Seasonal Affective Disorder
WHAT IS SAD? What are the links between light and seasonal depression? Seasonal Affective Disorder (SAD) is a specific type of recurring depressive illness that manifests in an annual pattern, usually from early-to-late fall and subsiding with the longer, sunnier days of spring. Some people have the milder form, called Subsyndromal-SAD (S-SAD), also called Winter Blues, which causes minor problems in their lives but not the total disruption that full-blown SAD causes.
This is the Winter-SAD subtype; another subtype is Summer-SAD, which occurs in the spring & summer months. Summer-SAD is much rarer than Winter-SAD, is less well researched, and its cause is undetermined. Throughout this website, unless otherwise noted, the term "SAD" refers specifically to Winter-SAD. The two share a distinct link between changes in natural light and seasonal depression, however.