Seasonal depression, also known as seasonal affective disorder (SAD), is a type of depression that is associated with seasons, particularly late fall and the entire winter season. Shorter days, colder temperatures, and less exposure to light have been shown to change our sleep/wake patterns and throw off our “internal clocks” affecting our levels of melatonin, serotonin, and vitamin D.
Individuals with seasonal depression must meet the criteria for major depressive disorder with symptoms coinciding with the specific seasons and lasting for at least two years.
Individuals who live further from the Equator are more at risk for developing seasonal depression compared to individuals who live closer to the Equator. One percent of individuals who live in Florida have SAD, whereas nine percent of individuals who live in Alaska have SAD. Females are more at risk of developing SAD compared to males, and individuals who have a history of depression or bipolar disorder are also at an increased risk for developing SAD.