1
00:00:00,128 --> 00:00:01,656
So far, we've spoken about

2
00:00:01,680 --> 00:00:05,536
all of the wonderful
benefits that sleep provides,

3
00:00:05,560 --> 00:00:09,040
but how much sleep should
we actually be getting?

4
00:00:09,064 --> 00:00:11,842
[Sleeping with Science]

5
00:00:11,866 --> 00:00:13,892
(Music)

6
00:00:13,916 --> 00:00:16,936
For the average adult,
the current recommendation

7
00:00:16,960 --> 00:00:20,726
is somewhere between seven to nine
hours of sleep a night.

8
00:00:20,750 --> 00:00:24,626
And what we've been finding
from large-scale epidemiological studies

9
00:00:24,650 --> 00:00:28,446
is that, using that reference point
of seven to nine hours,

10
00:00:28,470 --> 00:00:30,456
once you start to drop below that,

11
00:00:30,480 --> 00:00:34,146
your mortality risk
actually starts to increase.

12
00:00:34,170 --> 00:00:39,696
In fact, the Center for Disease Control
in the United States, or the CDC,

13
00:00:39,720 --> 00:00:43,276
they stipulate a minimum
of seven hours of sleep a night

14
00:00:43,300 --> 00:00:44,486
for the average adult.

15
00:00:44,510 --> 00:00:47,226
In other words, the shorter your sleep,

16
00:00:47,250 --> 00:00:48,726
the shorter your life.

17
00:00:48,750 --> 00:00:54,806
But it turns out that it's not quite
a linear relationship as you would expect.

18
00:00:54,830 --> 00:00:57,956
It's not as though the more
and more that you sleep,

19
00:00:57,980 --> 00:01:01,246
the lower and lower
your mortality risk is.

20
00:01:01,270 --> 00:01:03,786
In fact, something strange happens.

21
00:01:03,810 --> 00:01:06,386
Once you get past nine hours,

22
00:01:06,410 --> 00:01:11,116
you actually start to see
a rise back up in mortality risk,

23
00:01:11,140 --> 00:01:13,336
which seems rather strange and peculiar.

24
00:01:13,360 --> 00:01:18,836
And scientists have actually put forward
at least two different explanations.

25
00:01:18,860 --> 00:01:22,626
The first is that,
if you look at those studies,

26
00:01:22,650 --> 00:01:28,896
it may be that individuals are suffering
from significant disease and illness.

27
00:01:28,920 --> 00:01:32,076
When we become infected,
or we have disease,

28
00:01:32,100 --> 00:01:35,776
typically, we try to sleep longer,
we stay in bed longer.

29
00:01:35,800 --> 00:01:36,958
So in other words,

30
00:01:36,982 --> 00:01:41,501
it was the unmeasured disease
and sickness in those studies

31
00:01:41,525 --> 00:01:45,231
that was triggering
a response in those individuals

32
00:01:45,255 --> 00:01:46,791
to try and sleep more.

33
00:01:46,815 --> 00:01:48,081
That's one explanation.

34
00:01:48,105 --> 00:01:52,201
The second possible explanation
is poor sleep quality,

35
00:01:52,225 --> 00:01:54,881
because we know that sleep quality,

36
00:01:54,905 --> 00:01:58,301
independent of sleep quantity,

37
00:01:58,325 --> 00:02:01,831
is also associated with mortality risk.

38
00:02:01,855 --> 00:02:04,940
And the lower that your
quality of sleep is,

39
00:02:04,964 --> 00:02:06,971
the higher your risk of death.

40
00:02:06,995 --> 00:02:11,751
People who have poor quality of sleep
will typically try to sleep longer;

41
00:02:11,775 --> 00:02:17,021
they'll try to stay in bed longer
to overcome that poor quality of sleep.

42
00:02:17,045 --> 00:02:22,531
It may be poor quality of sleep
masquerading as long sleep

43
00:02:22,555 --> 00:02:25,671
that is associated
with a higher risk of death,

44
00:02:25,695 --> 00:02:28,221
rather than the long sleep itself.

45
00:02:28,245 --> 00:02:33,341
But if we take a step back
and think about society overall,

46
00:02:33,365 --> 00:02:36,841
I think modernity is constantly pushing us

47
00:02:36,865 --> 00:02:42,111
to, perhaps, work long hours
and therefore neglect our sleep.

48
00:02:42,135 --> 00:02:46,381
But if we want to be around
long enough to get the benefits

49
00:02:46,405 --> 00:02:49,611
and the fruits of all of that hard labor,

50
00:02:49,635 --> 00:02:53,638
we may want to think about starting
to prioritize our sleep some more.