Seasonal Depression – Biochemical Cause Confirmed

Seasonal depression, also known as seasonal affective disorder (SAD), is a form of depression that’s associated with changes in season. This phenomenon typically begins in the fall and continues into the winter months. Those who are affected by SAD report feeling moody and depleted of energy during winter months. Classified as a subtype of major depression, SAD causes symptoms like loss of appetite, difficulty concentrating, and fatigue. Until recently, the biological cause of SAD was unknown. However, new research from the European College of Neuropsychopharmacology has uncovered a biochemical link to SAD.

The study found that those who suffer from winter blues regulate serotonin differently than those who do not suffer from SAD. Serotonin is a neurotransmitter that has several functions – but is known for contributing to feelings of well being and happiness. Serotonin has considerable effects on mood. In fact, most anti-depressant drugs work by affecting serotonin levels in the brain. The study consisted of 11 people with SAD, and 23 individuals unaffected by SAD. The researchers scanned the participants using positron emission tomography (PET), which produces three-dimensional images of the body. The PET scans revealed significant differences from summer to winter in terms of serotonin transporter (SERT) protein levels. Patients with SAD tend to have higher levels of SERT during winter months, which means serotonin is being removed at higher levels during this time. The serotonin transporter is responsible for carrying serotonin back to the nerve cells when it’s not active. The higher the SERT activity, the lower the serotonin activity.

The researchers believe they’ve discovered the brain dial that’s used when it has to adjust serotonin according to changing seasons. The real reason behind all of this serotonin adjuster is sunlight. Sunlight is directly linked to mood enhancement. Even large-scale studies show that people who live in areas of the world with less sunlight tend to be more depressed. For example, depression levels in Seattle tend to be higher than in sunny cities. Sunlight keeps the SERT activity low, and in turn, serotonin activity is heightened. When nights grow longer in autumn and winter, SERT levels naturally increase, causing serotonin levels in the brain to diminish. While this phenomenon occurs in everyone, only some are negatively impacted in the form of seasonal depression. In those with SAD, researchers explain that this group experiences an increase in SERT activity that remains high throughout the winter. In fact, SAD patients have an average of 5% higher SERT levels in the winter compared to the summer. Healthy participants in the study, however, showed no significant change in SERT activity throughout the seasons. While previous studies have proven the fluctuations in SERT activity in participants with seasonal depression, this study was the first to follow the participants in order to do seasonal comparisons – and it was the first to focus on SERT’s role in seasonal depression. This finding could lead to additional therapies relevant in both the prevention and treatment of seasonal depression, and possibly other types of psychological disorders.


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