Kaempferol and Exercise Economy: A Promising First Trial

Kaempferol may have reduced the oxygen cost of exercise in trained cyclists after a single 10 mg dose. That is an unusually interesting result in sports nutrition: trained athletes rarely gain much from supplements that promise to make exercise feel metabolically cheaper. But the finding comes from one small, industry-linked trial in 16 men. It deserves attention, not a spot in every race-day pill organizer.

Exercise economy describes how much oxygen an athlete needs to produce a given amount of work. If two cyclists hold the same power but one uses less oxygen, that rider has more physiological room before reaching a limit. Improving that ratio can matter in endurance events, especially for athletes whose training has already pushed their VO₂max near its practical ceiling.

A flavonoid found through a targeted screen

The route to this trial was more disciplined than the usual supplement story. Researchers screened 65 phytochemicals from extracts of 314 highland crop species in low-oxygen cell models, looking for compounds that increased intracellular ATP production. Kaempferol emerged as the compound that activated mitochondrial metabolism in that screen. The researchers then moved to human testing rather than treating a cell result as proof of athletic benefit.

Kaempferol occurs in foods including kale and onions, often as glycosides rather than as free kaempferol, or aglycone. Highland-grown cabbage reportedly contains more of it than lower-altitude equivalents. That makes for a plausible biological origin story, but eating cabbage and swallowing a prepared research formulation are not interchangeable exposures.

What the cyclist trial found

In Okita et al. (2025), 16 well-trained male cyclists completed a randomized, double-blind, placebo-controlled crossover trial. Each participant took either 10 mg of kaempferol aglycone or placebo while fasted, three hours before exercise testing. The dose came from a quinoa-derived glycoside processed enzymatically into an aglycone, and the three-hour timing matched the reported plasma peak. Trial periods were separated by at least three days; plasma testing found little residual compound at 24 hours.

The cyclists exercised at five constant workloads spanning 25% to 125% of VO₂max. The investigators measured pulmonary gas exchange with Douglas bags and mass spectrometry, a rigorous method for measuring oxygen uptake. Compared with placebo, kaempferol significantly lowered oxygen uptake at submaximal intensities and improved time to exhaustion at supramaximal workloads.

The result is internally coherent: less oxygen use at easier workloads appeared alongside longer tolerance of very hard work. It is still one acute trial in 16 people.

The published evidence available here does not provide the actual VO₂ reduction in mL/kg/min, the time-to-exhaustion difference in seconds, confidence intervals, or p-values. That omission matters. Without those numbers, athletes cannot judge whether the effect was a tiny laboratory shift or large enough to compete with established ergogenic strategies. They also cannot directly compare it with the roughly 2% to 3% submaximal VO₂ reductions often reported for dietary nitrate.

A plausible mechanism, still unproven in humans

The cell screen points toward mitochondrial ATP production under low-oxygen conditions. In theory, more ATP produced per unit of oxygen could reduce whole-body oxygen consumption during steady exercise. The human trial's oxygen-uptake result fits that theory, but it does not prove it.

The cyclists did not undergo muscle biopsies or measurements of mitochondrial coupling, ATP-to-ADP ratios, or lactate kinetics. The study therefore cannot show whether kaempferol changed electron-transport efficiency, mitochondrial membrane stability, AMPK signaling, or something else. Pulmonary VO₂ is an important physiological outcome; it is not a direct readout of a specific cellular mechanism.

The 10 mg dose was selected after preliminary human work suggested performance reached a plateau somewhere between 10 and 50 mg. That does not establish an optimal dose for athletes, nor does it tell us what happens with daily use. Every human kaempferol study in this research program used acute dosing. Repeated dosing could preserve the effect, blunt it, or produce a different response altogether.

The flavonoid track record calls for restraint

Kaempferol is not arriving in a class with a clean record. A 2022 systematic review and meta-analysis by d'Unienville et al. found that dietary nitrate consistently reduced submaximal VO₂ and improved endurance performance across randomized trials, while polyphenols produced inconsistent results. Nitrate has a well-supported nitric-oxide pathway and a larger body of performance research. Kaempferol has one positive crossover trial.

Related flavonoid studies also point to compound-specific effects rather than a general "flavonoids improve endurance" rule. In a double-blind crossover trial of high-level male basketball players, Bourdas et al. (2024) tested an acute mangiferin-quercetin combination and reported mixed performance results, with some evidence of benefit on basketball-relevant tests. The study supports the possibility that an acute flavonoid intervention can affect performance, but its population, combination product, and endpoints differ from the cyclist study.

In trained cyclists, Kurtz et al. (2025) found that quercetin plus citrulline changed nitric-oxide metabolites and antioxidant biomarkers without establishing clear VO₂-economy benefits. Those biomarkers show that the intervention affected biology; they do not establish improved performance. The contrast with kaempferol may reflect different compounds, a combination intervention rather than kaempferol alone, and different endpoints. It still weakens any claim that flavonoids reliably reduce oxygen cost in trained cyclists.

Quercetin has also shown biological effects outside acute endurance economy. In a placebo-controlled study of exercise-induced muscle damage, Sgrò et al. (2022) reported changes in IGF-I and IGF-II after eccentric exercise. Recovery-related growth-factor changes are not evidence that quercetin or kaempferol improves aerobic performance. They illustrate why the flavonoid category is too broad to treat as one intervention.

Why the result may not translate to competition

Constant-load cycling to voluntary exhaustion helps researchers detect physiological changes, but it does not reproduce a self-paced race. Time trials better reflect competition because athletes continuously adjust power in response to fatigue, discomfort, tactics, and pacing. A lower VO₂ at a fixed workload could help a time trial, but the kaempferol study did not test that question.

Its participants were well-trained male cyclists with VO₂max values around 58 mL/kg/min. We do not know whether women, recreational athletes, runners, team-sport players, or older competitors respond similarly. The study also had no independent replication, no reported power calculation in the available publication details, and no chronic dosing arm.

Conflict of interest deserves a plain reading. Otsuka Pharmaceutical supplied the capsules and hosted the ethics approval, and the related kaempferol work comes from the same closely affiliated research group and industry partner. That arrangement does not make the data false. It does mean an independent, adequately powered replication should carry more weight than further work from the same network.

Should athletes try it?

Kaempferol is worth watching, not relying on. The tested intervention was 10 mg of a specially prepared quinoa-derived aglycone, taken fasted three hours before exercise. Commercial products vary by plant source and by whether they contain aglycone or glycoside forms. Current evidence does not establish that a label reading "10 mg kaempferol" produces the same blood exposure as the research product.

Food sources remain sensible foods, but no trial shows that dietary kaempferol from kale, onions, or similar foods reproduces the trial result. Athletes seeking a better-established oxygen-economy intervention have stronger evidence for dietary nitrate than for polyphenols as a class. Kaempferol's first human signal is unusually coherent and methodologically serious. It becomes practical evidence only if independent trials confirm it with quantified effects, self-paced performance outcomes, women and other athlete groups, and repeated dosing.