The Connection Between Your Mouth and Your Workout

Before your next run, consider what's happening on your tongue. A specific community of bacteria living there may be doing more for your cardiovascular performance than your warm-up routine. A 2025 study found that oral nitrate-reducing capacity correlated with oxygen consumption at the ventilatory threshold at rho=0.81, p<0.001. That's a stronger correlation than most single biomarkers achieve with fitness outcomes. And most athletes have never heard of it.

The pathway that connects your saliva to your muscles

Dietary nitrate — found in high concentrations in leafy greens, beetroot, arugula, and spinach — gets absorbed in your small intestine and then concentrated in your saliva. The bacteria on your tongue reduce nitrate to nitrite. You swallow the nitrite-rich saliva, it enters the circulation, and in the low-oxygen environment of working muscle, it gets converted to nitric oxide. Nitric oxide dilates blood vessels, reduces the oxygen cost of mitochondrial ATP production, and improves the efficiency of muscle contraction. The net result is a lower oxygen demand per unit of power output — which shows up as a higher VO2 max, a higher lactate threshold power, and better endurance at high intensities.

The Stahl 2025 finding

Stahl et al. set out to understand why patients with heart failure often show blunted responses to oral nitrate supplementation. The answer turned out to be in their mouths. Oral nitrate-reducing capacity was significantly lower in the heart failure group compared to healthy age-matched controls. And across all participants, oral nitrate-reducing capacity correlated with VO2 peak at rho=0.68 and with VO2 at ventilatory threshold at rho=0.81. Your oral bacteria's nitrate-processing capacity tracks with your aerobic fitness.

Beetroot juice works — but only if your oral bacteria cooperate

The exercise science literature on dietary nitrate and performance is now substantial. Beetroot juice supplementation extended time to exhaustion by approximately 16 percent in one controlled cycling study. A 2022 meta-analysis of 1,705 participants across multiple trials found something important: practices that disrupt the oral microbiota — primarily antiseptic mouthwash — consistently reduced or eliminated the ergogenic effect of dietary nitrate. If the bacteria aren't there to convert the nitrate to nitrite, the beetroot juice does nothing for your blood pressure or your performance.

The mouthwash problem for athletes

Chlorhexidine mouthwash used for seven days dropped salivary nitrite by roughly 90 percent, reduced plasma nitrite by 25 percent, and raised systolic blood pressure by 2.3 mmHg in a controlled experiment. For an athlete who uses antiseptic mouthwash twice daily and then eats a large serving of arugula before training, the expected performance benefit from that nitrate essentially disappears. The substrate is there; the enzyme — the bacteria — isn't.

What this means practically

Dietary nitrate intake matters, and the dose-response evidence suggests it works best consumed 150 minutes or more before exercise. The oral bacteria that process that nitrate need to be present and abundant, which means avoiding broad-spectrum antiseptic oral rinses around training. And your oral nitrate-reducing capacity may be a measurable individual variable that explains why some people respond strongly to beetroot supplementation and others barely respond at all.

The tongue biome doesn't usually make it into training plans. It probably should.

Sources

Stahl ME et al. Am J Physiol Heart Circ Physiol. 2025. DOI: 10.1152/ajpheart.00567.2025. Vanhatalo A et al. Free Radic Biol Med. 2018. PMC6191927. Gomes A et al. Adv Nutr. 2022. DOI: 10.1093/advances/nmac054. Kapil V et al. Free Radic Biol Med. 2013. PMID: 23201780.