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Mood Changes Linked To Seasonal Fluctuations in Serotonin

Natalie Staats Reiss, Ph.D. Updated: Sep 9th 2008

person walking alone in fogA new research study published in the September issue of the Archives of General Psychiatry suggests that there is a biological link between the season of the year, and our mood and energy level. 

Canadian researchers studied 88 healthy people using Positron Emission Tomography (PET) scans. PET scans provide both two- and three-dimensional pictures of brain activity by measuring radioactive isotopes (elements that attach to chemicals that flow through the brain) that are injected into the bloodstream. After the isotope is injected into the bloodstream, overhead sensors register the isotope's activity. The collected information is processed by a computer and displayed on a monitor or film.

In the current study, the PET scans were used to measure serotonin binding potential. Serotonin is a neurotransmitter (a chemical messenger that carries information throughout the brain and nervous system) that is involved in regulating many important physiological (body-oriented) functions, including sleep, aggression, eating, sexual behavior, and mood. Using information about serotonin binding potential, the researchers were able to assess serotonin transporter density. Serotonin transporters remove serotonin from the system, so the higher someone's serotonin binding potential, the less serotonin that is circulating in the brain.

To study seasonal fluctuations of serotonin binding potential, the researchers grouped the participants' PET scans according to the season of the year-- fall/winter or spring/summer. The serotonin binding potentials were significantly higher during the fall and winter months than in the spring and summer. So, results suggest that there is more serotonin removal (and less serotonin circulating in the brain) during the darker, colder time of the year.

Seasonal decreased serotonin levels are linked to decreased mood and increased lethargy.  In addition, in some people, low serotonin levels can cause depressive symptoms, Seasonal Affective Disorder (a diagnostic specifier used when a person's major depressive episodes occur regularly and coincide with a specific season of the year), and/or a suicidal mood state.

For more information about Depression, please see our related topic center. For more information about Seasonal Affective Disorder, please click here.  


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