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    Seasonal Depression

    As the days become longer more people begin to notice the impact that daylight has upon our bodies.  Though most
    people know that light is essential to regulation of our internal biological clock, only some know that light also plays
    a role in the regulation of mood, and even fewer understand the biological process that explains the relationship
    between darkness and depression.

    Years ago, Dr. Norman Rosenthal at the National Institute for Mental Health found that some patients became very
    sluggish, irritable, and depressed as days grew shorter.  They slept excessively, binged on carbohydrates, and
    withdrew from social activities.  In essence, their depressed behavior replicated a mild form of primitive biological
    hibernation.

    This type of mood change in response to the decreased exposure to daylight is known as Seasonal Affective Disorder
    (SAD).  The incidence of SAD in various regions of the world is directly related to each particular region’s distance
    from the equator.  That is, SAD is found with higher frequency in locations furthest from the tropics, where there
    are fewer hours of daylight.

    For those with SAD, the critical variable is not the season, nor the climate, nor other situational factors such as
    changes in employment status.  The depression is activated and deactivated by the amount of daylight.

    There is a biological explanation of the mechanism:  
    Light entering our eyes through the retina transmits impulses along the optic nerve to the hypothalamus.  This
    brain structure controls numerous activities including sexual urges, thirst and hunger, body temperature,
    aggression, and emotions such as pleasure and sadness.

    The hypothalamus transmits information about light to the pineal gland which regulates the production of
    melatonin which acts on the hypothalamus.  Melatonin induces sleep, decreases mental agility and appears to
    depress mood.  Absence of light results in increased melatonin secretion and SAD.

    SAD can be effectively treated via various behavioral changes.  Maintaining a regular sleep and wakefulness
    schedule even on weekends and getting regular exercise can combat some of the symptoms.   In addition, use of a
    specially designed light box which mimics sunlight can also be very helpful.

    Light therapy has been used to treat SAD since the 1980’s.  These specially designed light boxes contain high
    intensity full-spectrum light bulbs placed behind a diffusing screen which filters out the glare and almost 100% of
    the UV rays.

    The light emitted from a typical box at a comfortable distance is equivalent to a clear sunny spring morning.  
    Exposure times of as little as 15 to 30 minutes a day are sufficient to halt melatonin production.  Exposure in the
    morning is recommended for those who struggle to wake up during the winter months.  Exposure in the evening is
    preferable for those who feel sleepy in the early evening.

    If you think that you may have SAD it is important that you consult a professional in order to get an accurate
    diagnosis.  Light therapy will not help if your symptoms are not the result of SAD.  Before starting light therapy it is
    important to rule out other diagnoses which would require other treatments, and to take precautions and evaluate
    contraindications for the use of a light box.
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