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 .
Estimated Prevalence of the Seasonal Subtype of Major Depression in a Canadian Community Sample
Objective : To examine estimates of lifetime prevalence of  seasonal affective disorder ( SAD ) in Toronto , Ontario . Method R and om telephone numbers were generated for the city of Toronto , and 781 respondents completed a telephone interview .  Trained nonphysician interviewers conducted all interviews , which involved structured questions for diagnosing major depression . Patterns of symptom change across seasons were evaluated to establish a diagnosis of SAD according to DSM-III-R criteria . Results Correcting for sex and age , the prevalence of SAD defined by DSM-III-R criteria was 2.9 % ( 95%CI , 1.7 % to 4.0 % ) , and the overall lifetime prevalence of major depression in the sample was 26.4 % ( 95%CI , 23.3 % to 29.4 % ) . Some subjects were contacted for a follow-up interview conducted in person ; the positive predictive value for the diagnosis of major depression for the telephone interview was 100 % , and the negative predictive value was 93 % . Conclusions The seasonal subtype of depression represents 11 % of all subjects with major depression , suggesting that SAD is a significant public health concern . The telephone interview demonstrated adequate reliability , indicating that it is appropriate for epidemiological surveys of this nature
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 .