Biology Reference
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duration shortens drastically (by almost 2 h) from the age of 10 to
17 (
Fig. 11.3
A). The separate analysis for work and free days reveals, how-
ever, that this sharp decline is mainly due to work- or school-day sleep
(
>
2 h), while sleep duration on free days becomes only gradually shorter
from the age of 10 to retirement. The profound mismatch between the
“enforced” sleep duration on school/work days and free-day sleep duration
demonstrates the immense impact of social times on our daily sleep behavior.
Note that the mismatch disappears completely at around the average age of
retirement (65 years).
The differences in sleep between work and free days not only relate to
outside the temporal window provided by the circadian clock (e.g., naps),
sleep is more efficient, and SCRD minimized, when it coincides with this
interruption of sleep by the alarm clock on workdays (black bars in
can lead to a substantial sleep loss (see also
Fig. 11.3
). The main reason
for this sleep deficit is that the circadian clock strongly influences when
one can fall asleep (independent of sleep pressure, i.e., the homeostatic drive)
while the alarm clock artificially puts an abrupt end to sleep. To compensate
for this workday sleep debt, people commonly oversleep on free days (white
days resembles the situation of traveling across several time zones to theWest
on Friday evenings and “flying” back onMonday mornings, the term “social
symptoms of jetlag (e.g., problems in sleep, digestion, and performance) are
manifestations of a misaligned circadian system. In travel-induced jetlag,
they are transient until the clock reentrains. By contrast, social jetlag is
chronic throughout a working career.
The developmental changes in circadian timing discussed above, in com-
bination with the fact that school start times are suited to the predominantly
end of adolescence (
Fig. 11.5
). This is why teenagers show the largest dis-
crepancy in sleep duration between free days and workdays compared to all
other ages (
Fig. 11.3
).
Only 13% of the population represented in the MCTQ database is free of
social jetlag, 69% experience at least 1 h, and a third suffers from 2 h or more.
The discrepancy between biological (circadian) time and social time is a
major reason for sleep deprivation (SD). About 5% of
the database
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