As humans, we spend roughly a third of our lives
asleep. When there is natural light we wake up, and at night we feel drowsy. This
phenomenon is called the body's "day and night" cycle or the circadian rhythm. Circadian rhythms control how we sleep, and when we wake up. They are managed by the
rise and fall of certain chemicals such as the hormones melatonin and cortisol,
and the neurotransmitter adenosine. Melatonin for example is sensitive
to light, increases with darkness, and helps us to settle into a deep sleep.
Cortisol spikes in the middle of the night and causes REM sleep - the phase where we
dream — and then wakes us up. Adenosine builds up during the day, gradually reduces our
alertness, and eventually makes us feel tired. Over 24 hours: with someone sleeping from
10 pm to 7 am the changes in melatonin, cortisol, and adenosine, typically look like this. Now while people all have different circadian
rhythms, known as different chronotypes, the rhythm itself shifts as we grow up and age. Children are typically born with an early
circadian rhythm, but when they enter puberty, their melatonin and cortisol kick in later, and
as a result their bodies react less to light and get sleepy about 2 hours later. They enter
into what's known as a delayed sleep phase. And since most schools don’t adapt to this change, teenagers end up sleeping less during
weekdays, and more during weekends — a phenomenon known as social jet lag. And
this leads to all kinds of problems. When teenagers lack rest, their minds have trouble
paying attention and absorbing new knowledge, and they often cannot remember what
they have learned during the day. This is because sleep is essential for consolidating
our experiences into our long-term memory store. Teenagers naturally go through a period of lots
of new sensations and often face an identity crisis. Now people who sleep less, naturally also
have less REM sleep — the phase where we dream, and that helps us regulate emotions.
Those who don’t get enough of that might get extra sensitive, moody, or
fail to understand their own feelings. A lack of rest leads to more stress during
the day, which in turn can mean insomnia at night - a vicious cycle that can hit adolescents
who are naturally more tense. In the best case, the stress impairs their creativity. At worst, it
leads to anxiety or addictions. This may be one reason why research shows that teenage suicide
rates go up when a new school year starts. Sleep also regulates the hormones
responsible for our appetite. And so, when teenagers don’t rest enough at night, they tend to eat more during the day. The
result can be obesity or eating disorders. The solution could be simple: adapt social
norms to biological facts and allow teenagers to sleep according to their natural circadian
rhythm. And some schools have done just that. In the fall of 2015, Seattle public schools
announced that it would change the school starting time from 7:50 AM to 8:45 — to adapt to
the circadian rhythm of teenagers. The result: pupils gained on average over 30 minutes
of sleep each night. Later they displayed higher concentration levels, reported better
wellbeing, and increased motivation to learn. What do you think? Should high schools
adapt to the biological rhythm of the pupils who go there? How has your
sleep cycle evolved and impacted your life? Tell us your thoughts and
experiences in the comments below! If you like this video and want us to make more,
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