Sleep – when is enough, enough?

Posted by ap507 at Mar 13, 2018 04:53 PM |
In preparation for World Sleep Day (16 March), Professor Jim Horne answers the important question: are we really getting enough sleep?

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Seemingly, too many of us suffer from ‘sleep debt’, in failing to get that all too often advocated eight or so hours a night; lack of which is seen to lead to obesity, diabetes and related disorders.  Findings of ‘diabetic like’ states appearing when otherwise healthy people have their sleep restricted to four hours for several nights, might well back this up.

Maybe even eight hours is not enough, as there are claims that earlier generations averaged 9 hours sleep a night and that, today, we rely too heavily on alarm clocks, live in an overworked society, spend late nights using electronic paraphernalia, and that sleeping longer at weekends is indicative of trying to repay the previous week’s sleep debt.

Indeed, surveys asking people if they would like more sleep, report many saying ‘yes’, and studies using very sensitive tests of sleepiness find apparently high levels among the general population.

All of which is particularly worrying for those with insomnia, whom struggle for even six hours of sleep, and whose anxieties are aggravated by the thought of striving for even more sleep so as to offset those apparent ill-health effects.  Needless to say, the demand for sleep aids is booming. 

Plus ça change as, for example, in 1894 the British Medical Journal lamented  that, ‘The hurry and excitement of modern life is held to be responsible for much of the insomnia of which we hear; and most of the articles and letters are full of good advice to live more quietly and of platitudes concerning the harmfulness of rush and worry. The pity of it is that so many people are unable to follow this good advice and are obliged to lead a life of anxiety and high tension.’

However, today, most of us have quite adequate sleep, and the belief that we all need 8 hours overlooks natural individual differences in sleep. Evidence that not so long ago we slept for even longer largely stems from misinterpretations of a 100 year old study - not on adults, but from teenagers, who indeed slept around 9 hours, and  still do today !  In fact, several findings over the last 50 years show that our 7 hour average sleep has changed little in the UK.  Elsewhere, for example, in Scandinavia, it has fallen only by 20 minutes, and in the USA the proportion of adults sleeping fewer than 6 hours has increased by less than 2%.

We can also sleep for pleasure, of course, beyond necessity, as in ‘lie-ins’, which are not necessarily a sign of catching up on sleep debt.  Similarly, we eat and drink in excess of need, simply for enjoyment, Moreover, when we are asked that leading question, “would you like more sleep?, it invites a positive response, as does, “would you like more pay, ‘longer holidays’ etc.?  But how many of us would forego the time and effort to achieve those ends, rather than simply acquiesce with ‘yes’?

Few obese adults are short sleepers, few short-sleeping adults are obese, and insomnia doesn’t lead to obesity - usually the opposite. Claims that sleep debt actually causes obesity, diabetes, even heart disease are overstated, being largely based on correlations, where these effects, including the sleep debt itself, are more likely due to common, deeper underlying causes. Laboratory studies pointing to short sleep leading to diabetes-like symptoms typically require restricting sleep to 4 hours a day, which is extreme, stressful and leads to overwhelming sleepiness.  Even in people who habitually sleep only 5 hours, any weight gain which could actually be caused by sleep debt, is typically less than 2 kg a year.  Maybe worrying year on year, but there’s little support for this gain being prevented by simply extending sleep an hour or two, or by using sleeping tablets. Instead, far more effective, here, would be to spend just 20 minutes of that presumed two hours in daily brisk walking (and in contemplating a better diet).

Besides, judging our sleep merely by its length is a crude index, and overlooks sleep quality and the continuity of its component ‘stages’ during the course of sleep, which are equally important.  The acid test of inadequate sleep is daytime sleepiness throughout most of the day, and assertions that healthy adults without this may, unknowingly, have chronic sleepiness, are largely based on very sensitive, arguably oversensitive laboratory tests. Feeling ‘tired all the time’, often suggestive of sleep debt, is not always what it seems and can be the cause of poor sleep, not vice versa, and unlikely to be rectified by extra sleep.


More about this in:

Jim Horne ‘Sleeplessness – assessing sleep need in society today’ – Palgrave McMillan 

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