Seasonal Affective Disorder (SAD)
Why is it that on sunny days our mood is more upbeat than on dull, gray days? Why do we experience the irresistible urge to get away to a sunny climate in the dead of winter? The answer is that light energizes us and improves health. In fact, for health problems like depression and sleep problems, light can even be more effective than drugs.
When was the last time you saw the Milky Way or a star-lit night sky, sights our ancestors witnessed on a regular basis? The "light pollution" of urban environments means that many people also don't receive exposure to true darkness anymore. Consider how for almost our entire evolution as hunter-gatherers, we were exposed to the natural cycles of sunlight during the day and darkness at night. But with the advent of modern technology, we have significantly altered our exposure to light and darkness. Electricity has allowed us to stay awake and active well into the night while we have moved our daily activities from outdoors to indoors.
For these reasons, we get little exposure to natural sunlight or true darkness. We spend our days working or living indoors away from natural light while at night, we are exposed to indoor light and the constant illumination of city-lit skies. How much time do you spend each day in bright sunlight? If you are like most people, you probably spend very little time in sunlight. Studies have shown that no matter where people live, they usually obtain only one hour of sunlight on average during the day.
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The main reason we have little exposure to sunlight is that most of us work indoors. A brightly lit room has about 500 luxes of light (a lux is the equivalent of the light from one candle) compared to 10,000 luxes at sunrise and 100,000 at noon on a summer day. To the brain, spending the day indoors is equivalent to spending the day in darkness. The problem is compounded in the late fall and winter months when days grow shorter and many of us curtail outdoor activities. Our distant ancestors evolved on the savannas of Africa, but many of us now live in northern latitudes where ambient sunlight is significantly diminished during the winter.
That lack of exposure to bright light can adversely affect our sleep, daytime mood, energy and alertness levels. Earlier scientific studies on the effects of light on mood involved depression. In the early 1980s, scientists at the National Institute of Mental Health found that a patient who experienced depression and sleep problems annually during the fall and winter months (what is called 'seasonal depression') had their conditions improve after daily treatment of exposure to bright light. That single case study has since led to defining SAD (seasonal affective disorder), a disorder which is characterized by depression and sleep disturbance in the winter months, and extensive testing of the efficacy of bright light therapy. There is now scientific consensus that bright light therapy is effective for SAD, a disorder which may overlap with chronic and intermittent depression and sleep problems. People living in northern climates who spend six months a year in winter-type lighting conditions are more prone to SAD.
Besides affecting our mood, light also affects our sleep, which is important for restoring energy. Sleep and body temperatures are directly influenced by the effects of daily cycles of light and darkness on melatonin, a naturally occurring hormone found in the brain. When sunlight enters the eyes, melatonin levels decrease and raise the body’s temperature which causes wakefulness. Darkness causes melatonin levels to increase and the body’s temperature to fall, thereby inducing a sleep state.
By reducing our exposure to bright natural light and true darkness, melatonin secretion and the body temperature rhythms are altered which can exacerbate sleep difficulties. This explains why up to 90% of blind people experience sleep problems.
You can minimize SAD and sleep problems by increasing your exposure to sunlight. Aside from the obvious ways of increasing your exposure to natural bright light, you may want to consider the use of artificial bright light boxes. These devices contain special bulbs that emit 5000 -10,000 luxes of light, which is equivalent to a sunrise or sunset. They are used for about 30 minutes while reading or watching television to increase early or late day exposure to bright light. Several studies have demonstrated that using bright light boxes in the evening can delay body temperature rhythms and effectively minimize early morning insomnia. These studies also indicate that the boxes are effective in treating SAD. Light boxes can be rented from medical supply companies or purchased from an increasing number of manufacturers. Some insurance companies even reimburse the cost of light boxes if they are prescribed by a physician for SAD or insomnia.
