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Winter Depression Research Clinic


To study the pathophysiology of seasonal mood changes and to develop new more effective and efficient treatments.

For information about treatment please click on the links to the left.

What is Seasonal Affective Disorder (“SAD”)?

Seasonal Affective Disorder, also called SAD or winter depression, is a syndrome described by Norman Rosenthal and his colleagues in 1984. These investigators placed an ad in the newspaper seeking individuals who experienced worse mood seasonally. To their surprise, many responses were received, and it became clear that SAD was significantly common. The investigators also found that many patients improved with treatment with bright light, as discussed further below.

People with SAD experience changes in their mood, energy, sleep, weight, and appetite during the winter. Typically these changes begin in fall, reach their worst in December through February, and improve in the spring. Some individuals report changes as early as September, while others report changes beginning later in the fall. Similarly, some find that their symptoms have improved by early spring, while others find that symptoms continue until late spring. Some patients with SAD report their mood worsens with a series of dark days even in the summertime.

Signs and Symptoms of Winter Depression

The symptoms of SAD include depressed mood or sadness, decreased interest and enjoyment of activities, poor energy or severe fatigue, and decreased self-esteem. There may be changes in sleep, which may include insomnia (decreased sleep, such as trouble falling asleep, difficulty sleeping restfully, or waking up too early in the morning) or frequently hypersomnia (increased sleep: falling asleep early in the evening, sleeping to later hours in the morning, or long naps during the day). There may also be changes in appetite and weight, which may be decreased or more frequently increased. Some individuals with SAD experience cravings for carbohydrates such as bread or pasta, or other “comfort foods.” These are all symptoms of clinical depression (“Major Depression”). SAD is a form of clinical depression, but it is notable that fatigue, increased sleep, and increased appetite and weight are often the most prominent symptoms.

During the winter, bears hibernate: they eat a lot and then sleep through the winter. It seems that some humans experience the symptoms of “hibernation” in the winter.

There are a small group of patients who have worse mood in the summer, but less is known about “summer depression.”

Who is Likely to Have SAD?

SAD is more common in latitudes further from the equator. Within the United States, SAD is rare in Florida, more common in Mid-Atlantic States, and most common in the northern US or Canada. One study using questionnaires estimated an incidence of SAD of 1% in Florida, around 5% at the latitude of New York, and around 10% at the latitude of New Hampshire. Some patients report that they did not have trouble with the winter when they lived in southerly latitudes but did have significant seasonal symptoms when they moved further north.

SAD is clearly more common in women than men. Most estimates suggest than SAD is 2 to 4 times more common in women than men. It is not known why this is so. It appears that women with SAD are more likely to have premenstrual mood changes, and women with greater premenstrual mood changes are more likely to have SAD.

SAD typically begins in young adulthood, and then continues through adult life. Some patients report having problems in wintertime that began in child or teenage years, while other patients report seasonal symptoms began in their 30s, 40s, or later.

Doesn't Everyone Have SAD? What is Subsyndromal SAD?

When questionnaires are distributed to samples of people at large, about 90% of individuals report changes in energy, mood, sleep, appetite, and/or weight in the winter. Seasonal changes are normal in human beings living away from the equator. Nature seems to have intended human beings to slow down in the winter season.

Some individuals have seasonal changes that do not meet the full diagnostic criteria for SAD, but these changes are severe enough that the individual might seek treatment. Such conditions are called “subsyndromal SAD.” In our clinic, we sometimes saw patients who suffered from fatigue or increased appetite or other symptom, but did not have all of the symptoms of clinical depression. Fortunately, treatments for SAD are often helpful in subsyndromal SAD.

Who Does Not Have SAD?

Individuals with SAD have episodes of depression virtually every winter and are fully back to their normal selves in the summer. Individuals with SAD may have had an episode of depression outside the winter, but the number of seasonal episodes greatly outnumber non-seasonal episodes. If you do not have a clear seasonal pattern of depression in the winter with full recovery in the summer, then you do not have SAD.

Some individuals with recurrent depression or bipolar disorder seem to have a greater likelihood of having clinical depression in the fall or winter. In our clinical experience, some of these individuals may benefit significantly from bright light treatment, just like patients with SAD. Current research also suggests that some individuals with clinical depression with no seasonal pattern might benefit from bright light treatment too: this is an active area of study.

Yale Faculty

Paul Desan, MD, PhD