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 th e symptoms of some psychiatric disorders. A recent report suggested that sk in light exposure cart 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 suppre ss the pinenl melatonin secretion or decrease serum total bilirubin in cond itions 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 far six subjects and 3000-lux, 15 W/m(2) blue light for one sub ject). Hourly blood samples were collected from 7:00 PM to 7:00 AM for mela tonin 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 collect ed from 7:00 PM to 11:00 PM and from 11:00 PM to 7:00 AM. Results: The skirt light exposure did not cause any significant changes in serum melatonin or bilirubin levels. The excretion of bilirubin in urine wa s also the same in both sessions. Conclusions: Significant melatonin suppression by extraocular light does no t 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. (C) 2000 Society of Biological Psychiatry.