Dose-dependent effects of dietary nitrate on the oxygen cost of moderate-intensity exercise: Acute vs. chronic supplementation.

Purpose: To investigate whether chronic supplementation with a low or moderate dose of dietary nitrate (NO3(-)) reduces submaximal exercise oxygen uptake (V˙O2) and to assess whether or not this is dependent on acute NO3(-) administration prior to exercise.

Methods: Following baseline tests, 34 healthy subjects were allocated to receive 3 mmol NO3(-), 6 mmol NO3(-) or placebo. Two hours following the first ingestion, and after 7, 28 and 30 days of supplementation, subjects completed two moderate-intensity step exercise tests. On days 28 and 30, subjects in the NO3(-) groups completed the test 2 h post consumption of a NO3(-) dose (CHR + ACU) and a placebo dose (CHR).

Results: Plasma nitrite concentration ([NO2(-)]) was elevated in a dose-dependent manner at 2 h, 7 days and 28-30 days on the CHR + ACU visit. Compared to pre-treatment baseline, 6 mmol NO3(-) reduced the steady-state V˙O2 during moderate-intensity exercise by 3% at 2 h (P = 0.06), 7 days and at 28-30 days (both P < 0.05) on the CHR + ACU visit, but was unaffected by 3 mmol NO3(-) at all measurement points. On the CHR visit in the 6 mmol group, plasma [NO2(-)] had returned to pre-treatment baseline, but the steady-state V˙O2 remained reduced.

Conclusion: Up to ∼4 weeks supplementation with 6 but not 3 mmol NO3(-) can reduce submaximal exercise V˙O2. A comparable reduction in submaximal exercise V˙O2 following chronic supplementation with 6 mmol NO3(-) can be achieved both with and without the acute ingestion of NO3(-) and associated elevation of plasma [NO2(-)].