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NCCIH Clinical Digest

for health professionals

Seasonal Affective Disorder and Complementary Health Approaches: What the Science Says

January 2019

Clinical Guidelines, Scientific Literature, Info for Patients: 
Seasonal Affective Disorder and Complementary Health Approaches

Seasonal Affective Disorder

Light Therapy

There is some evidence that light therapy may be useful as a preventive treatment for people with a history of season affect disorder. The idea behind light therapy is to replace the diminished sunshine of the fall and winter months using daily exposure to a light box. Most typically, light boxes filter out the ultraviolet rays and require 20-60 minutes of exposure to 10,000 lux of cool-white fluorescent light, an amount that is about 20 times greater than ordinary indoor lighting.

What Does the Research Show?

  • A 2015 Cochrane review of one study involving 46 people concluded that there is limited evidence on light therapy as preventive treatment for patients with a history of seasonal affect disorder. Evidence is limited based on methodological limitations and small sample sizes of studies. The review authors noted that the decision for or against initiating preventive treatment of seasonal affect disorder or using other preventive options should be strongly based on patient preferences.
  • A 2004 randomized controlled trial of 98 participants examined the effect of light therapy and exercise on depressive symptoms, and found that both treatments, even in combination, seem to be well tolerated and effective on symptoms.
  • A 2001 randomized controlled trial of 57 participants with SAD found that symptom scores decreased by more than 40 percent after exposure to 4 weeks of bright white or dim red light.


  • Ultraviolet lights should be avoided because of the increased risk of skin cancer.
  • People should avoid staring directly into the light to avoid possible retinal injury.
  • Side effects are typically mild, and include vision issues such as blurry vision, photophobia, or headache.
  • Light therapy may induce mania in patients with unrecognized or undertreated bipolar disorder.

Cognitive Behavioral Therapy (CBT-SAD)

There is some evidence that cognitive behavioral therapy – SAD can be effective in reducing the recurrence and remissions of SAD and has been shown to be sustained at least between a first and second winter season.

Cognitive behavioral therapy (CBT) is type of psychotherapy that is effective for SAD. Traditional cognitive behavioral therapy has been adapted for use with SAD (CBT-SAD). CBT-SAD relies on basic techniques of CBT such as identifying negative thoughts and replacing them with more positive thoughts along with a technique called behavioral activation. Behavioral activation seeks to help the person identify activities that are engaging and pleasurable, whether indoors or outdoors, to improve coping with winter.

What Does the Research Show?

  • A 2016 randomized head-to-head trial of 177 participants found that CBT-SAD was superior to light therapy two winters following acute treatment, suggesting greater durability for CBT-SAD.


  • Cognitive behavioral therapy is generally considered safe for most people.

St. John’s Wort

There is limited evidence that St. John’s wort may improve some symptoms of SAD; however, the studies have been small.

What Does the Research Show?

  • A 2018 review of the following two trials concluded that there is currently no supportive evidence for any specific herbal intervention to confidently treat SAD.
    • A 1994 study of 20 participants who received St. John’s wort combined with either bright light or dim light therapy found significant reductions in depressive symptoms in both groups, but no significant difference between the two groups.
    • A 1999 study of 168 participants with SAD examined the effects of St. John’s wort on depressive symptoms and compared results to St. John’s wort plus light therapy. Improvement in symptoms were seen in both groups, with no significant differences between them.


  • St. John’s wort can weaken the effects of many medicines, including antidepressants, contraceptives, cyclosporine, digoxin, indinavir, irinotecan, and anticoagulants.
  • Taking St. John’s wort with certain antidepressants or other drugs that affect serotonin may lead to increased serotonin-related side effects, which may be potentially serious.
  • St. John’s wort may cause increased sensitivity to sunlight. Other side effects can include anxiety, dry mouth, dizziness, gastrointestinal symptoms, fatigue, headache, or sexual dysfunction.


Patients with SAD experience an aberrant seasonal variation in their light/dark nocturnal melatonin profile. The shorter photoperiod in winter causes delayed inhibition of morning melatonin secretion in patients with SAD but not in healthy individuals.

There is some limited evidence (small trials involving few patients) that suggests melatonin improves sleep in some patients with SAD; however, no definite conclusions about its effectiveness can be made.

What Does the Research Show?

  • A 2018 systematic review concluded that the few trials of melatonin for SAD suggest no place for this supplement as a treatment for SAD, but further investigation is need to draw definite conclusions.
  • A 2015 Cochrane review found no available methodologically sound evidence indicating that melatonin is or is not an effective intervention for prevention of seasonal affect disorder and improvement of patient-centered outcomes among adults with a history of seasonal affect disorder.
  • A 2003 controlled study conducted in Europe in 58 participants with SAD or weather-associated mood changes found significant improvements in quality of sleep and vitality in the SAD group; however, melatonin was ineffective in the weather-associated mood group.


