Encouraging Healthy Sleep Patterns: The Impact of Light from Devices

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The Nobel Prize Committee this year awarded its famous prize in Physiology and Medicine to three American scientists: Jeffrey Hall, Michael Rosbash and Michael Young. The trio didn’t even warrant a mention in most Nobel Prize predictions, with breakthroughs in immunotherapies and gene editing stealing the limelight. Most people, myself included, had never given a second thought to the way our bodies physiologically respond to light until Apple released a software update that included ‘Night Shift’, with the following statement: “Studies have shown that exposure to bright blue light in the evening can affect your circadian rhythms and make it harder to fall asleep.”

The Nobel Prize for “[the authors’] discoveries of molecular mechanisms controlling the circadian rhythm” has been welcomed by many within the field, as it comes off the back of decades of rigorous and collaborative research – as most Nobel Prize winning research is.

Children learn that plants react to light by growing plants at primary school, and again at secondary school using phototropism experiments in science class. An important principle of plant biology is that photosynthesising organisms can only photosynthesise during the day; during the night, like us, plants respire. Hall, Rosbash and Young uncovered a complex mechanism by which humans unconsciously and physiologically respond to light – a genetic foundation that regulates our body clocks.

We humans have special light-detecting cells in our eyes called cone cells and rod cells. Rod cells are responsible for night vision; cones activate at higher light levels and are responsible for our perception of colour. What most people don’t know, is that for every one million cone cells, there is one ‘intrinsically photosensitive retinal ganglion’, a newly discovered cell type which contains a light sensitive protein, melanopsin. When light hits these cells in the eye, melanopsin changes shape and triggers a nerve impulse to a special area of the brain (the superchiasmatic nucleus) – the body clock. Brighter, whiter lights, like our phone screens, fluorescent and LED lighting, have a higher proportion of blue (defined by the wavelength of the light), which in turn has higher energy than green, yellow, or red light, in that order. Higher energy blue light is much more effective at activating melanopsin than any other colour, and therefore is more disruptive to our circadian cycles.

Melanopsin activation ‘resets’ our body clocks, and the brain reacts to this by supressing two main hormones: melatonin and leptin. Leptin is responsible for feeling full, and melatonin controls sleepiness. Light exposure in the evening can stimulate hunger, and delay restful sleep by up to three hours. Our bodies don’t have mechanisms to deal with extra caloric intake at night, and sleep deprivation also compounds the growing obesity epidemic. Melatonin is an important anti-oxidant and protects your cells from damage that could lead to ageing and cancer; it’s also good for your immune system, mood and memory.

It’s becoming increasingly harder to naturally achieve a circadian rhythm. You’re more likely than not to sleep with an electronic device by your bed. Furthermore, a 2016 survey mapped global light pollution levels, and found that 60% of Europeans and 80% of North Americans cannot see the Milky Way. People in Singapore are losing their night vision; due to high light levels arising from light pollution, their cone cells are always activated. In London, this is also true – at night we are bathed in a fog of light that mimics an artificial twilight. In other words, if we didn’t draw our curtains, we would never experience true ‘night time’ conditions.

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Figure 1. A: Map of Europe’s light pollution levels with traditional sodium streetlights. B: Forecast of Europe’s light pollution after a transition to more energy efficient white LED streetlights. Key: Blue = 8-16% light pollution (this is where the sky is considered to be polluted by light from an astronomical point of view), yellow and orange = the winter and summer (brighter) Milky Way are obscured, respectively. Red and white areas indicate that the night sky has the same luminosity as the end of nautical twilight. Falchi, F. et al., Sci. Adv., 2016, e1600377.

Evidence suggests that teenagers are twice as susceptible to circadian rhythm disruption by evening light exposure than adults (Touitou, Y. et al., J. Physiol. Paris, 2017). Luckily, as engaged parents, there is a lot you can do to ensure your child’s sleep pattern is healthy:

  • Set bedtimes/a bedtime routine (e.g. shower, mindfulness, bed)
  • Remove technology from your child’s room
  • Filtered light bulbs – you can still have energy-saving LED bulbs, but filter out the high energy blues in the evening
  • Cut down on television in the evening, particularly after supper
  • No caffeine or energy drinks

By Madeleine Iafrate, Pegasus Tutor

Rachel Drew