What is Seasonal Affective Disorder?

Seasonal Affective Disorder, also known as S.A.D., is a mood disorder in which people who have normal mental health throughout most of the year experience depressive symptoms typically in the winter, spring, or autumn year after year. In the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), SAD is not a unique mood disorder, but is “a specifier of major depression.”

Although experts were initially skeptical, this condition is now recognized as a common disorder, with its prevalence in the U.S. ranging from 1.4% in Florida to 9.7% in New Hampshire. The U.S. National Library of Medicine notes that “some people experience a serious mood change when the seasons change. They may sleep too much, have little energy, and may also feel depressed. Though symptoms can be severe, they usually clear up.” The condition in the summer can include heightened anxiety.

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Symptoms of SAD may consist of difficulty waking up in the morning, morning sickness, tendency to oversleep and over eat, especially a craving for carbohydrates, which leads to weight gain. Other symptoms include a lack of energy, difficulty concentrating on or completing tasks, and withdrawal from friends, family, and social activities. This leads to depression, pessimistic feelings of hopelessness, and lack of pleasure which characterize a person suffering from this disorder.

People who experience spring and summer depression show symptoms of classic depression including insomnia, anxiety, irritability, decreased appetite, weight loss and social withdrawal.

Diagnostic Criteria

According to the American Psychiatric Association DSM-IV criteria, Seasonal Affective Disorder is not regarded as a separate disorder. It is called a “course specifier” and may be applied as an added description to the pattern of major depressive episodes in patients with major depressive disorder or patients with bipolar disorder. The “Seasonal Pattern Specifier” must meet four criteria: depressive episodes at a particular time of the year; remissions or mania/hypomania at a characteristic time of year; these patterns must have lasted two years with no nonseasonal major depressive episodes during that same period; and these seasonal depressive episodes outnumber other depressive episodes throughout the patient’s lifetime.

The Mayo Clinic describes three types of SAD, each with its own set of symptoms. In the popular culture, sometimes the term “seasonal affective disorder” is applied inaccurately to the normal shift to lower energy levels in winter, leading people to believe they have a physical problem that should be addressed with various therapies or drugs.


Seasonal mood variations are believed to be related to light. An argument for this view is the effectiveness of bright-light therapy. The symptoms of SAD mimic those of mild chronic depression or even major depressive disorder.

At times, patients may not feel depressed, but rather lack energy to perform everyday activities.   One possibility is that SAD is related to a lack of serotonin. Another theory is that the cause may be related to melatonin which is produced in dim light and darkness by the pineal gland since there are direct connections between the retina and the pineal gland.

Subsyndromal Seasonal Affective Disorder is a milder form of SAD experienced by an estimated 14.3% (vs. 6.1% SAD) of the U.S. population. The blue feeling experienced by both SAD and SSAD sufferers can usually be dampened or extinguished by exercise and increased outdoor activity, particularly on sunny days, resulting in increased solar exposure. Connections between human mood, as well as energy levels, and the seasons are well documented, even in healthy individuals.


There are many different treatments for classic (winter-based) seasonal affective disorder. Light therapy uses a lightbox which emits far more lumens than a customary incandescent lamp. Bright white “full spectrum” light at 10,000 lux, blue light at a wavelength of 480 nm at 2,500 lux or green (actually cyan or blue-green) light at a wavelength of 500 nm at 350 lux are used with the first-mentioned historically preferred.

Bright light therapy is effective with the patient sitting a prescribed distance, commonly 30–60 cm, in front of the box with her/his eyes open but not staring at the light source for 30–60 minutes. Discovering the best schedule is essential. Patients using light therapy can experience improvement during the first week, but increased results are evident when continued throughout several weeks. Most studies have found it effective without use year round but rather as a seasonal treatment lasting for several weeks until frequent light exposure is naturally obtained.

Light therapy has been used for over 20 years to treat SAD with numerous studies citing its effectiveness. It is recommended as a first-line treatment for SAD in Canadian, American, and international clinical guidelines.  The mood of individuals with SAD can improve with as little as 20 minutes of bright light exposure. Bright light is more effective than dim light in protecting against “mood lowering” which commonly occurs in SAD.

According to researchers, Seasonal Affective Disorder or SAD, affects up to twenty percent of the population.

Common symptoms of SAD are tiredness, sleeping more often, carbohydrate cravings and sadness or depression. During winter seasons, chemicals in the brain produce higher levels of melatonin, which in turn makes people feel more lethargic. Serotonin levels, which help regulate people’s moods, are lower in the winter months.

There are several treatment options for SAD. However, many experts highly recommend light therapy using a SAD light therapy unit. These light boxes provide 10,000 lux of illumination (10-25 times brighter than ordinary light) which act as forty minutes of outdoor sunlight.

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