Seasonal Affective Disorder (SAD)

Seasonal Affective Disorder (SAD) is a type of depression that follows a seasonal pattern. Most commonly, symptoms begin in fall, worsen through winter, and resolve in spring—known as "winter-pattern SAD" or "winter depression." **Key features:** - Recurrent depressive episodes with seasonal pattern - Full remission (or switch to mania in bipolar) at characteristic time - Seasonal episodes substantially outnumber non-seasonal episodes - Must occur for at least 2 consecutive years **Winter-pattern SAD symptoms:** - Oversleeping (hypersomnia) - Overeating, especially carbohydrate craving - Weight gain - Social withdrawal ("hibernating") - Low energy, fatigue - Depressed mood **Summer-pattern SAD** (less common): - Insomnia - Poor appetite, weight loss - Agitation and anxiety - Episodes of violent behavior **SAD vs. Winter Blues:** Many people feel some mood change in winter. SAD is diagnosed when symptoms are severe enough to significantly impair functioning and meet criteria for major depression.

SAD is related to changes in light exposure: **Biological mechanisms:** **Circadian rhythm disruption:** - Reduced light in winter affects the body's internal clock - Delayed circadian rhythms (phase shift) - The brain does not properly adjust to shorter days **Melatonin:** - Darkness increases melatonin (sleep hormone) - Longer nights = more melatonin = sleepiness and lethargy - People with SAD may overproduce melatonin **Serotonin:** - Reduced sunlight can lower serotonin levels - Serotonin affects mood, and low levels are linked to depression - Carbohydrate craving may be an attempt to boost serotonin **Vitamin D:** - Reduced sunlight exposure decreases vitamin D production - Low vitamin D is associated with depression - May be an additional contributing factor **Risk factors:** - Living far from equator (higher latitudes) - Family history of SAD or depression - Having depression or bipolar disorder - Younger age - Female gender