Which factor most contributes to circadian disruption during irregular schedules?

• A. Global warming
• B. Dehydration during flight
• C. Poor sleep environment
• D. Light exposure at inappropriate times

Answer: (D)

Light cues are the main driver of the body’s 24-hour clock. The brain’s master clock, in the suprachiasmatic nucleus, uses light information from the eyes to set when we feel awake and when we feel sleepy. When schedules are irregular, light is encountered at odd times—bright light during the biological night or insufficient light during the usual daytime. This mis-timing shifts the clock: evening light tends to delay the rhythm, while morning light tends to advance it. Repeated exposure to light at inappropriate times disrupts the alignment between your internal clock and the external day-night cycle, leading to circadian disruption, sleepiness at inappropriate times, and poorer performance.

Other factors like dehydration or a less optimal sleep environment can affect how well you sleep, but they don’t reset the internal clock in the same timing-sensitive way. Global warming isn’t a direct driver of circadian timing either.