Clocking on to Sleep

Posted by es328 at Mar 23, 2017 10:57 AM |
Ahead of the change to British Summer Time on Sunday 26 March, Professor Jim Horne explains the effect of daylight savings on sleep and the brain

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We humans are particularly poor at seeing in the dark, and before the advent of artificial lighting, sleep kept us out of harm’s way, especially during the long winter nights.  Yet, it was unwise to slumber on after sunrise, when predators and were up and about, which is why daylight tends to wake us up, and is why seasonal differences in daylight, weather and other factors would, in those days, lead to changes in nightly sleep [1]. Even today, native peoples living without electric light in Africa sleep around 1½ hour longer in their Winter compared with their Summer [2], seemingly without changes to daytime sleepiness. However, in the UK, despite the roughly eight hour seasonal difference in daylight, there is little by way of seasonal change to our sleep, with the average nightly sleep duration for healthy adults being about 7 hours, and has remained unchanged at least over the last 50 years [3].

Worries that the clocks going forward causes sleep loss may lead to more accidents, goes back well over a hundred years, and was one of many arguments used against the intended introduction of daylight saving time (DST), first proposed in the UK by the enthusiastic William Willett to “improve health and happiness”.  He was a wealthy builder who, in 1907, and at his own expense, produced the pamphlet, “Waste of Daylight”, distributed widely, including MPs, town councils and businesses.  In it he wrote, “That so many as 210 hours of daylight are to all intents and purposes wasted every year, is a defect in our civilisation. Let England recognise and remedy it. Let us not be so faint-hearted as to hesitate to make the effort when the cost is to trifling and the reward so great”. Inspiring stuff, and this is just a sample.

Mindful of sudden changes, he suggested adding 20 minutes to clocks each Sunday night for four consecutive weeks in the spring, accumulating to 80 minutes of daylight saving per day, and then to reverse this in the autumn.  He even provided a detailed cost-benefit analysis, calculating that DST would save precisely £2,546,834 annually, for the whole nation. Nevertheless, it was ridiculed at first, despite the support of the young MP, Winston Churchill, and Sir Arthur Conan Doyle. Unfortunately Willett never lived to see DST becoming law, as he died of influenza in 1915.  Ironically, the next year it was introduced as an emergency wartime measure, throughout Europe (even in Germany where it had been introduced on orders of the Kaiser Wilhelm), but was then dropped after the war, only to be gradually reintroduced.  Sadly, Willett’s efforts are mostly forgotten, except in his home town of Pitts Wood, Kent, where there is a memorial sundial set permanently to DST, and a pub, The Daylight Inn.

In 1968 the UK changed to continuous British Standard Time (BST), mostly for commercial reasons.  But due to public pressure, mostly from those living in the north, the Government abandoned it in 1972, reverting back to DST, and to rename BST as British Summer Time, versus Greenwich Mean Time (GMT) for the winter. For a day or two after switching to DST in the Spring, there are more accidents probably with sleep loss being a factor, whereas following the return to GMT with a one-hour sleep gain, there is no such effect [4].

The powerful influence of daylight, even bright indoor light, not only can shift the body (circadian) clock, but has a much more rapid, albeit temporary, alerting effect on the brain [5], which is a useful ‘quick-fix’ to suppress that early morning ‘trough’ experienced by night-workers – more so if the light has a slight blue tinge.  Moreover, bright light reduce that afternoon ‘dip’ in alertness, which, by the way, is a very useful trick for reducing daytime sleep in babies as this leads to better nighttime sleep and helps train their circadian clock– let them have their daytime naps in the light, not in that darkened room.

1 Ekart 2005 At day’s close – Weidenfeld & Nicholson

2 Yetish et al 2015 Current Biology 25: 2062-8

3.Horne JA 2016 Sleeplessness - Palgrave McMillan

4. Barnes CM & Wagner DT 2009 J Appl Psychol 94: 1305-17

5. Cajochen C 2007 Sleep Med Rev  11: 453-64

By Professor Jim Horne, Department of Neuroscience, Psychology and Behaviour, University of Leicester

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