Earlier this week we discussed the positive effects of nitric oxide on elderly muscles.
Other research suggests that nitric oxide can have more beneficial effects and not just in elderly persons.
A recent study from the University of Exeter which investigated the effects of beetroot juice on endurance supports this.
Nitric oxide can be formed by metabolic conversion from dietary nitrates. Vegetables are a rich source of these nitrates, especially beetroot juice.
Earlier studies suggested that ingestion of beetroot juice before exercise may improve performance.
However, these studies performed so called time-to-exhaustion protocols. This means that the subjects had to exercise at a set intensity until they could not maintain that intensity anymore.
However, there are no competitive sports in which the goal is to keep going at a certain speed as long as possible. Rather, the goal is to cover a certain distance as fast as possible. Therefore, time-to-exhaustion protocols are not a good measure for real performance.
Therefore, this study used a time-trial protocol. This means that the subjects had to complete a set distance in the shortest time possible. The results of such protocols translate well to actual race performance.
In addition, these earlier studies on beetroot juice compared it to a placebo supplement that did not contain beetroot juice. Therefore, those studies could not determine if it were the nitrates in the beetroot juice, or some other ingredient(s) which improved the performance.
In this study, the researchers compared nitrate rich beetroot juice to nitrate depleted beetroot juice. As the only difference between the supplements was the amount of nitrates, any effects measured could be attributed to them specifically.
The researchers instructed the subjects to ingest 0,5 L of beetroot juice 2,7 h before the time trail. This time was chosen because it takes 2,5-3,0 h before the highest value of nitric oxide in blood is reached, as it takes some time to convert the nitrates into nitric oxide.
The subjects were asked not to use any chewing gum or mouthwash. These are known to eradicate the oral bacteria that mediate the conversion of nitrates to nitric oxide.
When the subjects used the nitrate rich beetroot juice, their time on the 4 km and 16 km time trail was decreased by 2,8% and 2,7% respectively. The figure below displays the results for the 4 km trail:
The researchers concluded that the beetroot juice was effective to increase athletic performance and that this effect could indeed be contributed to the nitrates.
They mention that there is some questiosn regarding the the effects of nitrates on human health, but that it is unlikely that increased consumption of nitrate rich vegetables is harmful.