Aerobic exercise: physical activity that requires extra effort of the heart and lungs to meet the body’s increased demand for oxygen; examples include running, swimming, cycling, and vigorous dancing.
Biochemistry: the chemistry of living organisms and life processes.
Bipolar disorder: also known as manic depression, this disorder involves mood swings that soar to mania, or unusual elation, and then plummet to Depression.
Dysthymia: a chronic (ongoing), low-grade depression that often begins in childhood or adolescence and may last for many years in adulthood if not treated.
Neurotransmitters: chemical messengers that carry messages or signals between the various nerves in the brain; the neurotransmitters serotonin, dopamine, and norepinephrine are believed to be the chemical messengers responsible for moods and emotions.
Retina: a 10-layered tissue membrane of the eye that transmits visual impulses through the optic nerve to the brain.
Seasonal Affective Disorder (SAD): a form of depression thought to be triggered by a decrease in exposure to sunlight.
Seasonal affective disorder (also called SAD) is a type of depression that follows the seasons. The most common type of SAD is called winter depression. It usually begins in late fall or early winter and goes away by summer. A less common type of SAD, known as summer depression, usually begins in the late spring or early summer. It goes away by winter. SAD may be related to changes in the amount of daylight during different times of the year.
Causes, incidence, and risk factors
The cause of seasonal affective disorder (SAD) is not known, but is thought to be related to the body’s temperature and hormone regulation. The disorder is rare, and most people with the “winter blahs” or cabin fever do not have SAD. The disorder may have its onset in adolescence or early adulthood, and it occurs more frequently in women than in men.
Revision date: July 5, 2011
Last revised: by Janet A. Staessen, MD, PhD