Elevated blood pressure (BP) is a leading preventable cause of morbidity and mortality and an established independent risk factor for CVD and stroke. Fruit and vegetable-rich diets have been shown to reduce systolic blood pressure (SBP) in hypertensive subjects(Reference Joshipura, Hu and Manson1, Reference Sacks, Svetkey and Vollmer2). Green leafy vegetables conferred the strongest protection(Reference Joshipura, Hu and Manson1). These contain high concentrations of nitrate that can act as a substrate for the endogenous formation of the potent vasodilator nitric oxide after consumption(Reference Lundberg and Govoni3). Beetroot juice (BJ) is also rich in nitrate and has been shown to lower SBP by 10 mmHg in normotensive individuals when given as a 500 ml dose(Reference Webb, Patel and Loukogeorgakis4).
The present study investigated the dose-response effects of BJ on 24 h ambulatory blood pressure (ABP). Twenty-five normotensive volunteers (18 males and 7 females), aged 18–64 years, consumed 3 doses of BJ (100, 250 and 500 ml) and a water/no BJ control in a single-blind, randomized and controlled crossover study. Low-nitrate mineral water was used to match the volume in all drinks to 500 ml. ABP was determined every 15 min for 1 h pre- and 4 h post-drink consumption, every 30 min for a further 9 h and hourly overnight. Urine was collected at 0, 2, 4, 6 and 24 h after BJ consumption. The subjects followed a low-nitrate diet for 48 h and consumed standardised low-nitrate meals the night before and during the study day.
SBP was significantly reduced 2–3 h post ingestion by 6.73, 6.69 and 9.82 mmHg for 100, 250 and 500 ml BJ, respectively. Incremental area under the curve (IAUC) for SBP and diastolic BP (DBP) were significantly lower 0–240 min post ingestion (P<0.001) after all BJ doses with SBP remaining lower up to 780 min (P<0.001). Urinary nitrate/nitrite was significantly higher than no BJ for all doses (P<0.001) and remained significantly raised up to 24 h post consumption of 500 ml BJ (P=0.004). Urinary nitrate/nitrite IAUC was significantly and negatively correlated with IAUC for SBP and DBP (r 2=−0.331, P=0.001 and r 2=−0.240, P=0.017, respectively). Urine antioxidant potential significantly increased after 500 ml BJ at 240 min post ingestion.
Overall, the study showed that BJ ingestion significantly, and in a near dose-dependent manner, lowered BP and increased urine nitrate/nitrite levels in normotensive subjects. These findings support the existing evidence for a beneficial effect of nitrate-rich BJ in lowering BP, which may contribute to the cardioprotective effects of vegetable-rich diets.
