To Your Health

A. Seasonal Affective Disorder is a type of winter depression that affects an estimated half a million people in the lower United States during December, January, and February. This is about 6% of us, but in Alaska and Canada SAD may affect as much as 10% of the population. For some SAD is a seriously disabling illness, preventing them from functioning normally. For others it causes mild discomfort but not severe suffering. In addition to the "blues," most sufferers show signs of a weakened immune system and are more vulnerable to infections.

SAD was first scientifically described in 1984 but has roots in the observations of John Ott, who made several nature documentary films for Walt Disney in the Fifties. Ott was intrigued by the connection between varying light waves and plant growth patterns, and later carried his theories over into the animal world. Animals react to the changing light/dark patterns of the seasons with changes in mood and behavior. Apparently human beings are no different. Most people find they eat and sleep slightly more in winter and dislike the dark mornings and short days. If the symptoms are severe enough to disrupt their lives and to cause considerable distress it is called SAD.

SAD is caused by a biochemical imbalance in the hormones from the hypothalamus in response to the shortening of daylight hours in winter. Although researchers are not certain what gives rise to SAD, they suspect that it has something to do with the hormone melatonin. Melatonin plays a central role in regulating the "internal body clock," which dictates when humans feel like going to bed at night and getting up in the morning.

The body produces more melatonin at night than during the day. There is also more melatonin in the body during winter, when the days are shorter. Some researchers believe that in people with SAD, excessive melatonin release during winter may account for their feelings of drowsiness or depression. One consistent observation is that melatonin causes body temperature to drop, which may result in loss of energy and perhaps eventual depression.

Bright, fluorescent (not ordinary) light has been shown to reverse the symptoms of SAD. Ordinary light bulbs are not strong enough. Average house lighting produces only about 10-20% of the minimum light necessary to treat SAD, and the light intensity on a bright summer day can be 100-200 times that of house light. Persons with SAD generally begin with 30 to 45 minutes of light treatment first thing in the morning because light treatment in the evening may cause insomnia. Scientists believe that light therapy works by altering the levels of melatonin, but the past decade of research has shown SAD to be more complicated than first thought, and the mechanism of light therapy is still mysterious.

Daily exercise has been shown to be helpful, particularly when done outdoors. For those who tend to crave sweets during the winter, a reduction in sweets may help one's mood. Conversely, as the mood improves, craving for sweets may decrease.

Most people with SAD respond to light therapy, but it may be that we simply become more vulnerable to feelings of aloneness and other sad thoughts because in winter the shorter day-length sets the stage for depression.