At 7:20 a.m. every year on February 2, thousands of people gather in western Pennsylvania as Punxsutawney Phil leaves his burrow at Gobbler’s Knob, observes the weather conditions, looks for his shadow, and makes his prediction regarding whether there will be an early spring or six more weeks of winter.
For those who live in northern climes where there is little sunlight in the winter, who develop daytime sleepiness, depressive symptoms, food cravings (especially for carbohydrates) and weight gain, spring can’t come soon enough. They suffer from Seasonal Affective Disorder (SAD), also called winter depression, and its incidence increases the closer one lives to the North and South Poles. Thus we see more SAD in Alaska (almost 10% of the population) than in Florida (less than 2% of the population), with the symptoms lessening as the days grow longer.
A Genetic Factor
The common wisdom is that SAD is light-related, and therefore, extending the day with artificial light has been described as a treatment. However, recent research suggests that light therapy is only part of the story.
While the reduced amount of daylight during the winter plays an important role in SAD, the syndrome cannot be traced to the amount of daylight exposure alone. Rather, recent research suggests that susceptibility to SAD may be related to variations in genes responsible for the production of a pigment called melanopsin. Specialized cells (called ganglion cells) in the retina contain the light-sensitive melanopsin pigment and are believed to play a role in resetting our circadian clock as well as setting our mood. That may explain why some northern populations, such as those of Icelandic descent in Iceland and Canada, may be protected from developing SAD. It has been hypothesized that in patients with SAD, retinal sensitivity to light is decreased and that, together with the reduction in winter light, these factors act synergistically to trigger winter depression.
Some researchers have used the phrase “circadian desynchrony” to describe the mismatch between a person’s circadian clock and the world around her. This desynchrony can have an effect on mood. Patients with SAD spend more time in bed awake, require more time to fall asleep, and more often experience poor sleep quality. The combination of these factors can impact several hormone systems, including those involved in appetite control and metabolism. Reduced sleep time changes the levels of hormones that control appetite (leptin and ghrelin) and may negatively impact how the cells in the body respond to the hormone insulin. As if adding insult to injury, the lack of a good night’s sleep can also make you grumpy and lead to weight gain.
New Therapies on the Horizon
Starting in October and throughout the winter season (for those of us in the Northern Hemisphere), a 30-minute exposure first thing every morning to bright light — whether natural sunlight or a “light box” — can be effective in treating or preventing SAD. Since the circadian system is especially sensitive to blue light, researchers are studying the effectiveness of a lower intensity and duration of exposure to blue enriched light. Light exposure is also now being used to treat non-seasonal depression. However, the jury is still out on whether these light treatments have negative effects on vision. What is really intriguing is that light aimed into the ear canal may have antidepressant effects!
Since SAD is a form of depression, its mood effects can be treated with antidepressants. Interestingly, there is little evidence that the hormone melatonin itself has a positive effect on depression or SAD. However, agomelatine, a new antidepressant compound available in some countries, may be effective. This medication stimulates melatonin receptors in the brain and antagonizes serotonin receptors.
While Seasonal Affective Disorder is not usually life-threatening, it can lead some patients to suicidal ideation. Patients with significant symptoms will benefit from treatment and must seek professional help. It has been reported from a research group in Vancouver, Canada, that light therapy may lessen suicidal thoughts in patients with SAD.
Seasonal Affective Disorder, like all mental illness, is real, and researchers continue to study how best to address its symptoms. Fortunately, its effects wane as the days grow longer. Here’s hoping that because Punxsutawney Phil didn't see his shadow on February 2, that we will have an early spring!
In “The iGuide to Sleep,” an Apple iBook that I wrote for the iPad, there is section about Seasonal Affective Disorder that includes a virtual lightbox. This virtual lightbox has not been clinically tested and is provided only to show what blue enriched light looks like on a tablet device. People suffering from SAD should not treat themselves, but should seek treatment from a clinician familiar with all aspects of treating SAD.
Michael and Jiuan Terman have written an excellent chapter on the specifics of light therapy (Chapter 149: Light Therapy), in Kryger M, Roth T, Dement WC ,Eds., Principles and Practice of Sleep Medicine (Elsevier, 2011).
Jurvelin H, Takala T, Nissilä J, et.al. Transcranial bright light treatment via the ear canals in seasonal affectivedisorder: a randomized, double-blind dose-response study. BMC Psychiatry. 2014 Oct 21;14(1):288.
Stephenson KM, Schroder CM, Bertschy G, Bourgin P. Complex interaction of circadian and non-circadian effects of light on mood: shedding new light on an old story. Sleep Med Rev. 2012 Oct;16(5):445-54.