In a paper
exploring circadian rhythms and start times for student classes, researchers
point out that the average biological wake time for kids at the age of 10 is
6:30am, at age 16 it is 8:00am, and at age 18 it is 9:00am. Reconciling these wake times with school
starting times, the researchers suggest that kids at the age of 10 would
ideally start school at 8:30-9:00am; at age 16, they would start at 10:00-10:30am;
and at age 18, they would start at 11:00-11:30am.
The paper bases these recommendations on advances over the
last three decades in sleep medicine and circadian neuroscience that have
provided a better understanding of the patterns of wakefulness and sleep that
hold sway over our lives.
The physiology and behavior of most life on earth exhibits a
24-hour rhythm linked to the day/night cycle.
This pattern is governed by a master circadian (24-hour) pacemaker
located in the suprachiasmatic nuclei (SCN) of the hypothalamus. The SCN receives signals from photoreceptors
in the eye, effectively linking our circadian rhythms to the environmental
day/night cycle. Behavioral, metabolic,
and physiological rhythms are all affected by the 24-hour cycle, including
alertness and performance, hormones, core body temperature, and rhythms in
organs such as the lungs, liver, and heart.
The sleep-wake cycle arises from the interaction of two
basic impulses we all experience: alertness and sleepiness. These instincts are generated by the SCN
pacemaker and a homeostatic sleep cycle which intensifies the pressure to go to
sleep with increasing time awake and dissipates this pressure as time asleep
accumulates. These processes work in
opposition to maintain a state of wakefulness during the day, and a state of sleep
during the night.
In adolescence, the timing of the circadian clock shifts
later, delaying the phase at which sleep can be initiated. The graph below is from a study
drawing on a survey of 25,000 people in Switzerland and Germany. It plots the chronotypes of the respondents
versus their ages. Chronotype refers to
when a person's internal circadian clock synchronizes to the 24-hour day. Starting in early childhood, chronotypes tend
to be early in the day - in other words, babies naturally wake up early. Through age 20, chronotypes rise to their
maximum - teens naturally wake up later in the morning. After age 20, chronotypes decline through old
age - as we get older, we tend to wake up earlier in the morning.

Chronotype vs. age from a survey of 25,000 people in Switzerland and
Germany.
Because circadian rhythms determine our optimal hours of
work and concentration, the researchers suggest that it makes sense to align
our working hours with our internal clocks.
Of course, every individual has a unique chronotype, and some 18 year
olds are perfectly comfortable waking up at 6am. But when setting class starting times for the
general population of students, perhaps school districts should take into
account circadian rhythms and chronotypes in an effort to make the most
efficient use of student's optimal waking hours, not to mention protecting
their wellness.
What do you think?
Should class start times be adjusted to fit the natural rhythm of
wakefulness?
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