Seasonal Affective Disorder: Blame It on Sunlight and Serotonin

SAD The winter blues are not just a frame of mind; they are also a state of mind. Seasonal affective disorder (SAD) is characterized by a drop in energy level, fatigue, difficulty concentrating, irritability, weight gain, and carbohydrate cravings, among other symptoms. It usually begins by late fall or early winter and ends by late spring or early summer. The neurotransmitter serotonin is believed to play a significant role in SAD.

It Is (and Isn’t) All in Your Head

Although scientists have long suspected an important role for serotonin in SAD, concentrations of this neurotransmitter in the cerebrospinal fluid bathing the brain and spinal cord of people with SAD appear to be normal.In an article published in The Lancet, researchers from the Baker Heart Research Institute in Australia sought to determine whether concentrations of serotonin and other neurotransmitters measured from blood vessels draining the brain (a more accurate measure of serotonin concentrations in the brain than cerebrospinal fluid) would provide evidence for the relationship between serotonin and SAD. In this study, researchers enrolled 101 healthy men between the ages of 18-79 years old. None of the men included in the study had a history of major illness (including depression ) or cardiovascular disease, were currently on any medication, or had previous psychiatric therapy. Over the course of a year, the researchers gained access to blood draining from the brain of the volunteers by taking samples from their internal jugular veins, which are found in the neck. They then measured the blood concentrations of serotonin and two other neurotransmitters not believed to be directly related to SAD—dopamine and norepinephrine—to use as controls. The neurotransmitter concentrations were then correlated to seasonal factors (measured daily), such as highest and lowest temperatures, total rainfall, and hours of bright sunlight. As expected, production of serotonin by the brain was lowest in winter and was strongly correlated with the amount of bright sunlight during the day. Other than bright sunlight, no other seasonal factors had an effect on serotonin production. Concentrations of dopamine and norepinephrine were not influenced by these factors.The major limitation of this study is that it was conducted on healthy volunteers, and it is not known whether environmental factors would affect people with SAD in the same way.

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