Many see seasonal affective disorder (SAD) as synonymous with winter depression. However, depression is only half of the problem; spring and summer mania tend to be ignored. Beginning with winter depression, core symptoms resemble hibernation. People sleep more, eat more, and are less interested in usual activities. They are not sad in mood, typically, and may be unaware that their slowed down, uninterested behavior reflects a kind of depression.
Moreover, light itself is not the only cause of depression. Light interacts with a person's own sensitivity to depression. Some people, especially those with bipolar disorder or recurrent unipolar depression, are sensitive to changes in light, and will develop winter depression even in areas with reasonable light levels, such as Georgia or Italy. Others are insensitive to light, and will not develop SAD even in areas with low light levels, such as New England or Scandinavia.
This leads to another misconception about SAD. It is a diagnosis of exclusion, and should not be diagnosed in persons with bipolar disorder or recurrent unipolar depression. SAD means someone has only depression in the winter, and almost never has depression any other time of year.
Light entrains our circadian rhythms; it is what keeps us on regular sleep-wake cycles. When sleep is impaired and reduced, an antidepressant effect occurs, and, in sensitive persons, mania materializes. This is what takes place in the spring and summer when light greatly increases. Longer duration of sleep leads to depression in sensitive persons. Circadian cycles appear to be biologically abnormal in people with bipolar disorder and recurrent depression, hence their sensitivity to light. One of the effects of lithium, for instance, is to lengthen circadian cycles, which appear to be abnormally shortened in animal models of mania.
I've developed my own recommendations for both winter depression and summer mania, which one could call "light precautions." They are as follows, briefly.
In winter. Increase your exposure to light as much as possible. Go out for a walk at noon for up to an hour without any sunglasses on; sleep with all the blinds up.
In summer. Reduce your exposure to light as much as possible: Always wear sunglasses; get room-darkening shades; and sleep in as much darkness as possible. (It is key to adjust one's exposure to natural morning sunlight. It is amazing how many people who oversleep never think of pulling up their window shades, and how many people who don't sleep enough don't think about getting room-darkening window shades.)
Light Box Treatment
Light box treatment essentially replaces the sunlight that is missing in wintertime. Most light boxes provide about 10,000 lux of light, and are meant to be used in the mornings, which is when the sun would normally have risen earlier than it does in the depths of winter. Patients should read or eat breakfast while exposed to indirect light from the box at about arm's length for about 30 minutes daily. Just as one does not directly look at the sun, patients should not directly look at light boxes; this causes ocular damage.
The Truth About Seasonal Affective Disorder
