Why some of us suffer from 'winter blues' revealed

A new study has shed light on why some people suffer from the winter blues while others get through the winter without any problems.

A longitudinal study from a group of researchers from the University of Copenhagen has found that that people with Seasonal Affective Disorder (SAD) show significant seasonal differences in the way they regulate the neurotransmitter serotonin in comparison to the majority of the population.

The researchers scanned 11 SAD patients and 23 healthy individuals using Positron Emission Tomography; they were able to show significant summer to winter differences in the levels of the serotonin transporter (SERT) protein; SAD patients showed higher levels of SERT in the winter months, corresponding to a greater removal of serotonin in winter.

Lead researcher, Brenda Mc Mahon said that they believe that they have found the dial the brain turns when it has to adjust serotonin to the changing seasons. 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. 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.

The findings showed that the SAD patients had an average 5 percent higher SERT level in the winter compared to the summer, whereas the healthy participants on average showed no significant change.