Two-minute explainer: Circadian rhythms

Circadian rhythms describe patterns of behaviour that exist in most things that live on this planet of ours. It’s not just the higher mammals that exhibit these patterns, you’ll find it in most organisms, from plants and animals all the way down to microbes. However, we are the only species that makes a habit of living in ways that disturb our natural balance with the world around us.

Circadian comes from the Latin ‘circa, meaning’ ‘about’ and ‘dies’ meaning ‘day’. So, a circadian rhythm is a repeating pattern based on the natural progression of night and day. The study of circadian rhythms is chronobiology; this time from the Greek ‘chronos’, meaning ‘time’, ‘bio’ meaning ‘life’ and ‘logos’ meaning ‘discourse’ or ‘thought’. What it must be to have had a classical education.

As we’re all aware, the obvious example of a circadian rhythm is our decision to sleep when it's dark and to do stuff during the day. On one level it’s just the practical thing to do, given that most of us require illumination to function, so darkness serves us well as the time to rest. But there’s a chemical response going on as well.

During the day, the eye gathers light information, most of which we translate into images of the external world, but the eye also gathers information about light values, in particular the amount of blue light that is present in the environment. Most of us know about the rods and cones that govern the visible side of things, but recently another cell has been found within the retina. These are called, unpromisingly, the Intrinsically Photosensitive Retinal Ganglion Cells (or ipRGC). They are sensitive to a narrow range of blue light, around 480nm, and it's these cells that control the ability of the body to go to sleep.

Tucked safely away within the centre of our brains is the pineal gland. This was once known as the ‘third eye’ and it tells us when it’s time to go to bed. Once the amount of 480nm blue drops below a certain level, the pineal gland starts to secrete a hormone called melatonin. It doesn’t start with a rush, because then we might fall over in the street. Rather, as the amount of 480nm blue begins to fall away, the pineal gland releases corresponding levels of melatonin into our systems.

The highest levels of melatonin are produced between midnight and 8.00am, and therein lies a problem for the complex societies that most human beings have chosen to inhabit. While most of us hope to enjoy a regular night of uninterrupted sleep, there are those whose role it is to maintain the social fabric while we take our rest. Shift work has long been an issue for health professionals. Studies have connected shiftwork with cancers, heart disease and diabetes. Other findings have also indicated a connection with digestive disorders and menstruation irregularities. So a disturbed circadian rhythm is not a good thing, but its hardly imaginable that a highly technologized society can exist without a standing army of people working through the night.

Don't try this at home.

We can also be our own worst enemies without the benefit of an anti-social working pattern. Our addiction to social media and hand-held devices (and I’m going to include BOOKS in that category) can all help to interfere with our circadian rhythms. It used to be felt, up to a few months ago, that the amount of blue light in computer screens, TV screens and mobiles and tablets could interfere with melatonin production. More recent research is suggesting that there is insufficient 480n blue light in these screens, but the sleep disturbance pattern is still being exhibited. I’d suggest that we’re over-stimulating our brains at a time when we should be turning away from external influences and getting ready for a good night’s sleep. So forget anything after News at Ten – and don’t watch News at Ten either because it’s too depressing.

Air travellers experience another kind of circadian disruption in the form of jet lag. The body is trying to hold onto a diurnal pattern, but disruption is caused as a consequence of the changes in external stimuli due to long-distance trans-meridian travel (east-west and west-east). Obviously, the more trans-meridian travel that takes place in a given period, the more confused the body can become.

 Can anything be done to correct the damage being done by our own behaviour?

It used to be thought that shiftworkers should be bathed in blue-saturated light to prevent melatonin being produced in the first place. This proved to be a catastrophically bad thing to do as it effectively created a jet lag effect on top of the disrupted sleep pattern. The only thing left for the shiftworker to do was to go home and collapse into their beds until the next shift was due to begin. This is considered to be an unsociable, if not cruel, thing to expect.

Current thinking is that the melatonin should be allowed into the system, so ensuring that the 480n blue light is sufficiently diminished, and then to create an illuminated environment where illuminance levels are generally higher, to help with the necessary concentration on the tasks being undertaken. The body received its dose of melatonin, but the mind and body continue to function. And at the moment, that’s the best advice that’s on offer.


As regards curing jet lag, this is more like everyone’s favourite hangover cure.

Here are a few of the ideas:

  1. Stock up on sleep so you don’t feel so wasted, though this sounds like a sleepless night to me. And drink lots of water.
  2. Don’t try to hold onto previous sleep patterns and go immediately into the diurnal pattern of the place to which you are heading. This may mean going almost a whole day without sleep, of course. And drink lots of water.
  3. Alcohol and caffeine are not a good idea. And drink lots of water.
  4. Depending on your direction of travel, get ahead of your sleeping time by adjusting earlier in the day. And drink lots of water.
  5. Think about your stomach and listen to what it tells you about sleeping and eating. A full dinner may not be a good idea, but a cup of herbal tea (or water) might be just the ticket.
  6. Human-centric lighting will be explored in the Workplace and Wellbeing Conference at LuxLive 2018, Europe's largest annual lighting event taking place on 14th & 15th November at the ExCeL London. Featuring eight conference tracks and over 100 expert industry speakers. Entry is FREE – simply register to attend HERE 
    Be clever with light. Travel with sunglasses to reduce light into the eye at inappropriate times during journeys. This may involve drinking water.


There’s also a suggestion that the circadian rhythm can be accelerated by very high illuminance levels in short bursts. This suggests that the body is being re-set from a daytime standpoint. If you’re adjusting into a night-time pattern there’s the option of ingesting small amounts of commercially-available melatonin, a remedy that’s supported by the medical profession. Persionally, the less weird stuff that I put into my body the better I like it, but it's an option.

Main image: The Midnight Sun, Anda Berczky, 2005. Man with smart phone:


  • Human-centric lighting will be explored in the Workplace and Wellbeing Conference at LuxLive 2018, Europe's largest annual lighting event taking place on 14th & 15th November at the ExCeL London. Featuring eight conference tracks and over 100 expert industry speakers. Entry is FREE – simply register to attend HERE