Rhythms of Life
by Russell Foster; foreword by Leon Kreitzman
Profile, £20, pp292
Do you want your handshake to be firm when you are first introduced to the new director? Make sure you arrange the meeting for between 6pm and 8pm. Faced with a crucial but complicated dilemma, time the decision-making moment for noon. The best hour for lovemaking is at 10pm (your wakefulness levels are at their peak) and most natural childbirth will happen between 4am and 6am, just as dawn is breaking.
Our bodies move to a daily rhythm which governs every single gesture and hormone, but about which we are stupendously ignorant. Ticking away inside each cell is a highly intricate timepiece, its genetic pendulum swinging steadily on, regardless of the frenetic lives we lead.
Our sluggishness, our running speed, our susceptibility to pain, our liver's ability to process alcohol - every bodily function, down to the strength of our handshake, is governed by this rhythm.
Even teenagers who are unable to get out of in the morning now have an excuse: apparently, an error has crept into the hard-wiring of their internal body clock. It is known as delayed sleep-phase syndrome, but don't panic - they grow out of it eventually.
Circadian rhythms initially came under scientific scrutiny from the French astronomer Jean Jacques d'Ortous de Mairan in 1729. He wondered why the leaves of mimosa plants went rigid in the day and drooped at nighttime. He had stumbled upon one of biology's central facts - that plants, insects and mam mals move to a daily rhythm that is determined by their internal body clocks, not the environment. It would be another 230 years before the process was given a name.
This intriguing and highly detailed account of circadian rhythms takes us through the research that has been done on many species to show how they learned to optimise time to greatest effect. How else could organisms meet so many competing challenges, from migration to hibernation, from mating to reproduction? By having a 24-hour pattern built into their biology, and modulated, or 'entrained' by the changing light of dawn and dusk, animals were able to survive and adapt to their climate.
The central driving force behind the human clock is a tiny cluster of cells, known as the suprachiasmatic nuclei (SCN) which lie towards the front of the brain. For a while, scientists didn't know whether it was the SCN itself that was the clock, or simply a link in the chain. In fact, it was to take 20 years before they could establish that the nuclei were the control mechanisms for the timed release of hormones. Melatonin is mostly produced between 4am and 6am; your blood is thickening two hours later, as is your fight or flight response, which had a clear advantage for cavemen as the morning light grew stronger and predators appeared.
But what has become clearer down the years is that it's not a one-way street- there is feedback from behavioural changes that fine-tunes the clock. The amount of light we receive in some way 'trains' our internal pacemaker which is adjusted accordingly.
From the moment that electric light first came into our homes, humans have been able to overcome the dominance of night and day. You could argue that this control really began when cavemen first found a way of making fire to ward off wild beasts. But what Foster, professor of molecular neuroscience at Imperial College London, and Kreitzman, a writer and broadcaster, make strikingly clear is that we don't beat it at all.
The problems begin when your lifestyle means less sleep, and that starts to conflict with the circadian patterns to which your body is screaming to align itself. Even if you lose a few hours' sleep during the course of the week, you will clock up a 'debt' because your body has its own invisible sleep accountant totting up the hours lost. Lying-in over the weekend won't be enough to make up the shortfall.
There are two different rhythms which govern the day: the circadian drive for 'wakefulness', which reaches a peak towards midday - the best time for concentration and difficult decision-making - and the 'homeostatic drive' towards sleep. These two processes cross each other's path in the mid-afternoon, the time when sensible societies used to allow citizens to take a nap. A double espresso or a blast of fresh air is the modern way of overcoming this. But then we pick up again, as our wakefulness drive goes into full swing. At 10pm, we are surprisingly alert, with most of us not drifting off until 11pm.
The book makes a convincing case for saying that timing is all, and that if you want to cure certain diseases, you have to give the therapies at the right time of day so that they are absor and metabolised to greatest effect. Just as levels of hormones change constantly throughout the day, so do the chances of being struck down with particular illnesses.
Gall-bladder symptoms are most likely to appear between 2am and 4am, migraines tend to come on between 6am and 8am, and osteoarthritis is worst in the early evening. We spend millions of pounds on developing better surgical techniques or new therapies but we are not using the one we have in the best way.
Their conclusion is bleak - it speculates that we are moving further and further away from the natural order, conjuring up the spectacle that soon we will have soldiers who can fight for 24 hours at a time, supported by bio-engineered drugs. 'It is not too far-fetched to imagine that in the next few years we will learn how to manipulate our circadian rhythms and so disconnect ourselves from the natural world,' they state.
Most human-made disasters, such as the Titanic or the Exxon Valdez, take place in the early hours, at a time when we should all be sleeping, not trying to manoeuvre ships. As the book points out, we have a very linear view of time, and the only way we now know seasons is by looking to see whether there are Christmas puddings or Easter eggs on the supermarket shelves.
