Seasonal Affective Disorder

BASICS

Seasonal affective disorder (SAD) describes mood episodes that occur as a part of major depressive or bipolar disorder in a seasonal pattern. Patients experience depressive or, less commonly, hypomanic or manic episodes.
Depressive episodes typically occur during winter months (fall-winter onset), with full remission in the spring and summer. Oppositely, patients may experience a spring-summer onset with remission in fall-winter months, though this is less common.
Ranges from a milder form (known as winter blues) to a seriously disabling illness

Affects up to 500,000 Americans every winter
Up to 30% of patients visiting a primary care physician (PCP) during winter may report winter depressive symptoms.
Predominant age: occurs at any age; peaks in 20s and 30s
Predominant sex: female > male (3:1)

Photoperiod and phase shift hypothesis: During the winter months, the period of natural daylight is shorter. When there is less sunlight, the pineal gland increases melatonin secretion (photoperiod hypothesis). This can lead to a phase shift where circadian rhythm and sleep are misaligned. Light therapy in the morning or evening can suppress melatonin secretion to correct the phase shift and improve symptoms of depression. Reduced sunlight may also decrease vitamin D levels, which may contribute to symptoms of depression.
Serotonin dysregulation hypothesis is a suspected dysregulation of serotonin, particularly increased clearance from the synaptic cleft and reduced secretion, contributes to SAD pathophysiology. Central acting serotonergic agents such as SSRIs appear to reverse SAD symptoms.

Twin studies suggest a genetic component.
Studies also indicate an association with melanopsin gene (OPN4) and GPR50 melatonin receptor variants.

Most common during months of January and February
Working in a building without windows or other environments without significant sunlight exposure

Increase time outside during daylight hours, or move to, or plan to vacation at, a more southern location. Bright light therapy may be effective as treatment but has not been shown beneficial as preventative treatment.
Bupropion (Wellbutrin) is the only FDA-approved antidepressant for the prevention of SAD.
Although studies show mixed results, low-dose evening melatonin may help prevent symptoms of depression from occurring.

Comorbid psychiatric disorders such as alcohol use disorder, ADHD, and binge eating

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