WEBVTT

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So far, we've spoken about

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all of the wonderful
benefits that sleep provides,

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but how much sleep should
we actually be getting?

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[Sleeping with Science]

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(Music)

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For the average adult,
the current recommendation

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is somewhere between seven to nine
hours of sleep a night.

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And what we've been finding
from large-scale epidemiological studies

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is that, using that reference point
of seven to nine hours,

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once you start to drop below that,

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your mortality risk
actually starts to increase.

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In fact, the Center for Disease Control
in the United States, or the CDC,

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they stipulate a minimum
of seven hours of sleep a night

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for the average adult.

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In other words, the shorter your sleep,

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the shorter your life.

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But it turns out that it's not quite
a linear relationship as you would expect.

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It's not as though the more
and more that you sleep,

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the lower and lower
your mortality risk is.

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In fact, something strange happens.

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Once you get past nine hours,

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you actually start to see
a rise back up in mortality risk,

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which seems rather strange and peculiar.

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And scientists have actually put forward
at least two different explanations.

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The first is that,
if you look at those studies,

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it may be that individuals are suffering
from significant disease and illness.

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When we become infected,
or we have disease,

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typically, we try to sleep longer,
we stay in bed longer.

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So in other words,

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it was the unmeasured disease
and sickness in those studies

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that was triggering
a response in those individuals

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to try and sleep more.

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That's one explanation.

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The second possible explanation
is poor sleep quality,

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because we know that sleep quality,

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independent of sleep quantity,

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is also associated with mortality risk.

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And the lower that your
quality of sleep is,

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the higher your risk of death.

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People who have poor quality of sleep
will typically try to sleep longer;

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they'll try to stay in bed longer
to overcome that poor quality of sleep.

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It may be poor quality of sleep
masquerading as long sleep

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that is associated
with a higher risk of death,

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rather than the long sleep itself.

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But if we take a step back
and think about society overall,

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I think modernity is constantly pushing us

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to, perhaps, work long hours
and therefore neglect our sleep.

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But if we want to be around
long enough to get the benefits

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and the fruits of all of that hard labor,

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we may want to think about starting
to prioritize our sleep some more.