Biology 202
2000 First Web Report
On Serendip

SAD symptoms are essentially the same as those of general clinical depression. However, the former follows a seasonal pattern, whereas the latter is unaffected by calendar cycles. The warning signs of SAD typically reveal themselves in late autumn and virtually disappear by mid-spring, as the temperature increases and the days reach their maximum length. A patient's behavior patterns must be observed for at least two successive season-changes to properly diagnose SAD. (3).

The number of people who suffer from SAD seems to be directly related to latitude. The results of an extensive medical survey administered to hundreds of thousands of North American participants in the early 1990s, showed that close to 20% of the general public complained of symptoms related to seasonal depression. When these data were analyzed by region, a clear trend emerged; in the southernmost states like Florida and Arizona, where the weather remains mild all year and daylight hours are consistently longer, less than 5% of the population was afflicted with SAD. By contrast, as much as 30% of residents in northern states locales like Seattle and Alaska, appeared to suffer from SAD. (7). It has also been determined that women, who are more susceptible to the disorder at the onset of puberty, experience SAD three times more frequently than men. (2).

While the cause and mechanisms of Seasonal Affective Disorder remain somewhat mysterious, researchers believe that it is related to the amount of melatonin produced in our bodies. Melatonin is a hormone produced in the pineal gland that causes drowsiness (and is directly related to hibernation cycles of other mammals). (5). Light enters the eyes and is conducted by the optic nerve to an area of the hypothalamus called the suprachiasmatic nucleus, which is responsible for regulating body temperature and circadian rhythms. During the day, when the retina is exposed to bright natural light, the suprachiasmatic nucleus inhibits the pineal gland's production of melatonin, maintaining wakefulness. In the evening when the light is dim, the S.N. signals the pineal gland to initiate melatonin-production, inducing sleepiness. (8). During regular 24-hour cycles that have distinct light-dark contrasts, the body's sleep clock runs evenly. But "on dull winter days, especially (when a person spends a lot of time) indoors, not enough light is received to trigger this waking-up process", (4). and the system becomes sluggish. This leads to a general decrease in energy and an increased desire to sleep.

Recent evidence has also linked light exposure to the production of the neurotransmitter serotonin, which is thought to influence mood. People who are affected by SAD appear to have difficulty regulating serotonin levels in their blood. That these levels can be increased by a diet rich in carbohydrates explains the intense carbohydrate cravings of many SAD patients. This theory also accounts for the success of selective serotonin-reuptake inhibitors, such as Prozac and Zoloft, when administered to patients suffering from depression. (4).

Luckily, as with clinical depression, SAD is treatable. Studies have proven light therapy to be the most successful method of controlling the illness. Exposing patients to non-ultraviolet light above 1500 lux, or 150 footcandles, has shown to affect respiration, blood pressure, body temperature, and the production of melatonin. (7). The type of light used for therapy is inconsequential (no appreciable differences in effectiveness were discovered among fluorescent, incandescent, and high intensity discharge units) though UV light is discouraged for its carcinogenic properties. It is rather the strength of light and duration of exposure that is crucial for successful therapy. A typical session using modern light boxes, which emit about 10,000 lux, lasts approximately 30 minutes. (9). Interestingly, best results have been obtained when the light sessions are performed before 10 am. Treatments administered later in the day were not effective, and even made symptoms worse in some cases. After approximately two weeks of this frequency and duration, sessions can be reduced to 15 minutes per day, and eventually to every other day. (7). (For reference, a typical home is lit at twilight by 250 lux, and mid-summer sun can produce almost 120,000 lux.) (9). While light therapy does appear to work for the majority of SAD patients, antidepressants are another alternative for more severe cases.

The only known way to prevent Seasonal Affective Disorder is to live in a warm, southerly climate. But that doesn't mean that those of us who have chosen the north as our home must suffer endlessly at the hands of winter. Following some of the these suggestions can help alleviate many of the unpleasant symptoms associated with SAD: 1. Get more natural sunlight by doing outdoor chores and keeping windows and blinds open in the home and office. 2. Go outside and walk briskly (even in cold weather) once during the course of the day-particularly effective at midday. 3. Sit near a window, preferably in the sun, whenever possible. 4. Join a support group with other similarly-afflicted people. 5. Try phototherapy. 6. Go south for vacation! (9).

WWW Sources

1) UBC/VHHSC Mood Disorders Clinic

2) Student information site

3) Student information site

4) Light therapy site

5) AOL site , access might be limited

6) Depression and Related Affective Disorders Association

7) Global Industry Lighting center

8) Life Extension Foundation

9) site devoted to various types of depression

| Course Home Page | Back to Brain and Behavior | Back to Serendip |