Influence of acute dietary nitrate supplementation timing on nitrate metabolism, central and peripheral blood pressure and exercise tolerance in young men.

Purpose: Dietary nitrate (NO ₃ ^- ) supplementation can lower systolic blood pressure (SBP) and improve exercise performance. Salivary flow rate (SFR) and pH are key determinants of oral NO ₃ ^- reduction and purported to peak in the afternoon. We tested the hypotheses that NO ₃ ^- -rich beetroot juice (BR) would increase plasma [nitrite] ([NO ₂ ^- ]), lower SBP and improve exercise performance to a greater extent in the afternoon (AFT) compared to the morning (MORN) and evening (EVE).
Method: Twelve males completed six experimental visits in a repeated-measures, crossover design. NO ₃ ^- -depleted beetroot juice (PL) or BR (~ 13 mmol NO ₃ ^- ) were ingested in the MORN, AFT and EVE. SFR and pH, salivary and plasma [NO ₃ ^- ] and [NO ₂ ^- ], brachial SBP and central SBP were measured pre and post supplementation. A severe-intensity exercise tolerance test was completed to determine cycling time to exhaustion (TTE).
Results: There were no between-condition differences in mean SFR or salivary pH. The elevation in plasma [NO ₂ ^- ] after BR ingestion was not different between BR-MORN, BR-AFT and BR-EVE. Brachial SBP was unchanged following BR supplementation in all conditions. Central SBP was reduced in BR-MORN (- 3 ± 4 mmHg), BR-AFT (- 4 ± 3 mmHg), and BR-EVE (- 2 ± 3 mmHg), with no differences between timepoints. TTE was not different between BR and PL at any timepoint.
Conclusion: Acute BR supplementation was ineffective at improving TTE and brachial SBP and similarly effective at increasing plasma [NO ₂ ^- ] and lowering central SBP across the day, which may have implications for informing NO ₃ ^- supplementation strategies.
(© 2023. The Author(s).)