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 .
Follow-up study of seasonal affective disorder in Switzerland.
Of 39 diagnosed Seasonal Affective Disorder ( SAD ) patients who were interviewed 2 - 5 years after participation in a light therapy trial , 10 continued to have recurrent  major depressive episodes  in winter , and 17 manifested sub-syndromal SAD ( 2 patients also had recurrent brief depression , seasonal type ) . 8 patients had recovered , and 4 had shifted in symptomatology . Thus , over a number of years , the clinical diagnosis changed for the better in 64 % of the patients , suggesting that SAD is not a prodromal form of a more chronic major affective disorder , and that light therapy ( and perhaps also light-oriented behaviour ) reduced the incidence and depth of subsequent depressive episodes . Further evidence for this was the large reduction in use of conventional antidepressant drugs ( from 17 to 1 ) during the follow-up period . Diagnosis of SAD was stable and reliable
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 .