Effects of light on low nocturnal bilirubin in winter depression: a preliminary report

Background: The light-absorbing pigments involved in the induction of treatment of winter depression are unknown. It has been proposed that circulating bilirubin serves as a photoreceptor, in part because of its similarity to the chromophore of phytochrome, a primary time-setting plant molecule. Methods: We measured nocturnal bilirubin levels in nine patients with winter depression, and seven age- and gender-matched normal comparison volunteers. Results: Nocturnal bilirubin levels were lower in patients than in controls (p <.02), increased in both groups during the night (p <.0001), and increased in patients after 2 weeks of morning light treatment (p = .0009), which was accompanied by clinical improvement. Conclusions: Low nocturnal bilirubin levels may be associated with winter seasonal depression.