Bright light exposure of a large skin area does not affect melatonin or bilirubin levels in humans.
BACKGROUND
Light treatment through the eyes is effective in alleviating the symptoms of some psychiatric disorders. A recent report suggested that skin light exposure can affect human circadian rhythms. Bilirubin can serve as a hypothetical blood-borne mediator of skin illumination into the brain. We studied whether bright light directed to a large body area could suppress the pineal melatonin secretion or decrease serum total bilirubin in conditions that could be used for therapeutic purposes.


METHODS
Seven healthy volunteers participated in two consecutive overnight sessions that were identical except for a light exposure on the chest and abdomen in the second night from 12:00 AM to 6:00 AM (10,000-lux, 32 W/m(2) cool white for six subjects and 3000-lux, 15 W/m(2) blue light for one subject). Hourly blood samples were collected from 7:00 PM to 7:00 AM for melatonin radioimmunoassays. Bilirubin was measured by a modified diazo method in blood samples taken at 12:00 AM and 6:00 AM and in urine samples collected from 7:00 PM to 11:00 PM and from 11:00 PM to 7:00 AM.


RESULTS
The skin light exposure did not cause any significant changes in serum melatonin or bilirubin levels. The excretion of bilirubin in urine was also the same in both sessions.


CONCLUSIONS
Significant melatonin suppression by extraocular light does not occur in humans. Robust concentration changes of serum total bilirubin do not have a role in mediating light information from the skin to the central nervous system.
Lindblom
N
N
Pediatric Neurology, Hospital for Children and Adolescents, University of Helsinki, Helsinki, Finland.
Hätönen
T
T
Laakso
M
M
Alila-Johansson
A
A
Laipio
M
M
Turpeinen
U
U
D000005:Abdomen; D000328:Adult; D000704:Analysis of Variance; D001663:Bilirubin / Q000097:blood* / Q000652:urine; D018592:Cross-Over Studies; D005260:Female; D006801:Humans; D007118:Immunoassay; D008297:Male; D008550:Melatonin / Q000097:blood*; D010789:Phototherapy; D012879:Skin Physiological Phenomena; D013909:Thorax; D014785:Vision, Ocular
D008550:Melatonin; D001663:Bilirubin