Does Light Therapy Really Help with SAD?

Seasonal Affective Disorder
Seasonal Affective Disorder

Seasonal affective disorder (SAD) can be defined as a "recurring depression with seasonal onset and remission." 1 The Diagnostic and Statistical Manual (DSM-IV-TR) describes it as a "specifier" or a subtype that can occur within any major depressive disorder, bipolar I disorder, and bipolar II disorder.2 There are no planned major changes to the diagnosis of SAD in the upcoming DSM-5.3

Two seasonal patterns of SAD have been described: fall-onset and summer-onset SAD. The fall-onset type, also known as "winter depression," or "winter blues," is the most recognized, with symptoms beginning in late fall to early winter and remitting during summer months.1


In any given year, about 5% of Americans experience symptoms of SAD, lasting approximately 40% of the year.3 There is a 4:1 ratio of SAD in women, compared to men.3 Although remission usually occurs spontaneously with the change of the seasons, SAD is nevertheless considered a serious mental health problem, due to its recurrence, duration, impact on quality of life,3 and economic consequences, both individual and societal.4,5

Etiology and Pathophysiology

There are several putative biological mechanisms underlying SAD.3 Most commonly accepted is the phase shift hypothesis (ie, a phase delay or advance in the circadian rhythms associated with the sleep/wake cycle during the winter).6 Other possible mechanisms include retinal sensitivity to light, neurotransmitter dysfunction, genetic variations affecting circadian rhythms, and serotonin levels.3 Since SAD is a complex disorder, it likely is caused by a combination of these factors.3

Presenting Symptoms and Diagnostic Workup

DSM-IV-TR criteria for seasonal pattern specifier include:

  • Regular temporal relationship between onset of major depressive episodes at a particular time of year, unrelated to psychosocial stressors
  • Full remissions also occurring at characteristic time of year
  • Two major depressive episodes in the last two years and no nonseasonal episodes in the same period
  • Seasonal major depressive episodes that substantially outnumber nonseasonal episodes over an individual's lifetime2

Assessment tools may be useful in screening patients for SAD. The Seasonal Pattern Assessment Questionnaire (SPAQ) has been the most widely studied screening tool,7 but the Seasonal Health Questionnaire (SHQ) may have higher specificity and sensitivity than the SPAQ.7,8

The differential diagnosis is extremely important, as there may be considerable overlap between SAD and other conditions, including major depression, generalized anxiety disorder (GAD), bipolar disorder, panic disorder, bulimia nervosa, late luteal phase dysphoric disorder, chronic fatigue syndrome, and attention-deficit/hyperactivity disorder.7 A pattern of seasonal alcohol use may also be present.7


The two most widely accepted treatments for SAD are light therapy and pharmacotherapy. Because these interventions are similar in efficacy, other clinical factors, including patient preference, should guide selection of first-line treatment. 9

Light therapy has been demonstrated effective in numerous systematic reviews and meta-analyses and is a well-established first-line treatment.3 The Canadian Consensus Guidelines for the Treatment of Seasonal Affective Disorder offers several recommendations for effective use of light therapy:10

  • Use a fluorescent light box (10,000 lux) for 30 minutes per day.
  • Patients should sit about 12 to 18 inches from the light source.
  • Patients should avoid looking directly into the light.
  • Light boxes should use white fluorescent light with the ultraviolet wavelengths filtered out. Incandescent halogen lights should be avoided.
  • The optimal time of day for light therapy is early morning upon awakening, but exposure at other times of day may be effective for some patients.
  • Typical response time is one week, but some patients require two to four weeks to show a response.
  • There are no absolute contraindications to light therapy, and there is no evidence that light therapy is associated with ocular or retinal damage.

Although light therapy is generally well tolerated, there can be transient adverse effects, such as headache, eye strain, nausea, agitation, and blurred vision.3 To ensure adequate response to light therapy, patients should use units that are specifically designed to treat SAD.7

Pharmacotherapy  is recommended by several guidelines, including the CANMAT Guidelines,10 which recommend sertraline and fluoxetine as effective first-line pharmacologic treatments for SAD. Antidepressants should be used in doses similar to those used in the treatment of nonseasonal depression. An adequate trial of antidepressants involves at least six weeks of treatment.10 Bupropion has been found to be effective prophylaxis for SAD, if administered in early autumn.11

Additional Treatments

CBT has been widely studied and empirically validated for use in nonseasonal depression.3 It has also shown modest efficacy in both treatment and prophylaxis of SAD.3 Additional interventions include exercise, relaxation and stress management techniques, spending more time outdoors, and visiting sunnier, warmer climates.3


1. Saeed SA, Bruce TJ. Seasonal affective disorder. Up to Date. Available at: Accessed: December 19, 2012.

2. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR), Fourth edition. Washington. DC: American Psychiatric Association, Washington, DC 1994.

3. Kurlansik SL, Ibay AD. Seasonal affective disorder. Am Fam Physician. 2012;86(11):1037-1041.

4.Tefft N. Mental health and employment: the SAD story. Econ Hum Biol. 2012;10(3):242-255.

5. Cheung A, Dewa C, Michalak EE, et al. Direct health care costs of treating seasonal affective disorder: a comparison of light therapy and fluoxetine.

6. Lewy AJ, Rough JN, Songer JB, et al. The phase shift hypothesis for the circadian component of winter depression. Dialogues Clin Neurosci. 9(3): 291–300.

7. Thompson C, Thompson S, Smith R. The Seasonal Health Questionnaire is more effective at detecting seasonal affective disorder than the Seasonal Pattern Adjustment Questionnaire. J Affect Disord. 2004;78:219-236.

8. Lurie AJ, Gawinski B, Pierce D, Rousseau SJ. Seasonal affective disorder. Am Fam Physician. 2006;74(9):1521-1524.

9. Lam RW, Levitt AJ, Levitan RD, et al. The Can-SAD study: a randomized controlled trial of the effectiveness of light therapy and fluoxetine in patients with winter seasonal affective disorder. Am J Psychiatry. 2006;163(5):805-12.

10. Lam RW, Levitt AJ. Canadian Consensus Guidelines for the treatment of seasonal affective disorder. 1999 Clinical & Academic Publishing. Available at: Accessed: December 19, 2012.

11. Modell JG, Rosenthal NE, Harriett AE, et al. Seasonal affective disorder and its prevention by anticipatory treatment with bupropion XL. Biol Psychiatry. 2005;58(8): 658-667.

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