Seasonal affective disorder (SAD) has several nicknames — winter depression, winter blues, and seasonal depression. It is a type of mood disorder that many people experience in the winter and typically goes away in the spring and summer.
About 6% of Americans, primarily those living in northern climates, experience SAD. Another 14% of adults suffer from the slightly milder form of seasonal depression — winter blues. Symptoms of SAD include weight gain, craving sweets and carbs, lack of energy, problems focusing, social withdrawal, fatigue, and a tendency to oversleep.
Doctors are not certain what causes seasonal depression, but several theories exist. One has to do with lack of sunlight. Less light means lower levels of Vitamin D, which is important for the production of serotonin, which controls many brain functions and behaviors. Another explanation has to do with melatonin, also known as the sleep hormone. Shorter days in the winter mean longer periods of darkness, which increases melatonin production, leaving people feeling more lethargic and tired.
A third theory has to do with people’s ability to regulate serotonin. Patients with SAD have 5% more serotonin transporter protein in winter months. This means there is less serotonin available because the function of the transporter is to recycle serotonin back into the presynaptic neuron, a nerve cell that releases neurotransmitters.
To identify ways to combat seasonal affective disorder, 24/7 Tempo reviewed dozens of studies about the condition, its effects on mental health, and potential treatments.