What is a defining characteristic of seasonal affective disorder?

Seasonal affective disorder (SAD) is primarily characterized by its relationship to seasonal changes, specifically in how symptoms of depression typically manifest during a specific time of year—most often in the winter months when there is less natural sunlight. The defining feature of SAD is that individuals experience significant mood changes, typically depressive episodes that correlate with the seasons; symptoms may improve with the arrival of spring and summer, and worsen again as autumn approaches.

This characteristic highlights the impact of environmental factors, particularly changes in daylight, on mood regulation. In contrast, the other options do not accurately capture the nature of SAD. For instance, while it can affect individuals of various ages, it does not exclusively target elderly individuals. Moreover, depressive episodes in seasonal affective disorder are not consistent throughout the year but are distinctly tied to the seasonal cycle. Bipolar disorder can involve manic episodes, particularly in certain types, but seasonal affective disorder does not typically lead to manic episodes during the summer; instead, it primarily involves depressive symptoms influenced by changes in light.