Circadian Rhythms

In Our Time: Series 18, Episode 12


Proctor and Gamble had organised the factory on rotating shifts.  One week she left the house at 5.30am and got home at 2.30pm, the next week she left at 1.30pm and was home at 10.30pm, and the third she left home at 9.30pm and returned at 6.30am.

The Working Poor

When I went and talked to my aunt about my father’s family she told me a lot of great stories.  One of them was about my paternal grandfather who was born in 1890s. When he was entering old age he lived in a house with two of his grown up daughters who eventually saved enough money between them to get their house attached to electricity.  He wasn’t a fan of the idea, but grouchily acquiesced.  One thing he wouldn’t do though was use it himself.  Turning on electric lights might be all well and good for his daughters, but when he took himself off to bed he went with a candle.  None of this new-fangled crap for him.

Which is an amusing story that also illuminates (sorry) a huge shift in the way human beings have extended their daylight in the last century, especially since electrification became domestic.  Before gas lighting, lamps and then electrification there were pretty limited things you could do with your time after dark other than sleep.  One version of this story is that expanding “daylight” is good and a symbol of progress and civilisation.  Another version concerns biology.  The biological story of extending days, artificial light and shift work  is not so positive.

I am not used to thinking of myself as a servant to my biology; for most of us (or maybe it’s just me) there is something a bit off-putting about it.  Science suggests less and less is really under our control and free will seems something set within very narrow parameters.  Once you’ve taken biology, culture and your own position within a society into account it can feel like free will boils down to the trivial decisions: shall I watch TV or listen to music?

This podcast was about circadian rhythms and like most things to do with science most of this was news to me.  Outside of knowing what a circadian rhythm was, I hadn’t given it much thought.  Of course it makes sense that feeling tired and feeling the increasing need to sleep (sleep pressure) is part of biology’s way of running our bodies efficiently.  It is surprising to realise that just as the little daisies in the lawn that close their petals at night and open in the morning so are we controlled by light.

A small area of the hypothalamus in our brain holds our internal clock, which is set by natural light.  Our clock gathers its information about natural light from our eye which – so scientists only recently discovered – has a set of special cells within it that detect brightness.  This 24 hour clock tells us when to sleep and when to be awake, and a whole suite of biological responses are built around this.

A set of commonly observable phenomenon come from our circadian clocks.  For example, morning people and evening people (circadian clocks vary in humans by up to an hour, some are set early and some late), sleepy teenagers in the morning (circadian clocks change with human development), and jet lag (shifting our internal clocks in space does not shift them in time, for a while).

I can see why this is an expanding area of study because it touches so many things.  Each time this week’s guests spoke it sounded like another potential research project.  Some of the research they have already done is incredibly illuminating.  For example, discovering that the eye has special brightness receptors that set the circadian clock led them to wonder what happened for blind people.  It turns out that completely blind people struggle with this; that they are often fighting the slow drift of their circadian clock against their social clock.  Drugs connected with melatonin can help.

Then there are all the possible areas of research to do with working in conditions of artificial light.  We are becoming less and less entrained to natural light.  This also connects to shift workers.  People don’t just “adjust” because the internal clock obeys sunlight not artificial light.  To actually adjust you need to hide from natural light.  Achieving this adjustment to artificial light however seems a Pyrrhic victory and is associated with (but not directly linked) with many negative health impacts both physical and mental.

And then there is sleep.  Why sleep?  Aside from giving us the opportunity to stop checking our work emails it is a time when the brain reorganises itself; when it consolidates memory.  Strikingly, sleep also connects to mental health, for every mental illness is associated with a sleep disorder, and – it transpires – the sleep and mental health pathways in the brain overlap.  Which is science showing us something we already knew.  We already know that stress, upset and anger makes it hard to sleep.  If we think of mental health as being a continuum, then those periods of emotional upset push us along the line towards poor mental health and our sleep is impacted.

Then, I suppose, we go to research about how to fix these problems in people who are always down the poor mental health end of the continuum.  Which is where I come up against a recurring issue I have with health issues.  I also listen to On Being, which is routinely good but sometimes frustrating.  For example, on episode had a person talking about suicide.  It was interesting, and stressed the importance of making people aware of why they shouldn’t.  Along the way we learned all the statistics about rising rates of suicide among certain groups (more US soldiers dying of suicide than combat, was a striking statistic).  Lacking though was any thought about why this is all happening.  We’re always fixing the symptoms of our society and not addressing the causes of our illness.

And so, back to the subject of sleep and mental health, it feels a lot like the idea that we have 8 hours to work, 8 hours to pursue recreation, and 8 hours to sleep is a good one, and that looking at ways to adjust people to shift work, and find drugs to combat severe depression, and interventions to combat obesity may not be the best solution in the long-term.  I understand the need to help people in the moment, but the wider picture never seems to be addressed.

One of my upcoming new year’s resolution though is to not get bent out of shape about the wider picture and look to myself and my family.  In light of that, I conclude that sleeping is important and that staying up late all the time is bad for me.  Funny that.

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I wrote a book called Kaitiaki o te Pō

2 thoughts on “Circadian Rhythms”

  1. Yeah, I’ve twice done camping in the backyard and found it hard going. It gets bloody cold for one, and Eleanor kept waking up and coughing. I think you would adjust eventually, but we’re not really set to daylight anymore I suppose. Still, I reckon I’ll give it a go again this summer.

  2. Did the camping thing in the backyard with a make-shift tent and two small children. The twilight lasted for an age given the time of year and the stars took their time at being a little heavenly wonder. The day also came early with birdsong and cool condensed air on fabric. If you don’t get your 6-8 hours of sleep – life seems harder.

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