Effects of Dietary Nitrate Supplementation on Blood Pressure Reduction, A Systematic Review and Meta-Analysis
Creators: name: Shi, Shuai
Publisher: name: The University of North Carolina at Chapel Hill University Libraries
Year: 2020

description: AbstractBackgroundHigh blood pressure is the greatest risk factor for diseases such as hypertension, stroke, and cardiovascular disease.  Blood pressure control has become a global public health priority. Nitric oxide (NO), which can be converted from nitrate, has been reported to reduce blood pressure. Clinical trials have been conducted to test the effect of dietary intake rich in nitrate on reduction of blood pressure and the results have been inconsistent. We aimed to conduct a meta-analysis of randomized clinical trials to evaluate the impact of dietary nitrate on blood pressure (BP) reduction. MethodsPubmed, EMBASE, and Web of Science were systematically searched from inception until July 2018. We included the randomized clinical trials that examined the effect of dietary nitrate supplementation like beetroot supplementation in reducing systolic blood pressure (SBP) and diastolic blood pressure (DBP) compared to taking placebo or low nitrate supplementation. A random-effects meta-analysis was conducted to evaluate the intervention of nitrate diet on the control of BP.ResultsA total of 41 trials including 733 participants (with 5 to 65 participants per study) were eligible. The duration of each intervention ranged from 3 hours to 12 weeks with the median value of 3 days (25%-75% quartile range equal to 1-7 days).  21 out of 41 studies showed that dietary nitrate was associated with a significant decline in SBP compared to placebo, while only 12 out of the 21 above studies indicated that dietary nitrate was also associated with a significant DBP reduction. There were 3 studies where dietary nitrate significantly reduced in DBP but not SBP. Overall, blood pressure (BP) reductions were -3.12 mm Hg (95% CI, -4.59 to -1.54) for systolic and -1.43 mm Hg (95% CI, -2.55 to -0.30) for diastolic. The greater effect size on BP reduction was found among the groups with the interventions of beetroot juice and nitrate-depleted placebo (MD in SBP for beetroot juice=-4.68 mmHg, 95% CI: -6.57 to -2.01, MD in DBP for beetroot juice=-2.35 mmHg, 95% CI: -3.86 to -0.84, MD in SBP for nitrate-depleted placebo=-4.40 mmHg, 95% CI: -6.79 to -2.01, and MD in DBP for nitrate-depleted placebo=-2.10 mmHg, 95% CI: -3.85 to -0.35). The higher impact of beetroot and inorganic nitrate supplementation on BP reduction found in older subjects was mostly associated with the structural changes in their arteries and especially with large artery stiffness. Our meta-regression analysis also demonstrated a significant negative relationship between age and the treatment effect on DBP after beetroot and inorganic nitrate consumption (slope=-0.0696; p=0.031).ConclusionOverall, dietary nitrate showed significant effect in reducing SBP, while that in reducing DBP is less consistent. This study provided insight to potential complementary therapies for acute blood pressure lowering effect in populations, particularly when internal source of NO suffers from dysfunction.  Dietary nitrate is an essential supplement for the prevention and treatment of hypertension. Public health leaders should implement effective interventions that incorporate individual behavior changes to increase intake of nitrate diet and environmental changes to encourage and promote greater access to healthier food.