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Seasonal Affective Disorder Back to Course Index








It is important to recognize that SAD is not a stand-alone mental disorder; however, it is a subset or “specifier” to other mood disorders and often helps explain their occurrences and characteristics.  Consequently, it is important to understand the general criteria for depression (and other mood disorders) in order to understand the role SAD plays in the overall depression picture.  This CEU will initially address some of the characteristics of depression and then explain how SAD is diagnosed and treated.  We will start with a basic question of “what causes depression”.   When this question is posed to me I respond with a comment such as “several things”.  For example, there may be biological factors (including biochemical and/or genetic), psychological factors (such as coping skills and temperament) and social factors (family and support network).  Some health care professionals suggest an entirely biological cause of depression, describing it as a serious disease caused by a chemical imbalance in the brain.  This is consistent with the cultural shift that attempts to explain all of our problems by biology (I have a chemical addiction).  The result of that approach is that we don’t need to take personal responsibility for anything and don’t need to make personal changes.  The major problem with this view of depression (that it is caused by a chemical imbalance in the brain) is the fact that depression can be both triggered by and resolved by life events.  The misconception is that the brain somehow develops a chemical imbalance and the result is depression, occurring in a single directional process.


Depression is a serious medical condition.  The initial indication may be symptoms of anxiety (exemplified by excessive worry) or symptoms such as sadness or lack of energy.  These symptoms may last for days or months before the onset of Major Depression.  After the progression to Major Depression, an individual may have trouble concentrating or remembering, experience a loss of pleasure in things that they once enjoyed, feel hopeless, experience a loss of energy or loose interest in sexual activity.  The course of depression varies from individual to individual.  One person may have mild or severe symptoms of depression for a long time, or they might occur for only a short time.  A few individuals feel depressed for most of their lives and require ongoing treatment.  The good news is that most individuals who have depression can be treated successfully with medication, professional counseling or both.




Merriam Webster’s Medical desk dictionary, 1993, defines Seasonal Affective Disorder (SAD) as “depression that tends to recur as the days grow shorter during the fall and winter”.  This definition has been expanded by other sources to specify a type of depression that follows the seasons with the most common type being winter depression.  It usually starts in the fall and goes away the following spring. 


Psychologist’s first noted SAD in the mid-1800’s; however, it was not officially named until the mid-1980’s.  The early researchers indicated that SAD might be an effect of seasonal light variations due to the environmental changes related to the seasonal changes.  Also, they noted there might be a shift in our “biological clocks” due partly to these changes in sunlight patterns.  This can cause our biological clocks to be out of sequence with our daily schedules.  The most difficult months for SAD sufferers are January and February.  Some researchers have concluded that younger persons and women are at higher risk for SAD.  The National Mental Health Association estimates that SAD severely affects five percent of the population while slightly affecting another 20 percent.


The symptoms associated with SAD include depression, loss of energy, weight gain, overeating, excessive sleep, and lack of energy during the winter months.  The symptoms may be caused by an overproduction of melatonin.  The National Mental Health Association found that melatonin (sleep controlling hormone) is overproduced in the brain when exposed to darkness.  This is why places of lower latitude are believed to be therapeutic to SAD sufferers.  For example, a student in a southern university would be exposed to more light during the winter months that would decrease his or her melatonin levels.




Depressive disorders are classified according to their severity and duration.  Depression may be mild, moderate or severe.  It may start suddenly (acute) or be long lasting (chronic).  For severe depression, an individual may need to be admitted to a hospital for short-term treatment, especially if the individual is having thoughts of suicide (depression puts an individual at a higher risk for attempting suicide; consequently, an individual should seek immediate treatment if he or she is having self-destructive thoughts).  Depression often recurs; consequently, if an individual has had an episode of depression they are more likely (then the general population) to again become depressed.  Also, the risk of having another episode increases with each additional episode.


Specifically focusing on SAD, the Diagnostic and Statistical Manuel of Mental Disorders (DSM-IV) does not describe it as a unique, stand-alone psychological disorder; however, a specifier that denotes the seasonal relationship is used in conjunction with other mood disorders such as major depression.  Based on this approach this CEU will first present the DSM-IV diagnostic criteria for Major Depression and then present the criteria for the seasonal pattern specifier.   


