Although researchers are not certain what causes seasonal affective disorder, they suspect that it has something to do with the hormone melatonin.
Melatonin is thought to play an active role in regulating the “internal body clock,” which dictates when humans feel like going to bed at night and getting up in the morning.
Although seasonal affective disorder is most common when light is low, it may occur in the spring, which is often called reverse or spring-onset SAD. Recent research also indicates that SAD has a genetic factor; about 29% of cases in the United States run in families.
Causes and symptoms
The body produces more melatonin at night than during the day, and scientists believe it helps people feel sleepy at nighttime. There is also more melatonin in the body during winter, when the days are shorter.
Some researchers believe that excessive melatonin release during winter in people with SAD may account for their feelings of drowsiness or depression.
One variation on this idea is that people’s internal clocks may become out of sync during winter with the light-dark cycle, leading to a long-term disruption in melatonin release. Another possible cause of SAD is that people may not adjust their habits to the season, or sleep more hours when it is darker, as would be natural.
Seasonal affective disorder, while not an official category of mental illness listed by the American Psychiatric Association, is estimated to affect 6% of the American population. Another 25 million Americans may have a mild form of SAD, sometimes called the “winter blues” or “winter blahs.”
The risk of SAD increases the further from the equator a person lives; one early study of SAD found a 1.4% incidence of the disorder among people living in Florida, compared with 9.7% among residents of New Hampshire. Other factors that influence the incidence and severity of SAD are sex and age.
Women are more likely than men to develop SAD, but men with the disorder are more severely depressed than most women who have it. SAD appears to decrease in severity with age; the elderly have milder SAD symptoms than adolescents.
Comparative studies indicate that the incidence of SAD in the United States and Canada is about twice as high as in European countries at the same latitudes north of the Equator. These findings suggest that cultural factors are also involved in the disorder.
The symptoms of SAD are similar to those of other forms of depression. People with SAD may feel sad, irritable, or tired, and may find themselves sleeping too much. They may also lose interest in normal or pleasurable activities (including sex), become withdrawn, crave carbohydrates, and gain weight.
Diagnosis
Doctors usually diagnose seasonal affective disorder based on the patient’s description of symptoms, including the time of year they occur.
There is also a diagnostic questionnaire called the Seasonal Pattern Assessment Questionnaire, or SPAQ, used in all Canadian university hospitals and widely used in the United States to assess SAD patients.
Treatment
The first-line treatment for seasonal affective disorder is light therapy (also known as phototherapy). The most commonly used phototherapy equipment is a portable lighting device known as a light box.
The box may be mounted upright to a wall or slanted downward toward a table. The patient sits in front of the box for a pre-prescribed period of time (anywhere from 15 minutes to several hours). Some patients with SAD undergo light therapy sessions two or three times daily, others only once.
The time of day and the number of times treatment is administered depend on the physical needs and lifestyle of the patient. Light therapy treatment for SAD typically begins in the fall as the days begin to shorten, and continues throughout the winter and possibly the early spring.
The light from a slanted light box is designed to fall on the table supporting the box, so patients may look down to read or do other sedentary activities during therapy.
Patients using an upright light box must face the light source (although they need not look directly into the light). The light sources in these light boxes typically range from 2,500 to 10,000 lux (in contrast, average indoor lighting is 300 to 500 lux; a sunny summer day is about 100,000 lux).
A recent British study suggests that dawn simulation, a form of light therapy in which the patient is exposed to white light of gradually increasing brightness (peaking at 250 lux after 90 min) may be even more effective in treating SAD than exposure to bright light. Dawn simulation is started around 4:30 or 5 o’clock in the morning while the patient is still asleep.
Patients with eye problems should see an ophthalmologist regularly both before and during light therapy. Because some UV rays are emitted by the light boxes used in phototherapy, patients taking photosensitizing medications and those who have sun-sensitive skin should consult with a health care professional before beginning treatment. Patients with medical conditions that make them sensitive to UV rays should also see a doctor before starting phototherapy.
Light therapy appears to be safe for most people. However, it can cause side effects of eyestrain, headaches, insomnia, fatigue, sunburn, and dry eyes and nose in some patients.
Most of these effects can be managed by adjusting the timing and duration of light therapy sessions. A strong sun block and eye and nose drops can alleviate the others.
Recently, researchers have begun testing whether people who do not completely respond to light therapy can benefit from tiny doses of the hormone melatonin to reset the body’s internal clock. Early results look promising, but the potential benefits must be confirmed in larger studies before this type of treatment becomes widely accepted.
Allopathic treatment
- Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine (Prozac), paroxetine (Paxil), and sertraline (Zoloft)
- Monoamine oxidase inhibitors (MAO inhibitors), such as phenelzine sulfate (Nardil) and tranylcypromine sulfate (Parnate)
- Lithium salts, such as lithium carbonate (Eskalith), often used in people with bipolar mood disorders, are often useful with SAD patients who also suffer from bipolar disorder (excessive mood swings; formerly known as manic depression)
A number of psychotherapy approaches are useful as well. Interpersonal psychotherapy helps patients recognize how their mood disorder and their interpersonal relationships interact. Cognitive-behavioral therapy explores how the patient’s view of the world may be affecting mood and outlook.
A new treatment for SAD that is still in the experimental phase as of 2001 is the use of high-density negative air ionization.
Expected results
Most patients with seasonal affective disorder respond to light therapy, dawn simulation, and/or antidepressant drugs. Others respond to sleeping more hours in a dark room.
Some researchers estimate that as much as 9.5 hours of sleep are important in winter months and that getting more sleep will increase the person’s levels of natural melatonin.
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