A Single Night in Hypoxia Either with or without Ketone Ester Ingestion Reduces Sleep Quality without Impacting Next-Day Exercise Performance.

Background: Sleeping at altitude is highly common in athletes as an integral part of altitude training camps or sport competitions. However, concerns have been raised because of expected 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 after 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 3000 m while receiving either KE or placebo postexercise and presleep. Sleep was evaluated using polysomnography, whereas next-day exercise performance was assessed through a 30-min all-out time trial (TT 30' ). 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 SpO 2 throughout the first part of the night, but did not alter hypoxia-induced sleep dysregulations. Neither KE nor nocturnal hypoxia affected TT 30' performance, but nocturnal hypoxia hampered heart rate recovery after TT 30' .

Conclusions: We observed that sleeping at a 3000 m altitude 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 might impair next-day exercise recovery. KE alleviated nocturnal hypoxemia only when SpO 2 values dropped below ~85%, but this did not translate into improved sleep or next-day exercise performance.