Seasonal Affective Disorder (SAD) Overview: Types, Causes and Risk Factors

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An Overview of Seasonal Affective Disorder

Depression that occurs at the same time every year is known as SAD with symptoms typically beginning in September/October and ending in April/May; this is also known as winter depression.

Although rare, some people experience summer depression, a type of SAD that occurs in the spring or summer. The warmer months may also trigger reverse seasonal affective disorder, a condition related to bipolar disorder.

Seasonal Affective Disorder: Decreased Daylight, Melatonin and Serotonin

There is no one definitive cause. Regarding winter depression, anecdotal evidence suggests decreased daylight is responsible for disrupting the body’s circadian rhythms, such as body temperature and sleep-wake cycle, and adversely affecting serotonin and melatonin levels.

Without adequate light, the body is unable to produce sufficient levels of serotonin, which can lead to depression. Melatonin is produced when daylight subsides, encouraging sleep. Decreased light during the colder months forces an untimely production of melatonin, which is believed to be responsible for the fatigue and sleepiness felt by many people with SAD.

By way of contrast summer depression may be related to too much sunlight and increased temperatures.

Symptoms Identifying Winter Depression, Summer Depression and Reverse SAD

Symptoms differ amongst the three types of SADs, each with its own set of characteristics. They are generally temporary, lasting through the given season:

Winter Depression

Feelings of anxiousness, irritability and hopelessness, overly fatigued and sleepy, possible weight gain and increased appetite for carbohydrates, social withdrawal, decreased energy, and increased loss of interest in daily activities often mimicking general depression.

Summer Depression

Summer-related depression is often marked by poor appetite and weight loss, insomnia, feelings of irritability, agitation and anxiousness, and an increased sex drive.

Reverse SAD

Brought on by spring/summer, this form of bipolar is characterized by heightened enthusiasm, feelings of elation, racing thoughts, and hyperactivity.

Seasonal Affective Disorder Risk Factors

Certain factors place individuals at increased risk of developing SAD: gender, geographic location and genetics. More women than men suffer from SAD; however, men appear to suffer from intense severe symptoms. Children and teens are not exempt from SAD; in fact, SAD may develop at this early stage of life and carry through to adulthood. People living further north or south of the equator are more prone to SAD due to the lack of daylight in the winter and lengthy summer days.

A family history of SAD may play a role since genetic loading “is similar for seasonal and nonseasonal mood disorders,” according to Depression Symptoms and Family History in Seasonal and Nonseasonal Mood Disorders, a study by the Department of Psychiatry at the University of British Columbia and published in the American Journal of Psychiatry.

NB: This article is for information purposes only and is not intended to replace sound medical advice and opinion.


Mayo Clinic website. “Seasonal affective disorder (SAD)”,

MedlinePlus website. “Seasonal affective disorder”,

National Center for Biotechnology Information, U.S. National Library of Medicine website. “Seasonal affective disorder”,

WebMD website. “Seasonal affective disorder (SAD) – Topic Overview”,

National Center for Biotechnology Information, U.S. National Library of Medicine website. “Depression symptoms and family history in seasonal and nonseasonal mood disorders”,

American Journal of Psychiatry website. “Seasonal affective disorder with summer depression and winter hypomania”,