By Nikita Katz, MD, PhD
Seasonal affective disorder (SAD), also known as winter depression and winter blues, is a type of mood disorder that is typically caused by low light levels. SAD generally begins in the fall and worsens during the winter months. The rarer, reverse seasonal affective disorder (summer blues, summer depression) begins in the spring and worsens in the in the summer.
SAD is generally found more frequently in people who live in latitudes far north or south of the equator (for example, one percent in Florida; four percent in Washington, D.C.; 10 percent in Alaska). Some patients experience a serious mood change when the seasons change. They may sleep too much, have little energy, and crave sweets and starchy foods. They may also feel depressed. Although symptoms may be severe, they generally resolve over several months.
SAD can be a serious disorder that may require hospitalization. There is a potential risk of suicide among some individuals experiencing SAD. The symptoms of SAD mimic those of clinical depression or dysthymia. The prevalence of SAD in the adult American population has been estimated at between 1.5 percent in Florida and about nine percent in the northern US. Overall, 6.1 percent of the US population is affected by SAD. Subsyndromal seasonal affective disorder is a milder form of SAD estimated to affect 14.3 percent of the American population.
Seasonal affective disorder is more common in women than men and in people between the ages of 15 and 55 years. The risk of developing SAD for the first time decreases with age. People who have a close relative with SAD are also at greater risk.
There is strong evidence that SAD is caused by a lack of available sunlight. Decreased exposure to sunlight may have an effect on the body’s biological clock, which regulates mood, sleep, and hormone production. Exposure to light may reset the biological clock. Melatonin and serotonin synthesis may be altered in individuals with SAD. Exposure to light appears to correct both neurotransmitter deficits and changes in the biological clock.
Symptoms of SAD include difficulty waking up in the morning, a tendency to oversleep, to overeat, and to crave carbohydrate-rich foods, often leading to weight gain. Other symptoms include a lack of energy, difficulty concentrating on completing tasks, and withdrawal from friends, family, and social activities. Individuals with SAD are characterized by depression, pessimism, and a lack of pleasure in usual activities. Symptoms of SAD can include heightened anxiety as well as depression. For most people with SAD, symptoms start in September or October and end in April or May and tend to occur at the same time every year.
There are several treatment options for classic SAD. Bright-light treatment uses a specially designed lamp (or light box) — with an intense “full spectrum” or blue light at doses of 2,500 to 10,000 lux. The patient sits at a prescribed distance, usually 30 to 60 cm, in front of the box with eyes open but not staring at the light source for 30 to 60 minutes. Many individuals use the light box in the morning, and there is evidence that morning light is superior to evening light although people may respond to evening light as well. One study found that up to 69 percent of patients find the treatment inconvenient, and as many as 19 percent stop use because of this.
There is evidence that dawn simulation is effective as well. In some studies, this has been found to be 83 percent more effective than other bright-light therapies. Most studies have found light therapies to work well — for several weeks — as seasonal treatment until greater amounts of natural light are available.