A single night in hypoxia either with or without ketone ester ingestion reduces sleep quality without impacting next day exercise performance

Background: Sleeping at (simulated) altitude is highly common in athletes as an integral part of altitude training camps or sport competitions. However, it is also often feared due to proclaimed negative effects on sleep quality, thereby potentially hampering exercise recovery and next-day exercise performance. We recently showed that ketone ester (KE) ingestion beneficially impacted sleep following strenuous, late evening exercise in normoxia, and alleviated hypoxemia. Therefore, we hypothesized that KE ingestion may be an effective strategy to attenuate hypox(em)ia-induced sleep dysregulations. Methods: Eleven healthy, male participants completed three experimental sessions including normoxic training and subsequent sleep in normoxia or at a simulated altitude of 3,000m while receiving either KE or placebo post-exercise and pre-sleep. Sleep was evaluated using polysomnography, while next-day exercise performance was assessed through a 30-min all-out time trial (TT30). Physiological measurements included oxygen status, heart rate variability, ventilatory parameters, blood acid-base balance and capillary blood gases. Results: Hypoxia caused a ~3% drop in sleep efficiency, established through a doubled wakefulness after sleep onset and a ~22% reduction in slow wave sleep. KE ingestion alleviated the gradual drop in SpO2 throughout the first part of the night, but did not alter hypoxia-induced sleep dysregulations. Neither KE, nor nocturnal hypoxia affected TT30 performance, but nocturnal hypoxia hampered heart rate recovery following TT30. Conclusion: We observed that sleeping at 3,000m altitude already impairs sleep efficiency. Although this hypoxia-induced sleep disruption was too subtle to limit exercise performance, we for the first time indicate that sleeping at altitude impairs next-day exercise recovery. KE alleviated nocturnal hypoxemia whenever SpO2 values dropped below ~85%, but this did not translate into improved sleep or next-day exercise performance.