Pharmacokinetics of Nitrate and Nitrite Following Beetroot Juice Drink Consumption

Abstract

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 -.