New research confirms 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
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.
This work was presented at the European
College of Neuropsychopharmacology (ECNP) congress in Berlin.
SAD affects a significant amount of people as daylight
levels drop in autumn. At Northern European latitudes (for example all of
Scandinavia, Glasgow and Moscow) around 1 person in 6 suffers from SAD.
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.
Serotonin (also known as 5-HT) is a neurotransmitter which
affects mood, in fact many anti-depressant drugs, such as SSRIs
(Selective Serotonin Reuptake Inhibitors, such as Prozac) work by allowing
serotonin to be retained in the synapse where it exerts its
Lead researcher, Brenda Mc Mahon said, "We believe that we
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 SAD patients had an average 5% higher SERT level in the
winter compared to the summer, whereas the healthy participants on average
showed no significant change.
Commenting for the ECNP, Professor
Siegfried Kasper (Vienna) said, "SERT fluctuations associated with SAD
have been seen in previous studies, but this is the first study to follow
patients through summer and winter comparisons. It seems to offer confirmation
that SERT is associated with SAD."