Seasonal Depression: Understanding its Chemical Cause

The same time every year, some people across the globe suddenly find themselves severely depressed. This is called seasonal affective disorder (SAD) and it has left professionals scratching their heads for years. Now a team of researchers have discovered that SAD could be caused by increased levels of the serotonin transporter protein.

Past research has identified that less exposure to sunlight during the winter season could contribute to SAD, where vitamin D deficiency (sunlight is a primary source of the vitamin) can lead to fatigue and irritable mood. This sparked a health movement where natural light lamps and vitamin supplements become top sellers as the days grow shorter. However, the exact neuro-chemical cause of the SAD phenomenon remained a mystery.

Now, a team of University of Copenhagen researchers recently announced to their peers at the European College of Neuropsychopharmacology (ECNP) Congress in Berlin, Germany that they believe they have found the exact cause.

"We believe that we have found the dial the brain turns when it has to adjust serotonin to the changing seasons," lead researcher Brenda Mc Mahon said in a statement.

 "The serotonin transporter (SERT) carries serotonin back into the nerve cells where it is not active, so the higher the SERT activity the lower the activity of serotonin," she explained. "Sunlight keeps this setting naturally low, but when the nights grow longer during the autumn, the SERT levels increase, resulting in diminishing active serotonin levels. Many individuals are not really affected by SAD, and we have found that these people don't have this increase in SERT activity, so their active serotonin levels remain high throughout the winter."

In an assessment of people suffering from SAD, Mc Mahon and her colleagues found that depressed patients had an average 5% higher SERT level in the winter compared to the summer, whereas healthy participants on average showed no significant change.

In response to this study's release, Beth Murphy, the head of information at Mind, told Medical News Today that while knowing the chemical cause of SAD can provide some insight, many of the therapies already prescribed to patients are proven effective.

"Talking treatments, such as counseling, psychotherapy or cognitive behavior therapy (CBT) can be extremely useful in helping people to cope with symptoms," she said. "Antidepressants may be prescribed for people with severe SAD and can be combined with light therapy for maximum effect."