Beetroot juice versus chard gel: A pharmacokinetic and pharmacodynamic comparison of nitrate bioavailability

Dietary supplementation with inorganic nitrate (NO₃^-) has been shown to induce a multitude of advantageous cardiovascular and metabolic responses during rest and exercise. While there is some suggestion that pharmacokinetics may differ depending on the NO₃^- source ingested, to the best of our knowledge this has yet to be determined experimentally. Here, we compare the plasma pharmacokinetics of NO₃^-, nitrite (NO₂^-), and total nitroso species (RXNO) following oral ingestion of either NO₃^- rich beetroot juice (BR) or chard gels (GEL) with the associated changes in blood pressure (BP). Repeated samples of venous blood and measurements of BP were collected from nine healthy human volunteers before and after ingestion of the supplements using a cross-over design. Plasma concentrations of RXNO and NO₂^- were quantified using reductive gas-phase chemiluminescence and NO₃^- using high pressure liquid ion chromatography. We report that, [NO₃^-] and [NO₂^-] were increased and systolic BP reduced to a similar extent in each experimental arm, with considerable inter-individual variation. Intriguingly, there was a greater increase in [RXNO] following ingestion of BR in comparison to GEL, which may be a consequence of its higher polyphenol content. In conclusion, our data suggests that while differences in circulating NO₂^- and NO₃^- concentrations after oral administration of distinct NO₃^--rich supplementation sources are moderate, concentrations of metabolic by-products may show greater-than-expected variability; the significance of the latter observation for the biological effects under study remains to be investigated.