Bright light as a chronobiological countermeasure for shiftwork in space

Area of Science:

• Space Medicine
• Chronobiology
• Sleep Science

Background:

• Space missions disrupt astronaut sleep and circadian rhythms due to factors like shift work and altered light exposure.
• Bright light therapy is a potential tool for mitigating these circadian disruptions.

Purpose of the Study:

• To investigate the effectiveness of timed bright light exposure in accelerating adaptation to a 12-hour phase delay in simulated microgravity.
• To determine if light exposure timing influences the rate of circadian adjustment.

Main Methods:

• Four male subjects underwent simulated microgravity (bedrest) with a 12-hour wake extension.
• Subjects received bright light ( >3500 lux) for 5 hours daily under experimental (phase-advancing) and control (non-phase-advancing) conditions.
• Sleep, heart rate, body temperature, and urinary excretions were monitored.

Main Results:

• Only 6-hydroxymelatoninsulphate and potassium excretion rhythms showed significantly faster adjustment under the experimental bright light condition.
• Different circadian rhythms adapted at varying rates, similar to time zone shifts.
• Sleep duration was shorter in simulated microgravity compared to ambulatory conditions.

Conclusions:

• Bright light exposure can accelerate adjustment to work-rest schedule delays, but its effectiveness appears independent of the timing relative to the circadian temperature minimum.
• Circadian rhythm adaptation rates vary, and sleep is compromised in simulated microgravity.