BIOCHEMICAL CAUSE OF SEASONAL DEPRESSION CONFIRMED
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 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. This work is being presented at the 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
effects.
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"
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