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 (View the MathML sourceO2) 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 View the MathML sourceO2 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 View the MathML sourceO2 remained reduced. Conclusion Up to ∼4 weeks supplementation with 6 but not 3 mmol NO3− can reduce submaximal exercise View the MathML sourceO2. A comparable reduction in submaximal exercise View the MathML sourceO2 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−].