Professor Jim Horne

Sleep Neuroscientist − BSc, MSc, PhD, DSc, FSB, FBPsS, CPsych, CBiol





Loughborough Sleep Research Centre

Awake Ltd

Journal of Sleep Research

Jim Horne at

Jim Horne at Google Scholar





The general impression is that ‘healthy sleep’ should comprise eight hours of uninterrupted slumber at night, following a fairly rapid sleep onset, and that daytime napping is more for wimps.  But all this is largely a modern convention as none of it really reflects what ‘nature intended’, or what life was really like.  Most of us don’t actually obtain this magical eight hours, as over the last 50 years or so, the average daily sleep for healthy adults has always been just over seven hours, with most people claiming to cope quite well on this amount.  Even so, we can easily extend our night’s sleep by an hour or so, and on a permanent basis if only given the opportunity to do so.  However, in a recent sleep survey in almost 11,000 adults, we found that most of those who said they would like more sleep, would not actually take it if offered an imaginary free hour in the day, and when there were other attractive waking alternatives.  Seemingly, most adults would enjoy more sleep but are not prepared to forfeit other waking needs and pleasures.  Surprisingly, there was no link between wanting more sleep and the extent of daytime sleepiness, as one would have expected that the greater this desire for sleep, the worse would have been the sleepiness.


The most noticeable effect of having an extra hour’s sleep at night is for any afternoon ‘dip’ to disappear.  But there are drawbacks in sleeping to excess, night after night, as this reduces sleep ‘pressure’ at bed-time, causing a longer time to fall asleep, followed by less intense and fitful sleep in the small hours.  For those concerned about their dip, then rather than take more sleep at night, pre-empt the dip with an afternoon nap – not too long, as this leads to grogginess, but not too short.  Four minutes is the minimum, and about 15 minutes is ideal (maybe taken during a tea break).  This being just as effective as an hour’s extra sleep in the morning, and with the seven hours at night, there’s no need for that eight hours at night, anyway.


Whereas only about a fifth of our survey regularly took afternoon naps, maybe as most didn’t want to be caught napping, the dip is found in all peoples throughout the world, especially in hot climates, where it is more than just ’40 winks’, to become the much longer siesta.  Well and truly part of the daily sleep quota, siestas avoid the afternoon heat, leaving only around five hours sleep needed at night, and with the added benefit of a much later bed-time and the enjoyment of a longer, cooler evening.


Several hundred years ago, dividing up daily sleep up in a similar way was commonplace in the UK, when people would have a ‘fyrste sleepe’ of around two hours, taken not so much in the afternoon, but early evening, followed by supper and the greater opportunity for more lively interactions with family and friends.  Bed-time would be around midnight, followed by a few hours of sleep before being interrupted with prayers, or the need to kindle the fire and ensure that home and family were safe.  The final return to sleep would be until dawn, making around seven hours daily sleep in total.  In those days, sleeplessness at night was seen to be more ‘normal’, and not the problem it is in today’s ever-busy 24/7 society, and when until very recently the taking of ‘40 winks was indeed for wimps.  But simply re-branding it as a ‘power nap’ was a master stroke, to give it that macho image.


Why ‘40 winks’ rather than, say 30 or 50 winks ?  No one really knows, but one answer seems to be that forty is a lucky number, mentioned in various religious texts (eg ‘forty days and forty nights).  Or, one could argue from a more ‘scientific’ basis that if a ‘wink’ is that short period of ‘droopy eyes (a ‘microsleep’), lasting about 6 seconds, when we are struggling to remain awake, then co-incidentally or otherwise, forty add up to that critical four minute minimum for that worthwhile power nap.