Description

• Patients experience depressive episodes 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. Conversely, patients may experience a spring-summer onset with remission in fall-winter months, although this is less common.
• Ranges from a seriously disabling illness to milder subclinical symptoms colloquially termed “winter blues”

Epidemiology

Etiology and Pathophysiology

• Photoperiod and phase shift hypotheses: 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, causing a misalignment of the circadian rhythm from the sleep-wake cycle. 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, although vitamin D’s role appears more correlation than causation.
• Serotonin dysregulation hypothesis: This hypothesis poses there is increased serotonin transporter activity leading to enhanced clearance from the synaptic cleft. This altered secretion is thought to contribute to seasonal affective disorder (SAD) pathophysiology. Centrally acting serotonergic agents, such as SSRIs, have been shown to alleviate SAD symptoms.

Risk Factors

• Most common during months of January and February
• Spending a prolonged period of time in an environment without windows or significant sunlight exposure
• Living at a higher latitude

General Prevention

• 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.
• The role of low-dose evening melatonin as prevention is not definitively established, with studies showing mixed results. It may have a role in symptom management (see “Treatment”).

Commonly Associated Conditions

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