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People with seasonal affective disorder (SAD) instinctively shift
their melatonin levels with the seasons, paralleling the hibernation
patterns of mammals.
This does not appear to be true for those who don't react to shorter
days and longer nights with deepening depression.
In patients who had SAD, the duration of melatonin secretion became
longer in winter and shorter in summer, just as it occurs in other
mammals. That could be controlling this
panoply of changes that occurs in people when they get depressed
in the winter.
Seasonal affective disorder, or "winter depression,"
is a psychiatric disorder that strikes during winter months, when
daylight hours are naturally shortened. The disorder in humans seems
to mimic the behavior exhibited by hibernating animals, such as
increased sleep and decreased activity.
Melatonin, a hormone produced by the pineal gland in response
to the darkness of nighttime, promotes sleep and helps regulate
the body clock. Hibernation in mammals is triggered when the brain
responds to the body's increase in melatonin production.
Prior research suggests that people with
seasonal affective disorder are unable to use artificial light to
readjust their body clock, but remain susceptible to the seasonal
rhythms of shorter daylight hours during wintertime.
Healthy individuals were immune to shifts in the natural daylight,
with their melatonin levels remaining stable throughout the seasons.
However, those with winter depression
had a moderate decrease in the length of time they produced melatonin
during the summertime.
The duration of active melatonin secretion was about 9 hours in
the control group, whether in winter or summer. In the SAD group,
active melatonin secretion was 9 hours in winter and 8.4 hours in
summer.
Archives of General Psychiatry
December 2001;58:1108-1114
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