The DSM-IV criteria for diagnosis of a Major Depressive Episode is:


A.     Five (or more) of the following symptoms have been present during the same 2-week period and represent a change from previous functioning; at least one of the symptoms is either (1) depressed mood or (2) loss of interest or

pleasure.  Note:  Do not include symptoms that are clearly due to a general  medical condition or mood-incongruent delusions or hallucinations.


1)      Depressed mood most of the day, nearly every day, as indicated by either subjective reports (e.g., feels sad or empty) or observations made by others (e.g., appears tearful).  Note: In children and adolescents, can be irritable mood.

2)      Markedly diminished interest or pleasure in all, or almost all activities most of the day, nearly every day (as indicated by either subjective account or observation made by others).

3)      Significant weight loss when not dieting or weight gain (e.g., a change of more than 5% of weight in a month), or decrease or increase in appetite nearly every day.  Note:  In children, consider failure to make expected weight gains.

4)      Insomnia or hypersomnia nearly every day.

5)      Psychomotor agitation or retardation nearly every day (observable by others, not merely subjective feelings of restlessness or being slowed down).

6)      Fatigue or loss of energy nearly every day.

7)      Feelings of worthlessness or excessive or inappropriate guilt (which may be delusional) nearly every day (not merely self-reproach or guilt about being sick).

8)       Diminished ability to think or concentrate, or indecisiveness, nearly every day (either by subjective account or as observed by others).

9)      Recurrent thoughts of death (not just fear of dying), recurrent suicidal ideation without a specific plan, or a suicide attempt or a specific plan for committing suicide.


B.     The symptoms do not meet criteria for a Mixed Episode.

C.     The symptoms cause clinically significant distress or impairment in social, occupational, or other important areas of functioning.

D.     The symptom’s are not due to the direct physiological effects of a substance (e.g., a drug of abuse, a medication) or a general medical condition (e.g., hypothyroidism).

E.      The symptoms are not better accounted for by Bereavement, i.e., after the loss of a loved one, the symptoms persist for longer than 2 months or are characterized by marked functional impairment, or psychomotor retardation.


The specifier With Seasonal Pattern can be applied to the pattern of Major Depressive Episodes in Bipolar I Disorders, Bipolar II Disorders, or Major Depressive Disorder, Recurrent.  The essential feature is the onset and remission of Major Depressive Episodes at characteristic times of the year.  In most cases, the episodes begin in fall or winter and remit in spring.  Less commonly, there may be recurrent summer depressive episodes.  This pattern and remission of episodes must have occurred during the last 2 years, without any non-seasonal episodes occurring during this period.  In addition, the seasonal depressive episodes must substantially outnumber any non-seasonal depressive episodes over the individual’s lifetime.  This specifier does not apply to those situations in which the pattern is better explained by seasonally linked psychosocial stressors (e.g., seasonal unemployment or school schedule).  Prominent energy, hypersomnia, overeating, weight gain, and craving for carbohydrates often characterize Major Depressive Episodes that occur in a seasonal pattern.  It is unclear whether a seasonal pattern is more likely in Major Depressive Disorder, Recurrent, or in Bipolar Disorders.  However, within the Bipolar disorders group, a seasonal pattern appears to be more likely in Bipolar II Disorder than in Bipolar I Disorder.    In some individuals, the onset of Manic or Hypomanic Episodes may also be linked to a particular season.  Bright visible-spectrum light used in treatment may be associated with switches into Manic or Hypomanic Episodes.


The prevalence of winter-type seasonal pattern appears to vary with latitude, age, and sex.  Prevalence increases with higher latitudes.  Age is also strong predictor of seasonality, with younger persons at higher risk for winter depressive episodes.  Women comprise 60% to 90% of persons with seasonal patterns, but it is unclear whether female gender is a specific risk factor over and above the risk associated with recurrent Major Depressive Disorder.  Although this specifier applies to seasonal occurrence of full Major Depressive Episodes, some research suggests that a seasonal pattern may also describe the presentation in some individuals with recurrent winter depressive episode that do not meet criteria for Major depressive Episode.


