Seasonal Affective Disorder (SAD) is defined as a type of depression that is related to the change of the seasons. About 5% of Americans have been diagnosed with SAD with a range from 1.9% in Florida and 9.9% in Alaska. For most people, the SAD symptoms begin to develop from the start of fall and into the winter months. However, SAD can also be found, albeit far less frequently, in the spring and summer.

A few symptoms separate fall and winter Seasonal Affective Disorder from the spring and summer variant. Fall and winter SAD are associated with irritability, low energy, oversleeping, and weight gain. For spring and summer SAD symptoms include insomnia, weight loss, anxiety, and poor appetite. Both forms’ symptoms can be enhanced in people who have been diagnosed with another form of depression or bipolar disorder. 

 There are few main causes of Seasonal Affective Disorder. The first is a lack sunlight can disrupt your circadian rhythm or your biological clock. The reduced sunlight in the fall and winter may cause winter-onset SAD because the lack of sunlight may disrupt your body’s internal clock and lead to feeling of depression. Another cause is reduced serotonin levels, a brain chemical that affects mood, which can be caused by the lack of sunlight and may trigger depression. A third cause is melatonin levels, which changes in season can disrupt. Melatonin plays a role in sleep patterns and mood.

Several factors that may increase the risk of SAD. One is being female, women are diagnosed with Seasonal Affective Disorder more often than men, however men may have more severe symptoms. Another is how old you are as young people have a higher risk of winter SAD,  which is less common in older adults. Family history also plays an important role; people with SAD may be more likely to have blood relatives with this or another form of depression. How far a person lives from the equator can also increase the risk for developing SAD. The farther a person lives from the equator the more common Seasonal Affective Disorder is, likely due to the longer nights in the winter and the longer days in the summer.