Recent systematic review s have shown that  light therapy  is an efficacious and well-tolerated treatment for SAD .
There is also evidence for efficacy of pharmacotherapy to treat and prevent SAD .
SAD is a common condition with significant psychosocial impairment .
BACKGROUND Seasonal affective disorder ( SAD ) consists of recurrent major depressive episodes in the fall/winter with remissions in spring/summer .
RESULTS A careful history is important to make the diagnosis and differentiate SAD from other similar conditions such as subsyndromal SAD and atypical depression .
Seasonal patterns with winter worsening are also recognized in " nonseasonal " depression as well as many other psychiatric conditions , and comorbidity with SAD is common .
The pathophysiology of SAD seems to be heterogeneous as research on circadian , neurotransmitter function and genetic hypotheses have shown discrepant results .
A dual vulnerability model with differential loading on separate seasonal and depression factors has been proposed to explain these findings .
The Impact of Latitude on the Prevalence of Seasonal Depression
Background : This study sought to determine whether the prevalence of the seasonal subtype of major depression ( SAD ) in the community varied as a function of latitude . Methods : R and om telephone numbers were generated across 8 degrees of latitude ( 41.5 ° N to 49.5 ° N ) for the province of Ontario . Eight strata of 1 degree each were sample d equally throughout a 12-month period . Using a vali date d and structured diagnostic interview , we interviewed by telephone  respondents over 20 years of age who had lived in the region for 3 years or more . We evaluated patterns of symptom change across seasons to establish a diagnosis of SAD according to DSM-IV criteria . Results : Of the 2078 households that were assessed for eligibility , 1605 ( 77 % ) completed the interview . The crude prevalence of lifetime SAD was 2.6 % ( 95 % CI , 1.9 to 3.5 ) . There was no impact of latitude on prevalence of either major depression or the seasonal subtype across the 8 strata , although the global measure of the severity of seasonal change in mood was significantly negatively correlated with latitude . Conclusions : SAD is a common subtype of major depression in Ontario , but there is no evidence to support an increase in prevalence with increasing latitude . Context e : Cette étude visait à déterminer si la prévalence du caractère saisonnier de la dépression majeure ( DMS ) dans la communauté variait selon la latitude . Méthodes : Des numéros de téléphone aléatoires ont été fournis sur 8 degrés de latitude ( de 41,5 ° N. à 49,5 ° N. ) dans la province de l'Ontario . Huit b and es de 1 degré chacune ont été échantillonnées également sur une période de 12 mois . À l'aide d'une entrevue diagnostique validée et structurée , nous avons interviewé par téléphone des répondants âgés de plus de 20 ans qui habitaient la région depuis 3 ans ou plus . Nous avons évalué les changements des modèles de symptômes selon les saisons pour établir un diagnostic de DMS selon les critères du DSM-IV . Résultats : Sur les 2 078 ménages admissibles , 1 605 ( 77 % ) ont terminé l'entrevue . La prévalence brute de la DMS à vie était de 2,6 % ( 95 % IC , 1,9 à 3,5 ) . La latitude n'influait pas sur la prévalence de la dépression majeure ou du caractère saisonnier dans les 8 b and es , bien que la mesure globale de la sévérité du changement saisonnier de l'humeur ait indiqué une corrélation négative significative à la latitude . Conclusions : La dépression majeure saisonnière est un sous-type rép and u de la dépression majeure en Ontario , mais aucune preuve ne soutient une augmentation de la prévalence parallèle à l'accroissement de la latitude
Recent systematic review s have shown that  light therapy  is an efficacious and well-tolerated treatment for SAD .
There is also evidence for efficacy of pharmacotherapy to treat and prevent SAD .
SAD is a common condition with significant psychosocial impairment .
BACKGROUND Seasonal affective disorder ( SAD ) consists of recurrent major depressive episodes in the fall/winter with remissions in spring/summer .
RESULTS A careful history is important to make the diagnosis and differentiate SAD from other similar conditions such as subsyndromal SAD and atypical depression .
Seasonal patterns with winter worsening are also recognized in " nonseasonal " depression as well as many other psychiatric conditions , and comorbidity with SAD is common .
The pathophysiology of SAD seems to be heterogeneous as research on circadian , neurotransmitter function and genetic hypotheses have shown discrepant results .
A dual vulnerability model with differential loading on separate seasonal and depression factors has been proposed to explain these findings .