Seasonal affective disorder (SAD), also known as winter depression or winter blues, is a mood disorder in which people who have normal mental health throughout most of the year, experience depressive symptoms in the winter or, less frequently, in the summer, spring or autumn, repeatedly, 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".
Once regarded skeptically by the experts, seasonal affective disorder is now well established. Epidemiological studies estimate that its prevalence in the adult population of the US ranges from 1.4 percent (Florida) to 9.7 percent (New Hampshire).
The US 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 is often referred to as reverse seasonal affective disorder, and can also include heightened anxiety.
There are many different treatments for classic (winter-based) seasonal affective disorder, including light therapy with sunlight or bright lights, antidepressant medication, cognitive-behavioral therapy, ionized-air administration, and carefully timed supplementation of the hormone melatonin.
Symptoms of SAD may consist of difficulty waking up in the morning, morning sickness, tendency to oversleep as well as to overeat, and especially a craving for carbohydrates, which leads to weight gain. Other symptoms include a lack of energy, difficulty concentrating on completing tasks, and withdrawal from friends, family, and social activities. All of this leads to the depression, pessimistic feelings of hopelessness, and lack of pleasure which characterize a person suffering from this disorder.
People who experience summer SAD (spring and summer depression) show symptoms of classic depression including insomnia, anxiety, irritability, decreased appetite, weight loss, social withdrawal, and a decreased sex drive. Additionally, many patients are unable to cope with the increased temperatures during spring and summer.
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. SAD is measurably present at latitudes in the Arctic region, such as Finland (64º 00´N) where the rate of SAD is 9.5%. Cloud cover may contribute to the negative effects of SAD.
The symptoms of SAD mimic those of dysthymia or even major depressive disorder. There is also potential risk of suicide in some patients experiencing SAD. One study reports 6-35% of sufferers required hospitalization during one period of illness. At times, patients may not feel depressed, but rather lack energy to perform everyday activities.
Various proximate causes have been proposed. One possibility is that SAD is related to a lack of serotonin, and serotonin polymorphisms could play a role in SAD, although this has been disputed. Mice incapable of turning serotonin into N-acetylserotonin (by Serotonin N-acetyltransferase) appear to express "depression-like" behavior, and antidepressants such as fluoxetine increase the amount of the enzyme Serotonin N-acetyltransferase, resulting in an antidepressant-like effect. 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, via the retinohypothalamic tract and the suprachiasmatic nucleus, 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.
SAD was first systematically reported and named in the early 1980s by Norman E. Rosenthal, M.D., and his associates at the National Institute of Mental Health (NIMH). Rosenthal was initially motivated by his desire to discover the cause of his own experience of depression during the dark days of the northern US winter. He theorized that the lesser amount of light in winter was the cause. Rosenthal and his colleagues then documented the phenomenon of SAD in a placebo-controlled study utilizing light therapy. A paper based on this research was published in 1984. Although Rosenthal's ideas were initially greeted with skepticism, SAD has become well recognized, and his 1993 book, Winter Blues has become the standard introduction to the subject.
Research on SAD in the United States began in 1970 when Herb Kern, a research engineer, had also noticed that he felt depressed during the winter months. Kern suspected that scarcer light in winter was the cause and discussed the idea with scientists at the NIMH who were working on bodily rhythms. They were intrigued, and responded by devising a lightbox to treat Kern’s depression. Kern felt much better within a few days of treatments, as did other patients treated in the same way.
In many species, activity is diminished during the winter months in response to the reduction in available food and the difficulties of surviving in cold weather. Hibernation is an extreme example, but even species that do not hibernate often exhibit changes in behavior during the winter. It has been argued that SAD is an evolved adaptation in humans that is a variant or remnant of a hibernation response in some remote ancestor. Presumably, food was scarce during most of human prehistory, and a tendency toward low mood during the winter months would have been adaptive by reducing the need for calorie intake. The preponderance of women with SAD suggests that the response may also somehow regulate reproduction.
There are many different treatments for classic (winter-based) seasonal affective disorder, including light therapy, medication, ionized-air administration, cognitive-behavioral therapy and carefully timed supplementation of the hormone melatonin.
