What is seasonal affective disorder or SAD?

In seasonal affective disorder, depression takes a seasonal pattern. Sufferers tend to become depressed in the winter months and recover as spring approaches. The condition appears to be linked to the lack of sunlight in the winter (even a poor summer may trigger a low mood in those who are susceptible to SAD).

This form of depression is atypical in that it tends to be associated with weight gain and sleeping for longer than usual. In many ways, it is not unlike a form of hibernation, in which winter brings on a marked decrease in activity.

Seasonal affective disorder, and its milder variants, could affect up to 20% of the population.