The DSM-IV criteria for a Seasonal Pattern Specifier is (specify if): 


A.     There has been a regular temporal relationship between the onsets of Major Depressive Episodes in Bipolar I or Bipolar II Disorder or Major Depressive Disorder, Recurrent, and a particular time of the year (e.g., regular appearance of the Major Depressive Episode in the fall or winter).


Note:  Do not include cases in which there is an obvious effect of seasonal-related psychosocial stressors (e.g., regularly being unemployed every winter).


B.     Full remissions (or a change from depression to mania or hypomania) also occur at a characteristic time of the year (e.g., depression disappears in the spring).


C.     In the past 2 years, two Major Depressive Episodes have occurred that demonstrated the temporal seasonal relationships defined in Criteria A and B, and no non-seasonal Major Depressive Episodes have occurred during that same period.


D.     Seasonal Major Depressive Episodes (as described above) substantially outnumber the non-seasonal Major depressive Episodes that may have occurred over the individual’s lifetime.


A number of “specifiers” for Mood Disorders are provided to increase diagnostic specificity and create more homogeneous subgroups, assist in treatment selection, and improve the prediction of prognosis.  Specifiers that describe the course of recurrent episodes include Longitudinal Course specifiers (with or without Full Inter-episode Recovery), Seasonal Pattern, and Rapid Cycling. 




If an individual thinks they have depression they should contact a health professional who will give them a physical examination and inquire as to their general health.  The doctor may also recommend additional tests such as:


·          Comprehensive laboratory tests to “rule out” other possible causes (for depression like symptoms) such as under-active thyroid or anemia,

·          A mental health examination by a health professional,

·          Written or verbal questionnaires targeted to help with diagnosis.


The health professional will determine the severity of the depression and how it may be affecting normal activities.  The health professional may also ask questions to determine whether the individual is having any suicide ideations.


If an individual has ever experienced manic episodes (a period of abnormal happiness, irritability, or intense energy that lasts 4 days or longer) they should inform their health care professional.  Manic episodes or milder hypomanic episodes, along with depression, could mean they have a bipolar disorder. 


Anytime someone visits with their health professional, it is important to discuss any symptoms that may be caused by depression.  About half of all cases of depression are undiagnosed or under treated; consequently, healthcare professional are being encouraged to ask questions about depression and also to obtain sufficient data to identify applicable specifier (seasonal pattern specifier or others).




Phototherapy (bright light therapy) has been effective in suppressing the brain’s secretion of melatonin; however, no research has linked the reduced melatonin to an antidepressant effect.  Regardless of the lack of clinical verification, many people have responded favorably to this therapy.  The device most often used is a bank of white fluorescent lights on a metal reflector and shield with a plastic screen.  For mild episodes of seasonal induced depression, spending time outdoors during the day or arranging homes to receive more sunlight may be helpful.  Researchers are continuing to validate phototheapy as a viable treatment modality.  The latest studies are based on rigorous methodology with larger sample sizes and increased treatment periods.  Also, the wavelength of light was evaluated in two studies. In one study, cool-white fluorescent lights were found to be as effective as full-spectrum fluorescent lights.  This result supports other studies that indicate that various light sources (including incandescent lights) are effective for treating SAD. Devices such as visors have also been evaluated for light therapy.  The conclusion indicates there was no relationship between the intensity of light and various measures of response to treatment (very low intensity light was used). This contrasts to most light box studies that indicate light intensity is a controlling parameter. This difference may be explained in that the visor is closer to the eye, which increases the amount of light that reaches the retina.  There is also increasing evidence that even low illumination can affect biologic parameters (light as low as 100 lux may be therapeutically effective). 




Light therapy is generally considered a benign treatment with few side effects; however, mild side effects, including headache, eyestrain, and “feeling wired” were reported by about 20 percent of patients.  Most researchers indicate that there is a potential for damage to the retina due to long term exposure to bright light; however, the intensities of light used in light therapy regimens are not considered harmful to the human retina based on short term studies, but the retinal effects of long term bright light exposure are not known. Some researchers have recommended an ophthalmologic evaluation prior to starting light therapy.  At a minimum, ophthalmologic screening should be performed on patients with a history of retinal disease, patients on photosensitizing medications, and the elderly.


