The beetroot juice story is well known: nitrates raise the availability of nitric oxide, nitric oxide lowers the oxygen cost of work, economy improves. Far less well known is who exactly carries out the first step of that chain.

Not you. Humans have no enzyme that reduces nitrate to nitrite. That work is done by bacteria living on the back of the tongue. Kill them and the chain breaks at its very first link.

What the experiments showed

Govoni et al., Nitric Oxide, 2008. Seven healthy volunteers, crossover design. Each was given sodium nitrate at 10 mg/kg, dissolved in water. In the control condition, nitrate and nitrite levels in saliva and plasma rose as expected after the load.

Then the same people rinsed their mouth with a chlorhexidine mouthwash before taking the nitrate. The result: the accumulation of nitrate itself was unaffected, but its conversion into nitrite in saliva was abolished completely, and the rise of nitrite in plasma was sharply blunted.

This is a clean mechanistic experiment: the substance was swallowed but not activated.

Woessner et al., Nitric Oxide, 2016. Twelve normotensive men (36 ± 11 years), four visits in random order a week apart. The nitrate load was 8.4 mmol in the form of beetroot juice, that is, in exactly the form athletes drink it. Water, Listerine, Cepacol and chlorhexidine were compared.

They found a stepwise reduction in nitrite in saliva and plasma as the “strength” of the mouthwash increased. So this is not a binary story of “chlorhexidine is bad, everything else is fine”: the stronger the antibacterial action, the more of the effect is cut away.

Where the evidence ends

Here it is worth being honest, because the topic is easy to overinflate.

There are essentially no direct studies of “mouthwash → running economy → performance”. What is proven is that the biochemical link — the rise of nitrite in plasma — collapses. That this link is what carries the beetroot effect through to performance has been shown in other research. The chain is completed by mechanism, not measured end to end in a single experiment.

The samples are tiny: seven and twelve people, and in Woessner's study men only.

With health rather than performance, it turned out to be more complicated. The hypothesis that mouthwashes raise blood pressure through a nitric oxide deficit has been tested systematically. Toonen et al., International Journal of Dental Hygiene, 2026: out of a hundred papers found, five met the selection criteria. In two of them systolic and diastolic pressure rose significantly after chlorhexidine, but the meta-analysis showed no significant difference (systolic: mean difference 1.56 mmHg, p = 0.17).

The correct conclusion from this is: the mechanism is real and reproducible, the clinical effect on blood pressure is not proven. For an athlete the first part matters more, because what interests them is not resting blood pressure but plasma nitrite before the start.

What to do in practice

Do not rinse your mouth with an antiseptic during a beetroot loading window. The standard scheme is juice 2–3 hours before the start, or a course over 3–6 days. Chlorhexidine in that window writes off the investment.
Remember the less obvious sources of chlorhexidine: antiseptic throat sprays and lozenges, gels after dental procedures, post-operative rinses. Same bacteria.
Ordinary brushing with toothpaste is not a problem. This is specifically about antibacterial rinses, not about hygiene as such.
If beetroot “does not work for you”, check your mouthwash. Individual response to nitrates really does vary a lot, but before blaming genetics it is worth ruling out the banal cause. The same applies to athletes who use mouthwash daily.
Do not confuse this with carbohydrate or menthol mouth rinsing. Those work through receptors in the mouth and have nothing to do with the nitrate pathway.
Do not run experiments with dropping chlorhexidine your dentist prescribed. If it was prescribed for a reason, the sensible move is to shift the beetroot loading, not the treatment.

Key points

Nitrate is reduced to nitrite by bacteria on the back of the tongue — humans have no enzyme of their own for this reaction.
Govoni, 2008 (n = 7): a chlorhexidine mouthwash completely abolished the conversion of nitrate to nitrite in saliva and sharply blunted the rise of nitrite in plasma.
Woessner, 2016 (n = 12, beetroot juice load of 8.4 mmol): the reduction in nitrite is stepwise — the stronger the antibacterial action, the greater the loss.
There are almost no direct studies of “mouthwash → running economy”; the chain is completed by mechanism.
A 2026 meta-analysis (5 studies) did not confirm a significant effect of chlorhexidine on blood pressure.
Practical conclusion: antiseptic rinses and beetroot loading should not fall into the same time window.

Sources: Govoni M. et al. «The increase in plasma nitrite after a dietary nitrate load is markedly attenuated by an antibacterial mouthwash», Nitric Oxide, 2008. https://doi.org/10.1016/j.niox.2008.08.003 · Woessner M. et al. «A stepwise reduction in plasma and salivary nitrite with increasing strengths of mouthwash following a dietary nitrate load», Nitric Oxide, 2016. https://doi.org/10.1016/j.niox.2016.01.002 · Toonen E. et al. «The Effect of Chlorhexidine Mouthwash on Blood Pressure: A Systematic Review and Meta-Analysis», International Journal of Dental Hygiene, 2026. https://doi.org/10.1111/idh.70035