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 .
Effects of tryptophan depletion on drug-free patients with seasonal affective disorder during a stable response to bright light therapy.
BACKGROUND A dysfunction of the serotonin system may play a major role in the pathogenesis of seasonal affective disorder .  Bright light therapy has been shown to be effective in the treatment of winter depression in patients with seasonal affective disorder .  Light therapy-induced remission from depression may be associated with changes in brain serotonin function . METHODS After at least 2 weeks of clinical remission , 12 drug-free patients who had had depression with seasonal affective disorder underwent tryptophan depletion in a double-blind , placebo-controlled , balanced cross-over design study . RESULTS Short-term tryptophan depletion induced a significant decrease in plasma free and total tryptophan levels ( P < .001 for both , repeated measures analysis of variance ) , with peak effects occurring 5 hours after ingestion of a tryptophan-free amino acid drink . It emerged that tryptophan depletion leads to a transient depressive relapse , which was most pronounced on the day after the tryptophan-depletion testing . No clinical ly relevant mood changes were observed in the control testing . CONCLUSIONS The maintenance of light therapy-induced remission from depression in patients with seasonal mood cycles seems to depend on the functional integrity of the brain serotonin system . Our results suggest that the serotonin system might be involved in the mechanism of action of light therapy
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 .