A randomized clinical trial of the effects of leafy green vegetables and inorganic nitrate on blood pressure

Background: A diet rich in fruits and vegetables is associated with lowering of blood pressure (BP), but the nutrient(s) responsible for these effects remain unclear. Research suggests that inorganic nitrate present in leafy green vegetables is converted into NO in vivo to improve cardiovascular function. Objective: In this study, we evaluated the effect of leafy green vegetables on BP in subjects with elevated BP, with the aim of elucidating if any such effect is related to their high nitrate content. Design: We enrolled 243 subjects, 50-70 y old, with a clinic systolic BP (SBP) of 130-159 mm Hg. After a 2-wk run-in period on a nitrate-restricted diet the subjects were randomly assigned to receive 1 of the following 3 interventions daily for 5 wk: low-nitrate vegetables + placebo pills, low-nitrate vegetables + nitrate pills (300 mg nitrate), or leafy green vegetables containing 300 mg nitrate + placebo pills. The primary end point measure was the difference in change in 24 h ambulatory SBP between the groups. Results: A total of 231 subjects (95%) completed the study. The insignificant change in ambulatory SBP (mean +/- standard deviation) was -0.6 +/- 6.2 mm Hg in the placebo group, -1.2 +/- 6.8 mm Hg in the potassium nitrate group, and -0.5 +/- 6.6 mm Hg in the leafy green vegetable group. There was no significant difference in change between the 3 groups. Conclusions: A 5-wk dietary supplementation with leafy green vegetables or pills containing the same amount of inorganic nitrate does not decrease ambulatory SBP in subjects with elevated BP.