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 ^- .