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.