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 .
Epidemiological findings of seasonal changes in mood and behavior. A telephone survey of Montgomery County, Maryland.
Patterns of seasonal changes in  mood and behavior in Montgomery County , Maryl and , were evaluated in r and omly selected household sample s by lay interviewers using a telephone version of the Seasonal Pattern Assessment Question naire . The method for selecting the sample unit was r and om-digit dialing . We found that 92 % of the survey subjects noticed seasonal changes of mood and behavior to varying degrees . For 27 % of the sample seasonal changes were a problem and 4.3 % to 10 % of subjects , depending on the case-finding definition , rated a degree of seasonal impairment equivalent to that of patients with seasonal affective disorder . The seasonal pattern of " feeling worst " exhibited a bimodal distribution with a greater winter and a substantially lower summer peak ( ratio , 4.5:1 ) . Younger women who have a problem with seasonal changes and who feel worse on short days tended to exhibit the highest seasonality scores . It is apparent from our study that seasonal affective disorder represents the extreme end of the spectrum of seasonality that affects a large percentage of the general population . The influence of environmental factors on mood disorders and mood changes in the general population might provide valuable insight into pathogenesis , treatment , and prevention of affective illness
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 .