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Changes over a
lifetime (more detail)
Infancy
The
infant child sleeps much longer than an adult. In the first year of
life a child will typically spend about 16 hours asleep, half of this
being in REM. By the age of one this has dropped to about 12 hours of
total sleep with about four hours of REM. Lots of sleep in early life
does seem to tie in with restoration theory, since this is a time of
rapid growth both in the body and in the brain. Early life is a steep
learning curve so presumably the brain is working over time to
assimilate all this new information by making new and ever more complex
interconnections. According to Oswald this would be facilitated by
plenty of REM sleep.
Evolutionary sleep theorists suggest all this infant sleep is designed
to take the pressure off of parents who can get on with essential chores
such as finding food.
Adolescence
By
adolescence hormones seem to be playing an ever-increasing role in the
sleep pattern. Hormone production at night is disturbing sleep and
leading to sleep deprivation. Studies suggest that adolescents need
more sleep that pre-adolescents not less. However, schools usually
expect the older age group to start earlier than the younger age group.
Recent research is suggesting that many adolescents have DSPS (mentioned
in biorhythms) that results in later sleep onset and difficulty waking
in the morning. As a result some schools are now experimenting with a
later start to the school day and are reporting improved performance and
results.
Adulthood
By
the time we have reached maturity we usually sleep for 8 hours with only
one quarter (2 hours) being spent in REM. Note, people who sleep longer
tend to spend much of the extra time in REM. As a species, in the West
we sleep less than we did a century ago. It is estimated that in the UK
we now spend only 7.5 hours asleep per night compared with 9 hours in
Victorian times.
Kripke et al (2002) report that sleeping longer is correlated with
ill-health. In a huge survey of over one million adults they found that
those sleeping six or seven hours have a greater life expectancy than
those sleeping eight hours longer. However, you have probably noticed
the weak link in this argument… the word ‘correlated!’ It would seem
likely that people who are ill may need to sleep longer, so underlying
health problems are causing the increase in mortality and the increased
need for sleep.
The wrinkly years
As
we get older still there are further changes. REM continues to
decrease, and by the time we reach 60, stage 4 is non-existent. As a
result older people are more easily awoken and often complain of
insomnia. This loss of deep sleep may explain the deterioration seen in
later life. No deep sleep, no growth hormone for repairs. As a result
there is increased loss of muscle tone, lack of energy and increased
risk of osteoporosis as bone density declines.
Co-sleep
Most older people sleep with a partner. Relatively little research has
been carried out into the affect this has on sleep patterns.
Kloesch et al (2006) found that the male sleep pattern seems to be most
disrupted, to the extent where cognitive functioning is impaired.
Eight unmarried, childless couples in their twenties were asked to spend
ten nights sleeping together and ten nights sleeping apart. They were
given questionnaires and asked to complete a variety of tasks the next
day.
The
men reported sleeping better with a partner despite their sleep
appearing to be more disturbed. Co-sleeping also raised the levels of
men’s stress hormones. Women on the other hand were found to sleep more
deeply.
Dr
Stanley believes that we are not designed to sleep together. Few other
species do, but modern human society sees it as the norm. He describes
it as ‘bizarre thing to do.’
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Research into age lifespan changes
Van
Cauter et al (2000) carried out a longitudinal sleep study on 149 male
participants (aged 16 to 83) over a 14 year period (though I’m not sure
how many of the 83 year olds would have seen the study through to the
end!).
Of
particular interest was their finding that deep sleep and as a result
production of growth hormone, deteriorates in two stages:
-
Between 16 and 35 years and then again
-
Between 35 and 50 years
Meaning that between these years the amount of repair to body tissues is
reduced. In fact by the age of 45 there is so little growth and repair
that muscle tone begin to fade, exercise becomes more difficult and
obesity is more likely.
The
researchers considered this from an evolutionary perspective.
