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INTRODUCTION Available evidence indicates that ketone bodies may improve sleep quality. Therefore, we determined whether ketone ester (KE) intake could counteract sleep disruptions induced by strenuous exercise. METHODS Ten well-trained cyclists with good sleep quality participated in a randomised crossover design consisting of two experimental sessions each involving a morning endurance training and an evening high-intensity interval training ending one hour before sleep, after which polysomnography was performed overnight. Post-exercise and 30 min before sleeping time, subjects received either 25 g KE (EXKE) or a placebo drink (EXCON). A third session without exercise, but with placebo supplements (RCON) was added to evaluate the effect of exercise per se on sleep. RESULTS Blood D-β-hydroxybutyrate concentrations transiently increased to ~3 mM post-exercise and during the first part of the night in EXKE but not in EXCON or RCON. Exercise significantly reduced REM sleep by 26% (p = 0.001 vs. RCON) and increased wakefulness after sleep onset (WASO) by 95% (p = 0.004 vs. RCON). Interestingly, KE improved sleep efficiency by 3% (p = 0.040 vs. EXCON) and counteracted the exercise-induced decrease in REM sleep (p = 0.011 vs. EXCON) and the increase in WASO (p = 0.009 vs. EXCON). This was accompanied by a KE-induced increase in dopamine excretion (p = 0.033 vs. EXCON), which plays a pivotal role in sleep regulation. In addition, exercise increased sleep spindle density by 36% (p = 0.005 vs. RCON) suggesting an effect on neural plasticity processes during sleep. CONCLUSIONS These data indicate that KE ingestion improves sleep efficiency and quality following high-intensity exercise. We provide preliminary evidence that this might result from KE-induced increases in dopamine signalling.