  • Melatonin appears to be safe when used short-term, but the lack of long-term studies means we don’t know if it’s safe for extended use.
  • Side effects of melatonin are uncommon but can include drowsiness, headache, dizziness, or nausea. There have been no reports of significant side effects of melatonin in children.

Vitamin D

At present, vitamin D supplementation by itself is not considered an effective SAD treatment. Low blood levels of vitamin D are often found in people with SAD; however, the evidence for its use has been mixed. Although some studies suggest vitamin D supplementation may be as effective as light therapy, others found vitamin D had no effect.

What Does the Research Show?

  • A 2014 randomized controlled trial of 34 health care professionals failed to demonstrate an effect of vitamin D on SAD symptoms, but the study authors noted that the findings may be limited by confounders.
  • A 2006 randomized trial of 2,117 older women found that daily supplementation of vitamin D did not lead to an improvement in mental health scores.
  • A 1999 study of 15 participants compared vitamin D and broad spectrum phototherapy in the treatment of SAD. Participants receiving vitamin D improved in all outcome measures, while the phototherapy group had no significant change in depression scale measures.


  • High doses of vitamin D may cause fatigue, abdominal cramps, nausea, vomiting, renal damage, and other adverse effects.


  • Cools O, Hebbrecht K, Coppens V, et al. Pharmacotherapy and nutritional supplements for seasonal affective disorders: a systematic review. Expert Opin Pharmacother. 2018;19(11):1221-1233.
  • Dumville JC, Miles JN, Porthouse J, et al. Can vitamin D supplementation prevent winter-time blues? A randomised trial among older women. J Nutr Health Aging. 2006;10(2):151-153.
  • Frandsen TB, Pareek M, Hansen JP, et al. Vitamin D supplementation for treatment of seasonal affective symptoms in healthcare professionals: a double-blind randomised placebo-controlled trial. BMC Res Notes. 2014;7:529.
  • Gloth FM 3rd, Alam W, Hollis B. Vitamin D vs broad spectrum phototherapy in the treatment of seasonal affective disorder. J Nutr Health Aging. 1999;3(1):5-7.
  • Kaminski-Hartenthaler A, Nussbaumer B, Forneris CA, et al. Melatonin and agomelatine for preventing seasonal affective disorder. Cochrane Database of Systematic Reviews. 2015;11:CD011271.
  • Leppämäki S, Jaukka J, Lönnqvist J, et al. Drop-put and mood improvement: a randomised controlled trial with light exposure and physical exercise. BMC Psychiatry. 2004;4:22.
  • Leppämäki S, Partonen T, Vakkuri O, et al. Effect of controlled-release melatonin on sleep quality, mood, and quality of life in subjects with seasonal or weather-associated changes in mood and behavior. Eur Neuropsychopharmacol. 2003; 13(3):137-145.
  • Martinez B, Kasper S, Ruhrmann S, et al. Hypericum in the treatment of seasonal affective disorders. J Geriatr Psychiatry Neurol. 1994;1(Suppl 1):S29-S33.
  • Nussbaumer B, Kaminski-Hartenthaler A, Forneris CA, et al. Light therapy for preventing seasonal affective disorder. Cochrane Database of Systematic Reviews. 2015;11:CD011269.
  • Partonen T, Vakkuri. O, Lamberg-Allardt C, et al. Effects of bright light on sleepiness, melatonin, and 25-hydroxyvitamin D(3) in winter seasonal affective disorder. Biol Psychiatry. 1996 May 15;39.
  • Rohan KJ, Meyerhoff J, Ho S-Y, et al. Outcomes one and two winters following cognitive-behavioral therapy or light therapy for seasonal affective disorder. Am J Psychiatry. 2016;173:244-251.
  • Sarris J. Herbal medicines in the treatment of psychiatric disorders: 10-year updated review. Phytother Res. 2018;32(7):1147-1162.
  • Wehr TA, Duncan WC, Sher L, et al. A circadian signal of change of season in patients with seasonal affective disorder. Arch Gen Psychiatry. 2001;58(12):1108–1114.
  • Wheatley D. Hypericum in seasonal affective disorder (SAD). Curr Med Res Opin. 1999;15(1):33-37.
  • Wileman SM, Eagles JM, Andrew JE, et al. Light therapy for seasonal affective disorder in primary care: randomised controlled trial. Br J Psychiatry. 2001;178:311-316.

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