Tuesday, 15 November 2011

Double Summertime: Double Trouble? - Part 1

This year MP Rebecca Harris has proposed the Daylight Saving Bill. This bill requests a 3 year trial of advancing the clocks by one hour for the entire year. This has been termed “single double summer time”, SDST, and will result in the UK being one hour ahead of GMT during winter, and two in summer. Many social and economic factors have been discussed in the media and Parliament, however the impact on the circadian system, or body clock, has received less attention.

This is quite a large topic, which I’ll deal with in a few blog posts. In this post I will review why light in the morning is important for our body clock. In the second blog post I will review other trials that have tried shifting time zones, and what effect that has had on the population health. Finally, in the third blog post I will respond to the supposed benefits advocated by supporters of SDST.

Light in the morning is the strongest time cue to synchronise our internal body clock with the environment. Our internal clock is responsible for synchronising many bodily functions, including the sleep/wake cycle, metabolism, appetite, digestion, alertness, cognition, athletic performance, blood pressure, body temperature, sex-drive, body repair, energy levels...you get the idea?

Common examples of a desynchronized body clock are seen in shift workers, travellers with jet-lag and sleep disorder sufferers. You will probably even notice this desynchronisation after pulling a few late nighters. A healthy body clock is vital for a healthy body and mind.

Light in the morning provides the strongest cue to sync our body clock with the day (C) jozerC
The influence of light on the human body clock has been widely investigated using bunker isolation units, blind people, and large scale studies. These studies show how our body responds to same amount and type of light differently at different times of the day. 

Bright light in the evening, a result of SDST, delays our body clock. This delay can cause us to need to sleep later, and when we still have to wake up at the same time, can cause ‘social jet-lag’.

Light can also directly affects our hormones, in particular suppressing melatonin production within 20 minutes of light entering our eyes. Melatonin is produced from the brain at night and induces sleepiness. A lack of morning daylight increases the duration of melatonin production, causing sluggishness and inattentiveness.
Key brain regions involved in circadian timekeeping. The brain receives light input from the eye, and uses this signal to co-ordinate time of day information to the rest of the body.

Light at night, which is increased during the summertime with SDST, disrupts our body clock even further. Dr Malcolm von Schantz, an expert in circadian rhythms and sleep research at the University of Surrey, has voiced concerns that light later into the evening can result in poorer sleep quality and less sleep than required. SDST will result in areas in Scotland not having sunset until 11.30pm during summer

It is not sufficient to just count the number of daylight hours, the timing of these hours needs to be considered.


  1. If the intensity of light in the morning and evenings is so important, how do we cope with the massive four hour annual swing in dawn/dusk times that happens naturally, and the accompanying change from 16 hours of daylight to 8? One could speculate that we have some compensating annual rhythm, but isn't it more likely that sleep, eating and electric light are simply more important?

    For most people, when they wake up, go to sleep, work and eat doesn't change at all with the seasons (and therefore lighting). If this is a medical problem that suggests there are much more important societal changes that need to be considered. And if it isn't, obviously that suggests those bodily functions aren't quite as entwined with daylight as you think.

    And a couple more questions: from a circadian health POV,
    1) is BST itself also a mistake?
    2) if you could change the clocks up to once a month, or change our culture and working hours, what would be the optimum system?

    (readers may enjoy http://en.wikipedia.org/wiki/File:Greenwich_GB_DaylightChart.png)

  2. Thanks for your comments and questions A!

    Certainly sleeping, eating, electric lighting, (alarm clocks, exercise...) can all act as cues to align our body clocks with the time of day, however of all the cues, light is physiologically the strongest time cue. If you want to get over jet lag, exposure to morning light will be the quickest and most effective way.

    Without light each morning, we delay our clock, making us want to sleep later in the night. This has knock on effects. As I will show in my next blog post, shifting the clocks by one hour can have noticeable effects in our health.

    I will also talk about SAD, seasonal affective disorder, the seasonal shift to having less light in the Winter can and does have many negative consequences on human health. This occurs when people try and keep the same routines they have the rest of the year, but due to not getting enough light in the morning stop functioning to their full potential.

    There are thought to be 2 million SAD sufferers currently in the UK. Most SAD sufferers find a great amount of relief of symptoms from using light therapy in the morning. (I guess if SDST were to be introduced the companies selling these clocks will benefit from the economy.) http://www.sad.org.uk/

    Is BST also a mistake? BST sets in when we are already get light at 7am, and prevents us having light at 4am in certain months. (I like that graph you linked to, very helpful) Therefore I don't think it has as negative an effect as SDST will have. However, I would love to see more data on the effect BST does have, it certainly can be annoying during the transition weeks.

    To address your last question, having flexible working hours within our society, in my opinion, will be the optimum system. Individuals can be described as larks or owls (or somewhere in the middle, like myself) and this can also change with age. In an ideal world we would be able to work at the time of day when we were most concentrated and able, however, I realise this isn't going to be possible in many jobs (e.g. shiftworkers). What we should do is to know about how light effects people, and use it to optimise their clock to their schedule, e.g. using daylight lamps in the morning, having red tinted monitors for computer work in the evening, not having SDST :P