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Seasonal Affective Disorder (SAD)

Characterized by the onset of depression during winter months with less natural sunlight, SAD is often accompanied by social withdrawal, increased sleep and weight gain. Symptoms may start out mild and become more severe as the season progresses. It generally lifts during spring and summer and predictably returns every winter.

More than a case of the “winter blues” or a seasonal funk that one has to deal with alone, SAD can be treated to keep mood and motivation steady throughout the year.

Causes of SAD remain unknown, but some factors may trigger depression:

Biological clock (circadian rhythm)—A reduced level of sunlight in fall and winter may disrupt the body’s internal clock. 

Drop in serotonin levels (a brain chemical or neurotransmitter that affects mood)—may be caused by reduced sunlight.

Melatonin levels—Season change can disrupt the balance of the body’s level of melatonin, which plays a role in sleep patterns and mood.

Risk factors for SAD include:

Family history. SAD is more common among those with blood relatives with SAD or another form of depression.

Having major depressive disorder or bipolar disorder. Symptoms of depression may worsen seasonally with one of these conditions.

Living far from the equator. SAD is more common among those who live far north or south of the equator, most likely due to decreased sunlight during and shorter days during the winter.

Low level of vitamin D. Since vitamin D—which boosts serotonin activity—is produced in the skin when exposed to sunlight, less sunlight can contribute to lower levels of vitamin D in the body.


Read more about evidence-based treatment options at CFI for Seasonal Affective Disorder and other mood disorders.



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