When Does Seasonal Affective Disorder Typically Occur?
Seasonal affective disorder (SAD) typically occurs during autumn or winter months, with symptoms beginning in fall and continuing through winter, followed by full remission in spring or summer. 1
Temporal Pattern
The characteristic timing of SAD follows a predictable seasonal cycle:
- Onset: Symptoms typically begin in autumn (fall) as daylight hours decrease 2, 3
- Peak: Depression continues throughout winter months when daylight is shortest 1
- Remission: Full symptom resolution occurs in spring or summer as daylight hours increase 2, 4
Clinical Timing for Treatment Initiation
Based on the most recent guideline evidence, the temporal pattern has important treatment implications:
Preventive treatment should begin in September, or at least 2-4 weeks before the expected onset of depressive symptoms each year 1. This proactive approach allows clinicians to intervene before the full depressive episode develops.
For established SAD, treatment should be initiated in autumn with first onset of symptoms and continued through the winter months until spring or summer returns 1. Discontinuing treatment during winter frequently leads to relapse, so continuation throughout the entire at-risk season is essential.
Diagnostic Requirements
The temporal nature is so fundamental to SAD that diagnosis requires:
- Two consecutive years of episodes occurring in the same season 2
- Full remission when the specified season ends 2
This strict temporal criterion distinguishes SAD from non-seasonal depression and ensures the diagnosis reflects true seasonal variation rather than coincidental timing.
Less Common Variant
While the vast majority of SAD occurs in fall/winter, a less common variant causes depression in spring or early summer 3. However, this represents a minority of cases, and the winter pattern remains the defining characteristic of SAD.
Geographic Considerations
The prevalence and severity of SAD correlates with latitude, ranging from 1.5% to 9% depending on distance from the equator 5. Those living farther north experience more pronounced seasonal light variation and correspondingly higher SAD rates 2.