Effect of inorganic nitrate supplementation on blood pressure in older adults: A systematic review and meta-analysis

Background: Previous clinical studies have shown controversial results regarding the effect of inorganic nitrate supplementation on blood pressure (BP) in older individuals. We performed this systematic review and metaanalysis to assess the effect of inorganic nitrate on BP in older adults. Methods: Eligible studies were searched in Cochrane Library, PubMed, Scopus, Web of Science, and Embase. Randomized controlled trials which evaluated the effect of inorganic nitrate consumption on BP in older adults were recruited. The random-effect model was used to calculate the pooled effect sizes. Results: 22 studies were included in this meta-analysis. Overall, inorganic nitrate consumption significantly reduced systolic blood pressure (SBP) by -3.90 mmHg (95% confidence interval: -5.23 to -2.57; P < 0.001) and diastolic blood pressure (DBP) by -2.62 mmHg (95% confidence interval: -3.86 to -1.37; P < 0.005) comparing with the control group. Subgroup analysis showed that the BP was significantly reduced when participants' age>65, BMI>30, or baseline BP in prehypertension stage. And both SBP and DBP decreased significantly after acute nitrate supplementation of a single dose (<1 day) or more than 1-week. However, participants with hypertension at baseline were not associated with significant changes in both SBP and DBP. Subgroup analysis of measurement methods showed that only the resting BP group showed a significant reduction in SBP and DBP, compared with the 24-h ambulatory BP monitoring (ABPM) group and daily home BP measurement group. Conclusion: These results demonstrate that consuming inorganic nitrate can significantly reduce SBP and DBP in older adults, especially in whose age > 65, BMI>30, or baseline BP in prehypertension stage.