Background: Nitrate (NO3−)-rich beetroot (BR) juice supplementation has been shown to improve cardiovascular function via reduction to nitrite (NO2−) and then to the bioactive molecule nitric oxide (NO). However, limited research exists for the role of inorganic NO2− that is contained naturally within BR. Objective: As BR juice can naturally contain both NO3− and NO2− the objective of this study was to evaluate the individual effects of NO3− and NO2− consumed from BR on plasma [NO3−]/[NO2−] and their subsequent effects on various cardiovascular measures. Design: In four separate treatments, 11 healthy adults consumed 250 mL of BR containing one of the following: (i) high NO3−, low NO2− (HL; 572 mg NO3−, 32 mg NO2−); (ii) medium NO3−, medium NO2− (MM; 280 mg NO3−, 237 mg NO2−); (iii) low NO3−, medium NO2− (LM; 43 mg NO3−, 262 mg NO2−); (iv) placebo (PL; low NO3−, low NO2−: 8 mg NO3−, 5.8 mg NO2−). Plasma [NO3−]/[NO2−], blood pressure, heart rate, mean arterial pressure (MAP), cardiac output and stroke volume were measured at baseline and every hour or second hour for 6 h post-BR consumption. Outcomes: Ingestion of the HL and MM BR increased plasma [NO2−] and [NO3−] after 2 h, with both remaining elevated after 6 h (p < 0.05). LM increased plasma [NO3−] (p < 0.05) but did not increase plasma [NO2−] compared to PL (p = 0.177). MAP was lower following the consumption of HL at 4 h and LM at 6 h (p < 0.05). Conclusion: Inorganic NO3− consumption is the critical factor in elevating plasma [NO3−] and [NO2−]; however, both NO2− and NO3− show potential to reduce MAP. The known reduction of systolic blood pressure (SBP)/diastolic blood pressure (DBP) following NO3− supplementation was not observed, making it unclear if NO2− contributes to a reduction in SBP/DBP alongside NO3−.
Role of nitrate and nitrite for production and consumption of nitric oxide during denitrification in soil