• Quote of the Day
    "Worrying is like a rocking chair: It gives you something to do, but it doesn't get you anywhere."
    Van Wilder, posted by Daniel

David Baxter

Mar 26, 2004
The Truth About Seasonal Affective Disorder
by Nassir Ghaemi, MD, MPH

The Saddest Time of Year
December 21 was the winter solstice: the shortest, hence darkest, day of the year. January 17 (some claim) is the "saddest day of the year," factoring in bad weather, postholiday withdrawal, and the usual effect of return-to-work Mondays on our moods. I believe that this belief is false. Winter is not the saddest time of the year; in fact, springtime is much worse.

Seasonal Affective Disorder vs Depression
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.

A number of misconceptions are harbored about winter depression. The most frequent, perhaps, is that it has to do with coldness of temperature. Winter depression is not about shivering and freezing. These do not cause depression; decreased light does. It doesn't matter whether it's 70?F or 20?F outside; if there are 10 hours of light in a day rather than 14, then seasonal depression will follow. When I worked in Atlanta, Georgia, many people who used to live in Florida came to me with SAD. Georgia had notably less light than Florida, even though temperatures were only slightly colder.

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.

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.

Can Light Be Harmful?
Now to springtime. "April is the cruelest month," T.S. Eliot famously said. This poetic insight makes sense, given the harmful impact of increased light in springtime. Again, most people think of SAD only in terms of winter depression, but springtime mania should not be ignored, especially because mania frequently reflects mixed states, when depression and mania occur together, and mixed states are linked with the highest risk for suicide. Indeed, a century ago Kraepelin showed a clear suicide spike in April, far higher than other months. Winter suicide rates are quite low; this has been replicated over and over.

The harmful effect of increased light may have something to do with another underappreciated fact. As Howard Kushner explained in his classic book, American Suicide, the highest suicide rates in the United States have always been in the sunny West, specifically California, and particularly the sunniest part of California: San Diego County. It's been this way for 100 years, despite all kinds of cultural and social changes. Obviously suicide is an olio of many ingredients, but could a biological catalyst be the dark side of SAD: too much light?

Whatever the case, we know that too little light can cause depression in people who are sensitive to it, especially those who already have mood diseases. However, let's not forget that too much light is, in many ways, just as bad.

January may be an unhappy month, but April is the cruelest.

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