Nitrate supplementation has become increasingly popular in recent years among athletes and fitness enthusiasts alike. Its popularity is not without merit as previous research (using beetroot) has shown that athletes can benefit from a reduction in the oxygen cost of submaximal exercise; thereby increasing overall endurance and tolerance to high-intensity work. A new study published in the March 2015 issue of the Federation of American Societies for Experimental Biology journal helps shed new light on how some nitrate supplements may work, and why they potentially increase performance. The team found that they essentially decrease the viscosity of circulating blood, aiding in blood flow, while simultaneously ensuring tissue oxygen requirements are not compromised. "Our research sheds new light on how oxygen delivery to bodily tissues is controlled to support mammalian life, and what role the kidneys and the liver play in achieving this," said Andrew Murray, Ph.D., a researcher from the Department of Physiology, Development and Neuroscience at the University of Cambridge, United Kingdom.
The researchers examined the effects of nitrate supplementation on circulating hemoglobin concentrations (oxygen-transporting component in blood) in four groups of rats, which were housed in either normoxic or hypoxic (low oxygen) conditions. The rats were either given sodium nitrate or sodium chloride as a control. Hypoxia is known to elevate hemoglobin levels as a defense response to transport the low available oxygen more effectively, but a moderate dose of sodium nitrate suppressed this effect (denoting improved oxygen availability/efficiency). Interestingly, the sodium nitrate also lowered hemoglobin levels among the rats in the normoxic group. However, at higher doses, hemoglobin levels began to rise again within all of the groups.
The researchers found that the suppression of hemoglobin (with moderate nitrate dosage) was due to enhanced liver oxygenation and a consequent suppression in the hormone erythropoietin (EPO). EPO functions to control red blood cell production and has been the focus during blood doping practices that attempt to stimulate its activity. When the hemoglobin levels began to rise with higher nitrate dosage, this was because the kidneys ended up becoming relatively hypoxic and acted to reverse the effect produced by the liver. Evidently, there is a saturation point where some organs cannot keep up with the new endurance potential and act to protect essential tissues - so moderate doses appear optimal. "This doesn't mean that taking a nitrate supplement will transform you into the next Marshawn Lynch," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. "What it does mean, however, is that we're beginning to understand the science behind why some people feel they turn into the Seahawk's 'Beast Mode' when taking these supplements."