Pharmacokinetics of Nitrate and Nitrite Following Beetroot Juice Drink Consumption

Background: Nitrate (NO(3)(−))-rich beetroot (BR) juice supplementation has been shown to improve cardiovascular function via reduction to nitrite (NO(2)(−)) and then to the bioactive molecule nitric oxide (NO). However, limited research exists for the role of inorganic NO(2)(−) that is contained naturally within BR. Objective: As BR juice can naturally contain both NO(3)(−) and NO(2)(−) the objective of this study was to evaluate the individual effects of NO(3)(−) and NO(2)(−) consumed from BR on plasma [NO(3)(−)]/[NO(2)(−)] 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 NO(3)(−), low NO(2)(−) (HL; 572 mg NO(3)(−), 32 mg NO(2)(−)); (ii) medium NO(3)(−), medium NO(2)(−) (MM; 280 mg NO(3)(−), 237 mg NO(2)(−)); (iii) low NO(3)(−), medium NO(2)(−) (LM; 43 mg NO(3)(−), 262 mg NO(2)(−)); (iv) placebo (PL; low NO(3)(−), low NO(2)(−): 8 mg NO(3)(−), 5.8 mg NO(2)(−)). Plasma [NO(3)(−)]/[NO(2)(−)], 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 [NO(2)(−)] and [NO(3)(−)] after 2 h, with both remaining elevated after 6 h (p < 0.05). LM increased plasma [NO(3)(−)] (p < 0.05) but did not increase plasma [NO(2)(−)] 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 NO(3)(−) consumption is the critical factor in elevating plasma [NO(3)(−)] and [NO(2)(−)]; however, both NO(2)(−) and NO(3)(−) show potential to reduce MAP. The known reduction of systolic blood pressure (SBP)/diastolic blood pressure (DBP) following NO(3)(−) supplementation was not observed, making it unclear if NO(2)(−) contributes to a reduction in SBP/DBP alongside NO(3)(−).