Seasonal Affective Disorder is depression that follows a predictable seasonal pattern — typically winter onset, spring/summer remission. About 5% of U.S. adults have SAD; another 10-20% experience milder seasonal mood changes that don’t meet full criteria.
SAD has identifiable biology involving circadian rhythm disruption, melatonin patterns, and serotonin function — and several evidence-based treatments that work specifically for the seasonal pattern.
What SAD Actually Is
SAD is a subtype of major depression with a seasonal pattern. Diagnostic criteria require:
- At least 2 consecutive years of depressive episodes occurring during the same season
- Full remission (or shift to hypomania/mania in bipolar pattern) at the other end of the seasonal cycle
- Seasonal episodes substantially outnumbering non-seasonal episodes lifetime
Symptoms — often atypical
SAD frequently presents with atypical depression features:
- Hypersomnia — sleeping more, finding it hard to wake
- Increased appetite, particularly for carbohydrates
- Weight gain
- Marked fatigue
- Social withdrawal
- Low mood with reactivity (briefly improved by positive events)
This differs from typical major depression, which more commonly involves insomnia, decreased appetite, and persistent mood without reactivity.
The Biology
SAD involves several interacting factors:
- Circadian rhythm disruption — reduced winter daylight delays melatonin offset, leaving patients feeling like it’s still nighttime in the morning
- Melatonin patterns — both duration and timing of melatonin secretion are altered
- Serotonin function — lower light exposure correlates with decreased serotonin activity
- Vitamin D — lower winter levels may play a role for some patients
- Genetic susceptibility — SAD runs in families
Evidence-Based Treatment
Light therapy
Bright light therapy is first-line and highly effective. Standard protocol: 10,000 lux light box, 20-30 minutes daily, ideally first thing in the morning, eyes open but not staring directly into the light. Improvement typically begins within 1-2 weeks. Best evidence supports starting in fall before symptoms develop and continuing through winter.
SSRIs
Bupropion XL has FDA approval specifically for prevention of SAD episodes — started in autumn before symptoms emerge. Other SSRIs and SNRIs are effective for treatment of SAD episodes once they develop.
Other approaches
CBT specifically adapted for SAD (CBT-SAD) is effective. Maintaining outdoor light exposure when possible matters. Vitamin D supplementation if deficient. Sleep regularity supports recovery.
Source: Lam et al., American Journal of Psychiatry.
When to Start Treatment
For patients with confirmed SAD, starting treatment in early fall — before symptoms emerge — is more effective than waiting until symptoms become severe. This is true for both light therapy and bupropion XL (FDA-approved specifically for this prevention).
“Just winter blues”
SAD often gets dismissed as normal winter mood — leaving patients to suffer through 4-6 months annually with treatable depression.
Proactive seasonal care
Dr. Farkas identifies SAD patterns and initiates evidence-based treatment — often starting before symptoms emerge each fall.
Winter without depression
Most SAD patients can have substantially normal winters with combination treatment — reclaiming several months of life each year.
Common Questions About SAD
Can I have summer SAD?
Yes — summer-pattern SAD exists but is less common than winter pattern. Often presents with insomnia, decreased appetite, agitation rather than the winter pattern’s hypersomnia and increased appetite.
Will I always have SAD?
SAD often continues year after year if untreated, but treatment is effective. Some patients reduce treatment over time; others maintain it long-term.
Does moving south help?
Often yes — geographic latitude correlates with SAD prevalence. Many patients improve substantially when relocating to lower latitudes. Hilton Head’s latitude (32°N) is helpful for many SAD patients moving from northern locations.
Does taking vitamin D help?
If you’re deficient, yes. Vitamin D supplementation isn’t a substitute for established SAD treatments but addresses one contributing factor. See our related article on major depression.