Carbon monoxide: a critical physiological regulator sensitive to light.

Area of Science:

• Biochemistry
• Physiology
• Chronobiology

Background:

• The mechanism of therapeutic light absorption in seasonal and nonseasonal depression remains unclear.
• Carbon monoxide (CO), a blood-borne gasotransmitter, is a potential mediator of bright-light therapy's effects.

Purpose of the Study:

• To investigate whether bright light exposure increases carbon monoxide (CO) concentrations in human blood.
• To explore the potential role of CO in the physiological regulation of circadian rhythms and the antidepressant effects of light therapy.

Main Methods:

• Peripheral blood samples from healthy female volunteers were analyzed for CO concentrations.
• Samples were exposed in vitro to darkness versus bright white light (10,000 lux) for 2 hours.
• Gas chromatography was used to measure CO concentrations in blood samples.

Main Results:

• Bright white light exposure significantly increased blood CO concentrations compared to darkness (p < 0.0001 in the first study, p < 0.02 in the confirmatory study).
• Time of day was inversely associated with the increase in CO concentration under bright light, suggesting a stronger effect in the morning.
• The findings were consistent across two independent studies with different participant groups.

Conclusions:

• Bright light exposure robustly increases human blood CO levels in vitro.
• This supports the hypothesis that CO acts as a physiological regulator of circadian rhythms.
• The findings provide human evidence for CO's role in light's antidepressant effects, replicating preclinical data.