (BP) and improves exercise efficiency in female masters swimmers during treadmill exercise. METHODS: 11 swimmers (57.8±10.5 y) underwent 2 randomized, double-blinded trials and ingested beetroot supplement (BE) or placebo (PL). BP, heart rate (HR), and NO response, determined indirectly via changes in salivary nitrite (NO2-), was measured pre-ingestion (Base), pre-exercise (Pre), and 5 min post-exercise (Post). Oxygen consumption (VO2), HR, and rating of perceived exertion (RPE) were measured during the modified Balke test until HR reached 85% of age-predicted maximum. Changes in salivary NO2- were determined using NO2- detection strips and quantified as percentage of reference standard. 2-way repeated measures ANOVA was used to determine differences in BP, HR and salivary NO2-. Peak VO2, treadmill time, and peak RPE were analyzed by 2-tailed t-tests. RESULTS: Salivary NO2- increased from Base to Post in BE compared to PL (32.5 ± 7.0 vs 2.7 ± 3.9%, p=0.001). No treatment differences existed for peak VO2 (BE: 29.3 ± 2.0 vs PL: 29.7 ± 2.7 ml·kg-1·min-1, p=0.31), treadmill time (BE: 15.5 ± 1.9 vs PL: 15.4 ± 1.8 min, p=0.92), or peak RPE (BE: 6.2 ± 0.5 vs PL: 6.5 ± 0.5, p=0.26). Diastolic BP was significantly lower in BE vs PL, respectively (Base: 74.6 ± 1.7 vs 73.2 ± 2.3, Pre: 73.6 ± 1.8 vs 74.5 ± 2.1, Post: 74.5 ± 1.7 vs 76.1 ± 2.2 mmHg, p=0.03, treatment x time), while systolic BP changes trended towards significance in BE vs PL (Base: 116.6 ± 1.5 vs 115.5 ± 1.6, Pre: 115.0 ± 1.7 vs 116.0 ± 1.7, Post: 116.5 ± 1.4 vs. 118.3 ± 1.5 mmHg, p=0.053). HR at Base, Pre, and Post was not different in BE vs PL (62.0 ± 2.4, 63.2 ± 2.5, and 72.6 ± 3.2 vs 63.6 ± 2.1, 65.4 ± 2.2, and 74.6 ± 2.4 bpm, p=0.86). CONCLUSIONS: Acute BRS lowers diastolic BP, but does not improve exercise efficiency in this group of trained, normotensive female masters swimmers. More research is needed in other female masters athlete groups such as runners and cyclists, and in female athletes with hypertension.