Overall , both forms of preventive light therapy reduced the incidence of SAD numerically compared with no light therapy .
BACKGROUND Seasonal affective disorder ( SAD ) is a seasonal pattern of recurrent major depressive episodes that most commonly occurs during autumn or winter and remits in spring .
The prevalence of SAD ranges from 1.5 % to 9 % , depending on latitude .
The predictable seasonal aspect of SAD provides a promising opportunity for prevention .
This review - one of four review s on efficacy and safety of interventions to prevent SAD - focuses on light therapy as a preventive intervention .
Light therapy is a non-pharmacological treatment that exposes people to artificial light .
Mode of delivery ( e.g. visors , light boxes ) and form of light ( e.g. bright white light ) vary .
OBJECTIVES To assess the efficacy and safety of light therapy ( in comparison with no treatment , other types of light therapy , second-generation antidepressants , melatonin , agomelatine , psychological therapies , lifestyle interventions and negative ion generators ) in preventing SAD and improving patient-centred outcomes  among adults with a history of SAD .
Effects of morning phototherapy on circadian markers in seasonal affective disorder.
BACKGROUND The suppression of melatonin by light at 00.30 hours has been shown to be greater in winter than in summer on patients with seasonal affective disorder ( SAD ) but not in matched normal controls . METHOD In this study 12 patients with SAD and 12 matched normal controls were exposed to morning light therapy in the winter .  Melatonin profiles and sensitivity to light were measured before and after treatment . RESULTS The SAD but not the normal group showed a phase advance of melatonin rhythms in response to phototherapy . There was an association between phase position and phase shift in the SAD but not in the normal group . CONCLUSIONS There may be instability of circadian rhythms in SAD mediated by a high-amplitude phase response curve , rather than a fixed phase abnormality as had been previously suggested . This instability may be secondary to impaired serotoninergic function in the afferent pathways to the suprachiasmatic nuclei
Overall , both forms of preventive light therapy reduced the incidence of SAD numerically compared with no light therapy .
BACKGROUND Seasonal affective disorder ( SAD ) is a seasonal pattern of recurrent major depressive episodes that most commonly occurs during autumn or winter and remits in spring .
The prevalence of SAD ranges from 1.5 % to 9 % , depending on latitude .
The predictable seasonal aspect of SAD provides a promising opportunity for prevention .
This review - one of four review s on efficacy and safety of interventions to prevent SAD - focuses on light therapy as a preventive intervention .
Light therapy is a non-pharmacological treatment that exposes people to artificial light .
Mode of delivery ( e.g. visors , light boxes ) and form of light ( e.g. bright white light ) vary .
OBJECTIVES To assess the efficacy and safety of light therapy ( in comparison with no treatment , other types of light therapy , second-generation antidepressants , melatonin , agomelatine , psychological therapies , lifestyle interventions and negative ion generators ) in preventing SAD and improving patient-centred outcomes  among adults with a history of SAD .