S.A.D. and Circadian Rhythms

Allen Blaivas, M.D. Health Pro
  • If we had no winter, the spring would not be so pleasant: if we did not sometimes taste of adversity, prosperity would not be so welcome.


    - Anne Bradstreet, British poet


    It’s that time of the year again.  Especially for those of us not fortunate enough to live in warmer climes- the winter is coming.  As we all know, along with the season comes shorter days and longer nights.  Some of us may never even get to see the sun on the majority of our workdays, getting to work before it gets light and often leaving the office well after dark.  This can lead to a form of depression, known as seasonal affective disorder (SAD); perhaps more commonly called the “winter blues”.

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    SAD is defined as a major depressive disorder that recurs and improves with seasonal changes.  Most commonly these symptoms occur when going from fall into winter, but surprisingly this syndrome has also been shown to occur with a spring onset.  It has been estimated to occur in nearly 10% of the population over a lifetime, with some studies showing it to be more common with further distance way from the equator.  In other words, it is more common in places with shorter days and longer nights.


    While most studies showed that SAD occurred more commonly in women, at least one study showed that men actually had more severe episodes of depression when it did occur.  It seems more likely to occur at younger ages, with the average age being 23 years old, and decreasing in frequency as people get older.


    You might be wondering, why is this in a sleep blog?  Isn’t SAD a subtype of depression which is a psychiatric disorder?  The answer is that while SAD is a mental health disease, some of the suspected causes are related to our internal body clock, or circadian rhythm.  We have discussed the circadian rhythm on many occasions already, and have pointed how important light, particularly sunlight is to setting our biological clocks.  When the amount of sunlight we are exposed to decreases with the decreasing length of daylight our internal clocks lag and have been implicated as a possible basis of SAD.  Another possible cause of SAD related to our circadian rhythm is that melatonin secretion in the brain is increased.  As we have noted in previous blogs, melatonin is a hormone in the brain that increases over the course of the day and makes us sleepy.  Of course, melatonin secretion is also controlled by our exposure to sunlight.


    Another suggested cause of SAD is the brain chemical called serotonin.  Serotonin is one of many chemicals in the brain that have been tied to depression.  In fact, many of the more common antidepressants, such as Prozac and Zoloft work by increasing the level of serotonin in the brain.  Serotonin levels vary from season to season, with the lowest levels found in the months of December and January.


    In the next blog, we will review some of the controversy regarding SAD as a separate syndrome and explore some of the novel treatments for the winter blues.

Published On: December 02, 2008