The Truth About Seasonal Affective Disorder

Nassir Ghaemi, MD, MPH


February 03, 2011

In This Article

Diagnosing SAD

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. The mood episodes that characterize those conditions can happen any time of year; they are just more likely in winter (for depression) and summer (for mania). SAD means someone has only depression in the winter, and almost never has depression any other time of year. This is actually quite infrequent, probably not more than 1%-2% of the US population.

Most people who think that they have SAD don't. If they have severe depression, their winter depressive episodes are usually part of a larger illness, whether bipolar or unipolar. Commonly, however, people think that they have SAD because indeed they have winter depressive-like symptoms, but not full clinical depressive episodes. This experience, sometimes called "winter blues," is common, and occurs in the general population at a frequency that varies depending on latitude: approximately 1% in Florida, 5% in the mid-Atlantic, and 10% in New England. Again, we can understand this prevalence as reflecting an interaction of light with the biological sensitivity of individuals to light.

Light and Mood

What does light do to cause changes in mood? 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. A specific gene, called the CLOCK (Circadian Locomotor Output Cycles Kaput) gene, appears to be related to abnormal circadian rhythms. Changes in light availability are an external way in which our circadian rhythms are lengthened or shortened. In most of us, these changes do not affect our moods; in others, they do.

Warding Off Seasonal Depression

Besides light box treatment (which we'll discuss) for seasonal depression, 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 amount of time with light box treatment can be increased or decreased as needed for antidepressant effect, which, unlike drugs, occurs quickly: usually within 1-2 weeks. If the patient improves, the light box can be reduced in frequency or duration to the minimum amount that seems to be needed. Usually, the decline in light starts in October-November, and that is when light box treatment can begin. Light then increases in March-April, and by then light box treatment should be stopped.