Question:
"Sleeping for more than 8 hours a night was associated with increased
mortality, but it mattered little whether sleep was taken in the early or
late part of the night"
In fact they say this several times. Is this an accepted fact or just
something that "seems true" for some reason?
Answer:
It should be noted that Franklin's adage was coined at a time when there were
no electric lights (or computers), and were therefore much more controlled by
the presence or absence of the sun.
It is also possible that he intended the adage to apply to people under the
age of 65.
Well I doubt that Franklin said this based on any sort of stringent
scientific study either. But the studies findings that mortality was linked
to over sleeping caught me by surprise.
Fact. But there are tons of associations like this that don't
mean much causally. Lots of things cause excessive sleep (or time
in bed). Some of them cause health problems.
Self-reported habitual sleep time is an important variable because short
and long sleep times are associated with mortality.
Speculation with regard to these results usually focuses on physical
health, rather than psychological factors. We investigated
the role of anxiety and depression in reports of habitual sleep times by
examining the relative and absolute discrepancy
between individuals' initial estimates of their sleep times and sleep
diaries made over a 2-week period. Results indicated that
depressed mood was associated not only with a tendency initially to
underestimate length of sleep (relative discrepancy), but
also to exaggerate reported sleep time regardless of direction (absolute
discrepancy). These results imply that studies that
examine relationships between reported sleep times and mortality should
take mental health factors into account.
It has also been reported that much shorter than 8 hours sleep can be
unhealthy, but here is another viewpoint.
