Synopsis

Seasonal Affective Disorder (SAD) is a type of depression that occurs at specific times of the year, most commonly in the fall and winter months when daylight hours are shorter. It is linked to reduced sunlight exposure, which can disrupt circadian rhythms and lower serotonin and melatonin levels—neurochemicals vital to mood regulation and sleep. SAD leads to symptoms such as persistent low mood, fatigue, oversleeping, carbohydrate cravings, weight gain, and social withdrawal. A less common form, known as summer-pattern SAD, can cause anxiety and insomnia during warmer months. While SAD is more common in colder climates and higher latitudes, it is treatable with light exposure, supplementation, and lifestyle adjustments.

Types:

• Winter-pattern SAD: Most common, with symptoms appearing in late fall or winter

• Summer-pattern SAD: Less common, symptoms triggered by heat or extended daylight

Common Causes:

• Decreased sunlight exposure leading to melatonin overproduction and serotonin deficiency

• Disrupted circadian rhythms due to shorter days

• Vitamin D deficiency during darker months

• Genetic predisposition to mood disorders

• Preexisting depression or bipolar disorder

Severity Causes:

• Lack of morning light exposure or outdoor activity

• Chronic stress, isolation, or poor sleep hygiene

• Nutritional deficiencies (vitamin D, B vitamins, omega-3s)

• Coexisting depression, anxiety, or hypothyroidism

When to See a Doctor:

• Depressed mood that returns each year in a seasonal pattern

• Sleep disturbances and fatigue interfering with daily function

• Cravings, overeating, or significant weight changes

• Suicidal thoughts or worsening depression

• No improvement with light exposure or self-care efforts

Variant names

Seasonal depression
Winter-onset depression
Light deficiency disorder