Linked from
The 20 pages that link to Seasonal affective disorder, each with the reason it gives.
Circadian rhythmRelated: Seasonal light changes can alter circadian timing alongside mood and sleep.
PhotoperiodismRelated: Short winter days are associated with seasonal changes in mood and sleep.
SeasonsRelated: Reduced winter daylight is associated with this recurring seasonal mood pattern.
Day lengthRelated: Short winter days are associated with seasonal patterns of mood and symptoms.
WinterRelated: Reduced winter daylight is associated with this recurring mood disorder.