In
our ancient past when we were still hunter-gatherers, our life
expectancy would have been less than half of what it is in the Western
World today. Certainly 30 would have been getting on a bit and it’s
unlikely that many would have ever reached 45. As a result, with death
so imminent what would have been the point of producing growth hormone
and carrying out repairs to a decrepit body? No growth hormone needed…
no deep sleep needed.
These findings are supported by other studies that suggest as we get
older there are
-
decreases in
total sleep time, deep sleep time and REM sleep time
-
increases in
sleep latency (time taken to nod off) and stages 1 and 2 sleep time.
Dozing and depression in the elderly
In
older people there may also be a link between dozing and depression.
Foley et al (2000) carried out a telephone poll and questioned people on
their sleeping habits and mood. A significant correlation was found.
However, telephone polls are a notoriously poor way of obtaining a
sample since people are even less likely to be honest on the phone than
they are face to face.
Also being a correlation I’m sure you can also tell me we can’t prove a
cause and effect relationship. The assumption is that the depression
results from the dozing but it is just as likely that being depressed is
leading to dozing or even more likely that a third event such as
bereavement or lack of job is causing both.
However, in support of the theory it has been suggested that older women
who report sleeping well suffer fewer problems with mood, memory and
issues of attention and are less likely to suffer from physical
disorders such as diabetes and CHD. (Aneoli-Israel 2008)
Evaluation points to make on lifespan changes
The
measures used for testing age differences are scientifically rigorous,
use objective measures of sleep such as EEG, EMG and levels of
breathing. As such they are replicable and appear to be reliable.
However most information is gathered in sleep labs which are very
artificial and may affect sleep patterns. Participants are wired to
electrodes over large parts of their head, face and body. They have
straps to measure their breathing and sometimes even penile erections
(not so widely used in women). They are aware of being watched and
expected to sleep in unfamiliar beds. Research therefore lacks mundane
realism so it is difficult to generalise the findings to real life!
That is ecological validity is low.
Self report methods used in dream research is subjective and may be open
to researcher bias.
There is a big
question mark over whether or not older people really do sleep so much
less than younger adults. There certainly appears to be less nocturnal
sleep, however, some or all of tis could be made up by afternoon naps.
Borberley et al (1981) reported that 60% of 65 to 80 year olds regularly
take naps in the afternoon.
There is also a big
discrepancy in research into the different age groups. In the past
twenty years or so there has been a focus on infant sleep patterns and
habits, largely due to research into sudden infant death syndrome (what
the tabloids call ‘cot death). In contrast to this relatively little
research has been carried out on the middle aged. Dement attributes
this lack of information to practical reasons; namely the constraints on
this age group such as pressures of work and families etc. They simply
don’t have the time to spend in sleep labs for weeks on end as the other
age groups do.
Despite their being
obvious average differences in the amount we sleep at different ages,
research also points to there being huge individual age differences
within each grouping. So within my age group there will be those
managing perfectly well on four hours of sleep whilst others will be
suffering tiredness despite eight or nine hours. It seems that
individual differences are every bit as important as age differences
when studying sleep.
Cultural differences
In Northern and
Central Europe, North America sleep is usually monophasic (one long
period of nocturnal sleep, typically lasting 7 or 8 hours). Text books
seem to consider this to be the norm; yet another example of
ethnocentricism, imposed etic and ‘West is Best’ attitude.
Those travelling to
southern Europe or South America may have noticed a different and more
practical sleep pattern in these sunnier climes. The afternoon siesta,
often lasting two or three hours followed by a much later nocturnal
sleep is considered the norm and appears to produce no additional
deficits to monophasic sleep.
Hope you found this interesting. I
quite enjoyed writing this section on age differences in sleep. As I
said you could incorporate this information into a question on sleep
research or a question on biorhythms. Even if you have no opportunity
to use it, I’m sure that you could bore friends with it endlessly at
parties or adapt it as a source of chat up line
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