The Effects of Dietary Nitrate (Beetroot Juice) Supplementation on Exercise Performance: A Review

Abstract

Nitric oxide (NO) is a potent vasodilator that increases blood flow and induces various intracellular actions such as increased mitochondrial and contractile efficiency. NO bioavailability may be increased by direct consumption of dietary nitrate and its sequential reduction to nitrite, a regulator of NO-induced hypoxic signaling. Dietary nitrate consumption reduces blood pressure, protects from ischemia-reperfusion injury, and improves endothelial dysfunction. Recently, the popularity of dietary nitrate as an ergogenic aid has been increased dramatically. Most exercise studies have administered dietary nitrate in the form of beetroot juice containing 5-8 mmol of nitrate and a few studies have used sodium and potassium nitrate (8-10 mg/kg). The most prominent and consistent effects of dietary nitrate supplementation is a reduction in the oxygen cost of exercise and an increase in exhaustion time at submaximal workloads. This effect was observed after either a single bolus (2-3 h prior to exercise) or a long-term (2-15 days) supplementation. The ergogenic effects of beetroot supplementation appear to be dose-dependent and are most often observed after long-term ingestion (approximately 6 days), at high exercise intensities and in less fit individuals. The ergogenic value of beetroot supplementation in endurance athletes is not clear; many studies have documented no improvements and a few studies an enhanced performance (0.4% to 3%) in time- and distance-trials. Clearly, more research is needed to document (i) the optimal dosage of beetroot ingestion for enhancing exercise performance in athletes, (ii) the effects of dietary nitrate consumption on training adaptations, (iii) the efficacy of beetroot supplementation in increasing exercise tolerance in individuals with chronic disease, and (iv) the safety of long-term beetroot consumption.