Seasonal affective disorder (SAD), also known as winter depression, winter blues, summer depression, summertime sadness, or seasonal depression, is a mood disorder subset in which people who has normal mental health throughout most of the year experience depressive symptoms in the winter or summer.
SAD becomes depressed in the winter, because of a phase delay in circadiacrhythms relative to the sleep/wake cycle. Seasonal mood symptoms suggest that genetic aberrations may underlie the various abnormalities, which cause SAD symptoms. Melatonin secretion occurs later in the night, Feel sad, grumpy, moody, or anxious, Lose interest in your usual activities, Eat more and crave carbohydrates, such as bread and pasta, Gain weight, Sleep more but still feel tired, Have trouble concentrating.
The prevalence estimates of SAD across 30 retrospective studies varied from 0% to 6.9%. All prospective population studies, except one, find seasonal variations in mood, depressive symptoms usually peaking in winter. SAD was more prevalent at higher northern latitudes, but the prevalence varied across ethnic groups. SAD has also been identified in children and adolescents. Seasonal exacerbations and remissions are not limited to mood disorders; it has also been found in bulimia nervosa, anxiety disorders and other psychiatric illnesses