Circadian disruption in astronauts: Causes, molecular mechanisms, and neurocognitive consequences

Spaceflight presents a multitude of challenges that disrupt astronauts' circadian rhythms, frequently leading to disturbed sleep and impaired cognitive functioning. This systematic review, conducted in accordance with PRISMA guidelines, synthesizes findings from 65 studies (including 47 included in the quantitative synthesis) to examine the multifactorial causes and consequences of circadian and sleep disturbances in space environments. Environmental stressors such as microgravity, radiation, confined spaces, noise, and altered light-dark cycles are critically evaluated alongside biological mechanisms including metabolic alterations, reduced melatonin secretion, and dysregulation of key circadian clock genes (PER2, BMAL1). These disruptions contribute to sleep disorders such as insomnia, sleep fragmentation, and reduced sleep efficiency. The resulting sleep deficits are shown to negatively impact cognitive domains including attention, decision-making, memory, spatial awareness, and problem-solving. This review further highlights the need for effective, evidence-based countermeasures to mitigate sleep disturbances and preserve cognitive performance during long-duration missions.