Psychobiology of Seasonal Affective Disorder

Biological Clock

Seasonal Affective Disorder (SAD) occurs at the same time each year. Most people experience this depression in the fall and into the winter months. They feel as if their energy is drained and become very moody. SAD also happens to people in the spring or early summer, although this is a less common type of SAD. People may experience mood changes when the seasons change. It is not known what causes the seasonal disorder, but it is believed that hormone levels and the body’s rhythm are involved. The reduced amount of sunlight in fall and winter may disrupt the body’s internal clock, which is your key to knowing when to sleep and wake up. The disruption of your circadian rhythm, or pattern over a 24-hour period, may result in depression, according to the Mayo Clinic. The levels of melatonin, a hormone that helps you to sleep, may become unbalanced during the changes in seasons. Reduced sunlight may also cause the drop in levels of serotonin, a brain chemical or neurotransmitter. This may lead to depression.


SAD appears to be more common among people who live far north or south of the equator. It is believed this is due to decreased sunlight during the winter and the longer days of summer. In the U.S., it is much more common in the northern states. People with winter SAD share a common trait in their reaction to changes in environmental light, according to the National Alliance on Mental Illness. Patients report longer and more profound depression the farther north they live. Depression can be mild or moderate. Some symptoms are severe, causing people to sleep too much, have little energy and crave sweets and starchy foods, says the National Institutes of Health. The depression usually clears up over time. Few SAD patients require hospitalization.

Gloomy Days

SAD patients also report their depression gets worse or reappears during days that are overcast at any time of the year. The mood may also be effected if their indoor lighting is decreased. Light therapy seems to be a major treatment in the fight against SAD. The patient sits a few feet from a light therapy box that provides exposure to bright light. The light is similar to outdoor light and may change brain chemicals linked to moods and it appears to be helpful. But researchers are still not sure how effective it is in treatment of SAD, just as they are not certain what causes the disorder.


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