Another study looking at beetroot juice (1) has been published in the American Journal of Applied Physiology.
6 Days of 500 ml/ day of beetroot juice increased time to exhaustion during severe-intensity running by 15% in study subjects.
The results are attributed to the high nitrate levels in beetroot juice, which act on reducing the oxygen cost of running.
Blood pressure was also reduced: Systolic BP decreased from 129 to 124 mmHg after the 6 days of beetroot juice.
A different study published in Medicine and Science In Sports and Exercise (2) looked at the effect of 500 ml of beetroot juice consumed 2.5 hours before cycling time trials.
I was more interested in this study because it tested beetroot juice in a more real world competitive challenge. When an earlier study (2009 (3)) came out suggesting increased anaerobic performance from 1 week of beetroot juice consumption I of course couldn't wait to try it.
Once I trained my pallet to like the taste it was pretty good.. a little tart at first. A friend of mine who tried it said they thought it tasted great right away. My results? I couldn't tell. Nothing showed up in my training measurements, but I didn't do lab testing, or controlled time trials. I keep meticulous records of my lactate, heart rate, and power output though, and over the 4 or 5 times I tried a one week trial of 500 ml/ day of pure beetroot juice no notable increase in performance occurred beyond what I usually see. Subjectively I can say that I could not detect any extra feeling of short term power endurance.
The cycling time trial performance study (2) showed a 2.8 to 2.7% increase in performance for 4 and 16.2 km time trials, pretty big change for doing nothing other than drinking 500 ml of beetroot juice 2.5 hours prior to competition. This study did not do the longer one week of daily beetroot juice consumption trial like the other two studies I cite here so who knows, maybe there would have been a larger increase in performance with the one week trial.
(1) Dietary nitrate supplementation reduces the O2 cost of walking and running: a placebo-controlled study
(2)Acute Dietary Nitrate Supplementation Improves Cyc... [Med Sci Sports Exerc. 2011] - PubMed result
(3) Dietary nitrate supplementation reduces the O2 cos... [J Appl Physiol. 2009] - PubMed result