The following test of the circadian phase-shift hypothesis for patients with winter depression (seasonal affective disorder, or SAD) uses low-dose melatonin administration in the morning or afternoon͞evening to induce phase delays or phase advances, respectively, without causing sleepiness. Correlations between depression ratings and circadian phase revealed a therapeutic window for optimal alignment of circadian rhythms that also appears to be useful for phase-typing SAD patients for the purpose of administering treatment at the correct time. These analyses also provide estimates of the circadian component of SAD that may apply to the antidepressant mechanism of action of appropriately timed bright light exposure, the treatment of choice. SAD may be the first psychiatric disorder in which a physiological marker correlates with symptom severity before, and in the course of, treatment in the same patients. The findings support the phaseshift hypothesis for SAD, as well as suggest a way to assess the circadian component of other psychiatric, sleep, and chronobiologic disorders.chronobiology ͉ circadian rhythms ͉ melatonin ͉ seasonal affective disorder ͉ dim light melatonin onset (DLMO)

Melatonin's timekeeping function is undoubtedly related to the fact that it is primarily produced during nighttime darkness; that is, melatonin and light occur at opposite times. The human phase response curve (PRC) to melatonin appears to be about 12h out of phase with the PRC to light. These striking complementarities, together with light's acute suppressant effect on melatonin production, suggest that a function for endogenous melatonin is to augment entrainment of the circadian pacemaker by the light-dark cycle. The melatonin PRC also indicates correct administration times for using exogenous melatonin to treat circadian phase disorders.

These results should help establish the importance of circadian (morning or evening) time of light exposure in the treatment of winter depression. We recommend that bright-light exposure be scheduled immediately on awakening in the treatment of most patients with seasonal affective disorder.

No abstract

Good-quality evidence suggests that behavioral counseling interventions with multiple sessions conducted in STI clinics and primary care effectively reduces STI incidence in "at-risk" adult and adolescent populations. Additional trial evidence is needed for both lower-intensity behavioral counseling interventions and lower-risk patient populations.