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What Causes Seasonal Affective Disorder?

joy Sep 17, 2020

Timothy Culbert, MD, IFMCP


SAD has been linked to a biochemical imbalances in the brain, likely involving melatonin and serotonin prompted by shorter daylight hours and less sunlight during the fall and winter months. As seasons change, people experience a shift in their internal 24-hour “clock” or circadian rhythm and may become “out of sync” with other mind/body rhythms. SAD is more common in populations living farther from the equator.

Melatonin and SAD

Melatonin is linked to sleep. It's produced in greater quantities when it's dark or when days are shorter. Increased production of melatonin can cause sleepiness and lethargy. 

Serotonin and SAD

The production of serotonin increases with exposure to sunlight. Low levels are associated with depression, so increasing the availability of serotonin helps to combat depression. Learn how to boost serotonin here.>>>

A 2009 article analyzes SAD from proposed biological and psychological mechanisms:

(Rohan, K. J., Roecklein, K. A., & Haaga, D. A. (2009). Biological and psychological mechanisms of seasonal affective disorder: a review and integration. Current Psychiatry Reviews5(1), 37-47.)

Proposed Biological Mechanisms of SAD

Environmental Stress. Environmental stress is higher in fall and winter months which might make us susceptible to SAD.

Circadian Rhythm Shift. Whether delayed or advanced, a shift in the circadian rhythm is related to the timing of melatonin release.

Retinal Light Sensitivity. Individuals with SAD are less sensitive to environmental light cues and may be less sensitive to the amount of  light that they receive year around.

Neurotransmitter Alterations. For most people, serotonin levels are generally lower in the winter and higher in the summer.  Fluctuations in norepinephrine (NE) and dopamine levels are also being explored:

  1. Learn about reducing Norepinephrine from our article, Disarm Yourself: Reduce Norepinephrine.>>>
  2. Learn about increasing dopamine from our article, Reward Yourself: Increase Dopamine.>>>

Genetic Influences. Certain genetic profiles have higher risk of SAD such as genes for circadian rhythm, serotonin, dopamine, and retinal photopigment differences.

Proposed Psychological Mechanisms of SAD

Cognitive Mechanisms. Acute or ongoing stressors and preexisting cognitive vulnerability to depression (rumination, dysfunctional attitudes, negative attributional style) interact to trigger symptoms of SAD.

Behavioral Mechanisms. Behavioral disengagement may serve as a vulnerability for depression onset or maintenance. Emotional and psychophysiological reactivity to light and other seasonally relevant cues may be another behavioral factor that influences SAD.

In their integrative approach the authors suggest that a given individuals psychological appraisals and expectations of fall/winter, together with the impact of changing environmental cues (light and temperature/weather); interact with psychological and biological vulnerabilities, potentially triggering SAD symptoms. 

Treatment for Seasonal Affective Disorder

SAD can be effectively treated in a number of ways, including light therapy (read our article on light therapy here), antidepressant medications, talk therapy, vitamins, supplements, exercise, mind/body skills training or some combination of these. For many people, symptoms will generally improve on their own with the change of season, however- improved daily functioning  can be more quickly restored with treatment.

Helpful conventional treatments can include talk therapy (particularly cognitive behavioral therapy) which can effectively treat SAD. From the medical standpoint, SSRIs (fluoxetine and sertraline have the best evidence) are the types of antidepressant medications most commonly used to treat SAD.

If you are a therapist/counsellor/psychologist seeing patients who you feel have symptoms of SAD, considering partnering with a trained medical professional to make sure there is no other medical condition causing the patient’s/client’s symptoms. SAD can be related to medical problems such as hypothyroidism, hypoglycemia, chronic illness, infectious mononucleosis, and other infections, so proper evaluation is key. 

Natural Approaches For SAD

For many individuals, natural therapy can be very effective for the treatment of SAD. More severe versions of SAD can be effectively treated in a number of conventional ways, including the use of antidepressant medications and talk therapy. At Natural Mental Health, we also have some ideas about holistic options for treating SAD.  While symptoms will generally improve on their own with the change of season, symptoms can improve more quickly with treatment.

There are some very effective natural therapies we can all utilize to help either prevent symptoms of seasonal affective disorder before they start, and/or treat symptoms of seasonal affective disorder if they have started for you. Of course, it’s best to prevent these symptoms by starting to do a few things right away beginning in late September and early October when the days begin shortening here in North America.

Some of the best things you can do to address symptoms of seasonal affective disorder can be found at our article, A Light on SAD: Definition, Treatment and Prevention.>>>

Aromatherapy and SAD

We often associated the use of essential oils by inhalation or topical application to the skin (also known as aromatherapy) with their ability to calm our mind and body. However, some essential oils have mood changing and energy enhancing qualities as well. These essential oil blends are among our favorites for helping symptoms of SAD:

Healing Alchemy Energizing Blend: contains essential oils of turmeric, rosemary, bergamot and peppermint to activate mind and body.

Healing Alchemy Uplifting Blend: contains essential oils of mandarin, bergamot and vetiver to balance your mood and shift to positive, renewing emotions.


Keep reading about natural techniques and preventative tools for SAD at our article, A Light on Seasonal Affective Disorder.>>> 



Stewart, Alan E., et al. 2014. Possible contributions of skin pigmentation and vitamin D in a polyfactorial model of seasonal affective disorder. Medical hypotheses 83.5: 517-525.

Miller, A. L. (2005). Epidemiology, etiology, and natural treatment of seasonal affective disorder. Alternative Medicine Review10(1).

Melrose, S. (2015). Seasonal affective disorder: an overview of assessment and treatment approaches. Depression research and treatment2015.

Menculini, G., Verdolini, N., Murru, A., Pacchiarotti, I., Volpe, U., Cervino, A., ... & Tortorella, A. (2018). Depressive mood and circadian rhythms disturbances as outcomes of seasonal affective disorder treatment: A systematic review. Journal of affective disorders.

Wehr, T. A., Duncan, W. C., Sher, L., Aeschbach, D., Schwartz, P. J., Turner, E. H., ... & Rosenthal, N. E. (2001). A circadian signal of change of season in patients with seasonal affective disorder. Archives of General Psychiatry, 58(12), 1108-1114.

Rohan, K. J., Roecklein, K. A., & Haaga, D. A. (2009). Biological and psychological mechanisms of seasonal affective disorder: a review and integration. Current Psychiatry Reviews5(1), 37-47.


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