Also, antidepressant drugs are being studied in SAD.   One case study suggested that citaloprim was as effective as light therapy.   It has also been reported that Fluoxetine is as effective as light therapy for SAD.   A question remains is whether a combination of medications and light therapy is more effective than either alone.





Q1       What type of light therapy is best?


Answer:  The most frequently used types of light therapy are bright light and dawn simulation.  As the name indicates “bright light” delivers a large amount of light.  This light source can augment nature on overcast days that have less natural light or when one remains indoors.  The light boxes are the most frequently used type of artificial light and is most frequently used for light therapy.  Light visors are also a convenient way of getting light therapy and have an advantage in that the patient can be mobile while undergoing therapy.


The concept behind dawn simulation is that it mimics a natural sunrise by slowly increasing light as the patient wakes-up. This technique can be used in conjunction with bright lights or for milder episodes and is especially effective in cases where the patient has difficulty with early morning activates.


 Q2    Can my doctor help me get a light?


Answer:    Health insurers will often pay for a patient’s light box.  If light therapy is prescribes, please inform your doctor if your are taking any medications (especially anti-depressants) as the dosage may need to be adjusted.


Q3     Frequency of use


Answer:   Application of light therapy varies by individual but most use almost daily (especially during winter).  Some patients have noted a return of symptoms after they miss a day or two.  Some patients have also found that they need less light therapy when it is bright outside and they can be outside.  When the season changes (spring) and the days get brighter, the general tendency is to use less light therapy.


Q4     How long is therapy session?


Answer:  The higher intensity light boxes take about one-half hour to use each day. Typically, the light box provides about 10,000 lux (measure of the intensity of light) at approximately two feet. Mid-power light boxes deliver about one-half the light and take around 1 hour. After a few days, if your symptoms have improved, you could gradually cut down and see if you notice any difference.


Q5    When is the optimum time to apply light therapy?


Answer:   Morning applications are most frequent and work best for most individuals.  If multiple sessions are required it is generally best to do one in the morning and one in the evening.  Avoid using light therapy late in the evening though (i.e. within 3 hours of going to bed) as it may cause minor insomnia.  If you are lethargic in the mornings then you should try the light therapy first thing, even if you only have time for a short application. In this situation, a dawn simulator could also be beneficial.


Q6    How much does it cost to run?


Answer:   Light boxes are designed to be energy efficiency; consequently the cost to operate is minimal. Bulb life is approximately 500 hours. Light boxes are typically guaranteed for three years.


Q7    How safe is light therapy?


Answer:   Light boxes are considered benign treatment with a few mild side effects.  The light boxes produce less ultra-violet light than one is exposed to in normal daylight; consequently, there is minimal risk to skin or over exposure to UV while undergoing light therapy. A few cases of eyestrain have been reported.  This condition can usually be resolved by a temporary halt of therapy followed by a gradual build-up of exposure time that works be for you. There are no indications that light boxes or light visors cause any damage to the eye; however, an optical examination is recommended.


Q8     Are light boxes safe for children?


Answer:  Light boxes are safe for children; however, they are electrical devices so younger children should always be supervised.  No secondary or side-affects of light boxes have been identified.  There has been very little research involving babies and light therapy so, to be on the safe side infant exposure should be avoided.


Q9    What if I’m pregnant?


Answer:   All the evidence suggests that light therapy is safe for pregnant women and nursing mothers (though not while actually breast-feeding).  In fact, some researchers are now working on using light therapy to treat pregnant women for depression rather than anti-depressants medications.


Q10     Can I wear eyeglasses or contact lens when using a light box?


Answer:  Eye-glasses or contact lenses may be worn when using a light box or a light visor; however, it should be noted that sunglasses, photo-sensitive or tinted lenses can reduce the effectiveness of light therapy.


Q11    Is SAD and winter blues the same?


Answer:   SAD symptoms are typically referred to as winter blues.  Most symptoms occur during the winter months and include problems sleeping, difficulty in getting up, dreading the dark mornings and over-eating.




Diagnostic and Statistical Manual of Mental

Disorders, fourth Edition, 2000


Merriam Webster’s Medical; Desk dictionary, 1993


Various Internet websites