Pharmacokinetics of nitrate and nitrite following beetroot juice consumption : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nutrition and Dietetics at Massey University, Albany, New Zealand

Abstract

Background: Nitrate (NO₃⁻) rich beetroot juice (BR) supplementation has been shown to improve cardiovascular function via reduction to nitrite (NO₂⁻) and thus the signalling molecule nitric oxide (NO). However, limited research exists for the role of inorganic NO₂⁻ contained within BR. Objective: To evaluate the individual effects of NO₃⁻ and NO₂⁻ consumed from BR on plasma [NO₃⁻]/[NO₂⁻] and various cardiovascular measures. Design: Eleven adults completed four trials; whereby they consumed 250 mL of BR containing one of the following; i) High-NO₃⁻ (572 mg NO₃⁻, 32 mg NO₂⁻); ii) Med-NO₃⁻/NO₂⁻ (280 mg NO₃⁻, 237 mg NO₂⁻); iii) Med-NO₂⁻ (43 mg NO₃⁻, 262 mg NO₂⁻); iv) Placebo (PL; 8 mg NO₃⁻, 5.8 mg NO₂⁻). Plasma [NO₃⁻]/[NO₂⁻], blood pressure (BP), heart rate (HR), mean arterial pressure (MAP), cardiac output (CO) and stroke volume (SV) were measured at baseline and every hour or second hour for 6 h post BR consumption. Outcomes: Ingestion of the high-NO₃⁻ and med-NO₃⁻/NO₂⁻ BR increased plasma [NO₂⁻] and [NO₃⁻] from 2 h, with both remaining elevated after 6h (p<0.05). Med-NO₂⁻ 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 high-NO₃⁻ at 4 h and med-NO₂⁻ at 6 h (p<0.05). However, there were no differences in SBP, DBP, HR, CO and SV between trials. Conclusion: Inorganic NO₃⁻ consumption is the critical factor in elevating plasma [NO₃⁻] or [NO₂⁻], however, both NO₂⁻ and NO₃⁻ show potential to reduce MAP. The known reduction of SBP/DBP following NO₃⁻ supplementation was not observed, making it unclear if NO₂⁻ contributes to a reduction in SBP/DBP alongside NO₃⁻.