Dietary nitrate supplementation has been shown to lower blood pressure (BP) particularly in short-term clinical trials. Whether these effects are sustained in the long-term remains to be established. The objective was to conduct a meta-analysis of randomized controlled trials that examined whether dietary nitrate supplementation for more than 1 week has beneficial effects on SBP and DBP.Methods:
Electronic databases were searched from inception until May 2016. Specific inclusion criteria were duration at least 1 week, report of effects on SBP or DBP or both and comparison of inorganic nitrate or beetroot juice supplementation with placebo control groups. Random-effects models were used to calculate the pooled BP effect sizes.Results:
Thirteen trials met eligibility criteria. The trials included a total of 325 participants with seven to 65 participants per study. The duration of each intervention ranged from 1 to 6 weeks. Ten trials assessed BP in resting clinic conditions, whereas 24-h ambulatory and daily home monitorings were used in six and three trials, respectively. Overall, dietary nitrate was associated with a significant decline in SBP [−4.1 mmHg (95% confidence interval: −6.1, −2.2); P < 0.001] and DBP [−2.0 mmHg (95% confidence interval: −3.0, −0.9); P < 0.001]. However, the effect was only significant when measured in resting clinical settings as no significant changes in BP were observed using 24-h ambulatory and daily home BP monitorings.Conclusion:
Positive effects of medium-term dietary nitrate supplementation on BP were only observed in clinical settings, which were not corroborated by more accurate methods such as 24-h ambulatory and daily home monitorings.