Photoperiod-related alterations of the duration of melatonin secretion may affect the seasonal mood cycles of SAD. This suggests that light therapy may be an effective treatment for SAD. 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 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. A 1995 study showed that green light therapy at doses of 350 lux produces melatonin suppression and phase shifts equivalent to 10,000 lux bright light therapy in winter depressives. A study published in May 2010 suggests that the blue light often used for SAD treatment should perhaps be replaced by green or white illumination. Discovering the best schedule is essential. One study has shown that up to 69% of patients find lightbox treatment inconvenient and as many as 19% stop use because of this.
Dawn simulation has also proven to be effective; in some studies, there is an 83% better response when compared to other bright light therapy. When compared in a study to negative air ionization, bright light was shown to be 57% effective vs. dawn stimulation 50%. 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 can also consist of exposure to sunlight, either by spending more time outside or using a computer-controlled heliostat to reflect sunlight into the windows of a home or office.
SSRI (selective serotonin reuptake inhibitor) antidepressants have proven effective in treating SAD. Bupropion is also effective as a prophylactic. Effective antidepressants are fluoxetine, sertraline, or paroxetine. Both fluoxetine and light therapy are 67% effective in treating SAD according to direct head-to-head trials conducted during the 2006 Can-SAD study. Subjects using the light therapy protocol showed earlier clinical improvement, generally within one week of beginning the clinical treatment.
Negative air ionization, which involves releasing charged particles into the sleep environment, has been found effective with a 47.9% improvement if the negative ions are in sufficient density (quantity). Depending upon the patient, one treatment (e.g., lightbox) may be used in conjunction with another (e.g., medication).
Alfred J. Lewy of Oregon Health & Science University and others see the cause of SAD as a misalignment of the sleep-wake phase with the body clock, circadian rhythms out of synch, and treat it with melatonin in the afternoon. Correctly timed melatonin administration shifts the rhythms of several hormones en bloc.
Another explanation is that vitamin D levels are too low when people do not get enough Ultraviolet-B on their skin. An alternative to using bright lights is to take vitamin D supplements. However, one study did not show a link between vitamin D levels and depressive symptoms in elderly Chinese.
Winter depression is a common slump in the mood of some inhabitants of most of the Nordic countries. It was first described by the 6th century Goth scholar Jordanes in his Getica wherein he described the inhabitants of Scandza (Scandinavia). Iceland, however, seems to be an exception. A study of more than 2000 people there found the prevalence of seasonal affective disorder and seasonal changes in anxiety and depression to be unexpectedly low in both sexes. The study's authors suggested that propensity for SAD may differ due to some genetic factor within the Icelandic population. A study of Canadians of wholly Icelandic descent also showed low levels of SAD. It has more recently been suggested that this may be attributed to the large amount of fish traditionally eaten by Icelandic people, 225 lb per person per year as opposed to about 50 lb in the US and Canada, rather than to genetics. Fish is high in vitamin D. Fish also contains docosahexaenoic acid (DHA), which has been shown to help with a variety of neurological dysfunction.
In the United States, a diagnosis of seasonal affective disorder was first proposed by Norman E. Rosenthal, MD in 1984. Rosenthal wondered why he became sluggish during the winter after moving from sunny South Africa to New York. He started experimenting increasing exposure to artificial light, and found this made a difference. In Alaska it has been established that there is a SAD rate of 8.9%, and an even greater rate of 24.9% for subsyndromal SAD.
Around 20% of Irish people are affected by SAD, according to a survey conducted in 2007. The survey also shows women are more likely to be affected by SAD than men. An estimated 10% of the population in the Netherlands suffer from SAD.
SAD and bipolar disorder
Most people with SAD experience major depressive disorder, but as many as 20% may have or may go on to develop a bipolar disorder (manic-depressive disorder). It is important to discriminate the improved mood associated with recovery from the winter depression and a manic episode because there are important treatment differences. In these cases, people with SAD may experience depression during the winter and hypomania in the summer.
- Circadian rhythm sleep disorder
- Depression (mood)
- Risks and benefits of sun exposure
- Social anxiety disorder
- Vitamin D
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