Benefits
Blood pressure reduction
In a 2013 review pooling 16 trials and 254 people, nitrate from beetroot lowered the top (systolic) number by about 4.4 mmHg (95% CI -5.9 to -2.8, P<0.001). The bottom (diastolic) number fell only about 1.1 mmHg, and that change was not statistically significant (P=0.06). Most of those trials lasted from a couple of hours to 15 days. The longest and best controlled study gave 250 mL of beetroot juice a day for 4 weeks to 68 people with diagnosed high blood pressure and lowered 24-hour blood pressure by about 7.7/5.2 mmHg. That is research in patients, not a promise about what beetroot does for someone whose blood pressure is already normal.
Athletic endurance
Two small placebo-controlled crossover studies support this. In 9 healthy active men drinking about 0.5 L of juice a day for 6 days, the oxygen cost of walking fell from 0.87 to 0.70 L/min and time to exhaustion rose about 15%, from 7.6 to 8.7 minutes. In 8 men aged 19 to 38 taking 500 mL a day for 6 days, the oxygen uptake gain during moderate exercise fell about 19% and time to exhaustion rose from 583 to 675 seconds. The findings replicate each other, but both groups were tiny, all male, and tested over only 6 days.
Muscle efficiency
What was actually measured in people is simpler: muscles used less oxygen for the same amount of work. Improved mitochondrial efficiency, and a larger effect in fast-twitch fibres, are proposed explanations for that observation, not findings from the human studies cited on this page.
Brain blood flow: not tested in the cited studies
None of the studies cited on this page measured blood flow to the brain, reaction time or thinking skills. Widening blood vessels could in theory affect brain blood flow, but that idea has not been tested by the research listed here, so treat it as unproven rather than as a benefit of taking beetroot.
Mechanism of action
Nitrate-nitrite-nitric oxide pathway
Dietary nitrate is reduced to nitrite by bacteria living in the mouth, then converted to nitric oxide (NO) by tissue enzymes under low-oxygen conditions. Because that first step depends on mouth bacteria, antibacterial mouthwash can wipe out the effect. NO activates soluble guanylate cyclase, increasing cGMP and causing smooth muscle relaxation and vasodilation.
Mitochondrial efficiency improvement
One proposed explanation is that small amounts of nitric oxide interact with cytochrome c oxidase (Complex IV) and shift how mitochondria use oxygen, lowering the oxygen cost of producing energy. This is a working theory for the drop in oxygen use seen during exercise, not something the human studies cited here measured directly.
EPO-independent oxygen delivery
Wider blood vessels may send more blood to working muscles, improving oxygen delivery without any change in red blood cell mass. Beetroot is a food, not a banned substance, but the studies cited here measured oxygen cost and time to exhaustion in a handful of men in a lab, not competitive results.
Clinical trials
Two randomised crossover trials in which participants drank about 500 mL of beetroot juice a day for 6 days. The walking and running trial used nitrate-depleted beetroot juice as the placebo, so the only difference between the drinks was the nitrate. (Lansley et al. 2011 and Bailey et al. 2009, J Appl Physiol)
9 healthy active men in one trial and 8 men aged 19 to 38 in the other. No women were studied.
In the 9-man trial the oxygen cost of walking fell from 0.87 to 0.70 L/min and time to exhaustion rose about 15%, from 7.6 to 8.7 minutes. In the 8-man trial the oxygen uptake gain during moderate exercise fell about 19% and time to exhaustion rose from 583 to 675 seconds. The 9-man trial used nitrate-free beetroot juice as the placebo, which makes it clear the nitrate itself is responsible. Limitations: both samples were very small, all male, and tested over just 6 days, so how much this matters outside the lab is still unknown.
Pooled analysis of 16 clinical trials examining inorganic nitrate or beetroot juice on blood pressure in adults with normal or elevated BP. (Siervo, Lara, Ogbonmwan, J Nutr)
254 adults in total across 16 trials, with normal or raised blood pressure.
Systolic (top number) blood pressure fell by 4.4 mmHg (95% CI -5.9 to -2.8, P<0.001), with a dose-response pattern: more nitrate, bigger drop. Diastolic (bottom number) blood pressure fell only 1.1 mmHg (95% CI -2.2 to 0.1) and that result was not statistically significant (P=0.06). The pooled trials ran from 2 hours to 15 days, so this is short-term evidence and does not show that the effect keeps up over months.