Seasonal Affective Disorder

Seasonal affective disorder (SAD) is recurrent major depression with a regular seasonal pattern, usually autumn and winter onset with spring remission, for at least 2 consecutive years.

• Prevalence 1 to 10% depending on latitude; women predominate (4:1); onset in young adults.
• Mechanisms: circadian phase delay, melatonin dysregulation, reduced serotonin transporter function in winter.
• Atypical symptoms: hypersomnia, hyperphagia, carbohydrate craving, weight gain.
• Summer pattern is rarer.

• Low mood, lethargy, oversleeping, increased appetite and weight, social withdrawal, reduced concentration, anhedonia, with spring resolution (or hypomania).
• Distress and impaired work.
• Suicidality can occur.

• DSM-5 specifier (with seasonal pattern); Seasonal Pattern Assessment Questionnaire.
• Exclude bipolar disorder, hypothyroidism, vitamin D deficiency, substance misuse, sleep apnoea, adjustment to seasonal stressors.
• TSH, full blood count, vitamin D.

• Bright light therapy: 10,000 lux light box for 30 minutes within an hour of waking, from early autumn through spring; response in 50 to 80% within 1 to 2 weeks; eye examination if retinal disease, caution in bipolar disorder.
• CBT for SAD (6 to 12 sessions) has sustained benefit.
• Antidepressants: sertraline 50 to 200 mg, escitalopram 10 to 20 mg, fluoxetine 20 to 60 mg; bupropion XL 150 to 300 mg started in autumn prevents recurrence.
• Vitamin D 1000 to 2000 IU if deficient, outdoor activity, regular sleep.
• Treat as major depression when severe; review annually before autumn.