I’m someone who often has trouble sleeping so when I came across Lynne Peeples’ book, The Inner Clock: Living in Sync with Our Circadian Rhythms, I decided to read it in the hope of getting some tips and advice. It turned out to be more of a science book than a self-help book, but I found it absolutely fascinating.

Lynne Peeples is a writer and journalist based in Seattle and goes to impressive lengths in order to carry out her research for this book. In the first chapter, she describes how she spent ten days in an underground bunker in Arkansas with no access to clocks or any natural light at all as part of an experiment to see if she could guess the time of day based only on her own body’s circadian rhythms. The circadian clock is the part of the brain that controls our sleep-wake cycle, hunger, metabolism, hormone production and other important functions; we also have other local clocks in almost every organ and tissue of the body and sometimes these clocks can get out of sync with each other which causes all sorts of problems. Peeples’ experiment helps her to understand the natural patterns of her own clocks and how they can be affected by light, food and drink, activity and other factors. This forms the basis of the rest of the book.

Peeples gives most attention to the effects of light, both natural and artificial – not just the amount of light we’re exposed to, but the type and quality of the light. The ‘bad’ kind of light, as we all know, is the blue light from phones and laptops, which is one of the reasons we’re told to limit their use before bedtime. However, we can counteract the effects of screens and artificial lights later in the day by making sure we get plenty of natural light throughout the day. Working in an office with windows is good for your circadian clock, but Peeples suggests that your distance from the window and even the angle of your desk can also make a big difference. Of course, sometimes a lack of daylight or exposure to too much artificial light is out of our control and there’s an interesting section where she discusses the inequalities experienced by people living in urban areas compared to rural ones.

If you’re looking for lots of practical advice on managing your circadian rhythms and improving your sleep, I think there are probably better books you could choose than this one. She does give some tips, based on things she herself discovered throughout her research, such as going for a walk in the morning rather than the evening, narrowing the window of time between your first meal of the day and your last, and waiting 90 minutes after waking before drinking tea or coffee. Most of the book, though, is spent exploring the science behind these things. I got bored at times, such as when she goes into a long discussion of photoreceptors in the eyes, but mostly it’s all very readable and often quite gripping. I was particularly fascinated to learn that fruit and vegetables have their own circadian clocks, even after being harvested, and storing them under bright lights can disturb their rhythms, affecting their nutritional value.

The main conclusion Peeples comes to is that not everyone’s circadian rhythm is the same and people’s internal clocks can run slightly differently (some of us are night owls and some are morning larks). We need to find routines and schedules that work for us, but unfortunately the way society is structured can make that difficult, particularly if you’re someone who struggles to wake up early in the morning. Peeples also looks at disruptions to these routines, such as jet lag, and considers evidence of sports teams performing better or worse depending on the direction in which they’ve had to travel through time zones.

The Inner Clock is a long book and contains a lot of information, but I’m sure most readers will find at least some of it useful and interesting, regardless of whether or not you have any problems with your sleep.