Sometimes known as the “winter blues,” people most commonly experience Seasonal Affective Disorder, or SAD, during the fall or winter, when days grow shorter and there is less direct sunlight. Research has supported the use of light therapy in treating SAD, but the precise biochemical relationship between the onset and treatment of SAD remains unclear. There appear to be four key biochemical markers of SAD.
Serotonin is a neurotransmitter in the brain. Levels appear to vary according to the amount of daily sunlight. In “Winter Blues: Everything You Need to Know to Beat Seasonal Affective Disorder,” Dr. Norman Rosenthal summarizes a collection of studies examining the role of serotonin in SAD. Dr. Rosenthal was the first researcher to describe SAD. People with SAD often crave carbohydrates such as sweets and starches; increased carbohydrate consumption appears to raise serotonin levels in the brain, offering support for a relationship with SAD. When people with SAD received light therapy, administering drugs that lowered serotonin levels appeared to undo light therapy treatment gains. For these reasons, antidepressants such as SSRI’s that increase serotonin levels may help to alleviate SAD.
SSRI’s aren’t the only class of antidepressants that affect SAD. Another antidepressant, Bupropion, that has been found to help with SAD, increases levels of dopamine in the brain. Dopamine is a neurotransmitter associated with response to pleasurable experiences.
In addition to dopamine, Bupropion increases levels of the neurotransmitter norepinephrine, which may also alleviate symptoms of SAD. Norepinephrine increases secretion of melatonin, which research has been implicated in SAD. Because neurochemical processes are so complex, it’s possible that levels of serotonin, dopamine, and norepinephrine all work in concert in creating or reducing SAD symptoms. All three are influenced by light therapy, the treatment of choice for SAD.
Melatonin is a naturally occurring chemical that helps to regulate the sleep-wake cycle. Secretion of melatonin increases during dark periods and decreases during light exposure. Research has found an association between melatonin levels and SAD, although the precise relationship between the two is not entirely clear.