Researchers from the United Kingdom tested the effects of dietary nitrite supplementation on exercise stamina and oxygen consumption. In a double-blind, randomized cross over study, active men supplemented for 6 days with either 500 mL of beetroot juice (which has a high nitrite concentration) or black current juice cordial shown to have negligible nitrite levels. They were instructed to sip the beverages throughout the day. During the last 3 days of each 6-day supplement period, they performed a series of moderate and high intensity cycling.
Beetroot juice resulted in a 96% increase in plasma levels of nitrate, and also reduced
systolic blood pressure compared to placebo. Oxygen uptake by the lungs during moderate intensity cycling was reduced by 16% in the beetroot juice trial. Most importantly, beetroot juice enabled subjects to exercise during a high intensity bout to exhaustion 16% longer (11 min 15 sec versus 5 min 43 sec for placebo).
The findings show that supplementing with beetroot juice as a rich source of dietary nitrite allows for greater amounts of exercise with less oxygen consumption. This translates into greater efficiency and allows athletes to feel less tired while exercising. Exactly how dietary nitrites achieve this effect remains unclear, but the researchers note that altering the oxygen cost of exercise is not something easily impacted, indicating this is a novel approach to improving exercise capacity.
Reference: Bailey SJ, Winyard P, Vanhatalo A, Blackwell JR, Dimenna FJ, Wilkerson DP, Tarr J, Benjamin N, Jones AM. Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans. J Appl Physiol. 2009 Oct;107(4):1144-55.