Like all living things, we operate on a daily cycle, and sleep and rest are vital parts of that. Here we'll look at what goes on inside you while you're asleep and why depriving yourself of proper rest can have some surprisingly serious consequences.
Live Well...Be Healthy by Dr. John Marsden and Alison Dillon, (BBC Books, £12.99)
is packed with clever tips, for men and women, to help you to maximise your health and wellbeing. But, don't take our word for it. Here is an excerpt to get you started...
Clocking off
Your body is controlled by approximately 100 complex 'biological clocks', each of which is responsible for regulating different vital functions inside you, such as digestion, temperature, the secretion of hormones, reproduction and growth. Those internal clocks are also known as your circadian rhythms (circadian from the Latin meaning 'around the day'). And remarkably, for reasons we're not yet entirely sure of, your body's clocks all work on a 24-hour timescale.
There's a leader of the pack when it comes to biological timekeeping. That's the master body clock that resides deep within your brain. Here's what happens: information about the current daylight levels around you gets passed from the cells in the retina of your eye through the optic nerve and along to the big daddy of circadian rhythms - that's a group of cells called the suprachiasmatic nucleus (SCN). When it comes to keeping time in the vast orchestra of your brain, the SCN is your very own conductor. On top of daylight levels, it also uses clues from your meal times and other social activities to keep track of time. Then, as day and night pass, it broadcasts vital messages across your brain. These messages trigger the production of a cocktail of important chemicals that keep you and your body 'in time'.
We have drift-off
Let's wind back your life to yesterday evening. As the day drew to a close, you were probably unwinding as you watched late-night TV or made the best of that last glass of wine, but it was a different story inside your body. Your SCN had registered that daylight levels had fallen and sent a message to a tiny cone-shaped structure in your brain called the pineal gland. In response, it began pumping out a special sleepiness hormone called melatonin into your bloodstream. As your melatonin levels rose (which normally happens about two hours before bedtime), you started to feel drowsy, your core body temperature dropped and you began to feel ready for sleep.
Once under the covers, most of us take around 20 minutes to drop off and then every 90 minutes or so your brain cycles through five distinct sleep stages. The first two stages are fairly light and you can be woken easily if disturbed. Then, as the electrical activity in your brain is progressively dampened down, complete relaxation takes over and you enter the deeper third and fourth stages. Finally you reach the fifth stage - REM (rapid eye movement) sleep - which occupies a quarter of the night. Your eyes will dart madly back and forth under your eyelids as your brain goes full-tilt into electrical overdrive and begins experiencing highly emotional dreams.
Meanwhile back to last night - deep in your veins, that soporific hormone melatonin probably peaked between around 2 and 4 a.m., insuring that your distinct sleep cycles continued through the night. But while you were hopefully happily exploring the land of nod, there wasn't much rest for your master timekeeper, the SCN. As this morning broke and the light began to rise, it had to be on call to send a wake-up message to another gland in your brain, called the pituitary. The pituitary gland is part of a complex brain circuit (called the HPA or hypothalamic-pituitary-adrenal axis). A cascade of chemicals gets produced along this path, which ends just above your kidneys at the adrenal glands. Here, adrenaline and cortisol get pumped out - chemicals that raise your heart rate and blood pressure, make you feel alert and help release energy. So, as your cortisol level rose with this morning's light, it put paid to the sleepy effects of last night's melatonin and your brain began to wake up. And just to help you along the way, the pituitary gland did its morning chore as your very own in-built alarm clock - within 30 minutes of first waking, it had triggered a cortisol boost of a massive 100 per cent to ensure you didn't doze off again (in theory, that is, if the well-worn snooze button on most alarm clocks is anything to go by).
How much shuteye is enough?
Scientists have estimated that a century ago, people living in industrialized cities got around nine hours of sleep a night. Nowadays, with our longer working hours and night-time light pollution, the average for city-dwellers is somewhere in the region of less than seven hours. That means you'll spend about 25 years of your life asleep!
So is sleep doing its job for you - and what exactly is the point of it in the first place?
The early sleep experts wondered whether the behaviour had originally evolved to keep our ancient ancestors out of trouble in the darkness of night on the African savannah. But as people's bedrooms have proved to be relatively safe from roving jungle predators for some time now, that doesn't exactly explain it. Instead, the more likely explanation is that sleep's refreshing and regenerative effects allow various brain, hormonal and growth processes to take place inside you. Essentially, sleep gives your brain and body uninterrupted time to get its biological duster and rubber gloves out and get down to its own special version of internal housekeeping.
Getting into sleep debt
If you think of sleep as time that could be spent more usefully doing something else, what's coming might - ironically enough - be a bit of a wake-up call. Here's what really happens to your body as it gets deprived of sufficient resting time. At first, despite feeling tired after one or several nights of compromised sleeping time, you'll probably be able to carry out most simple tasks relatively well in short bursts. But the real problems begin when major concentration is required. Your judgement will be affected, your social and communication skills will suffer and you'll be far more likely to make bad decisions all round. You might get grumpy and irritable or take unadvisable risks in your daily life, even down to little things like crossing the road against the traffic lights or putting your foot down in the car to get somewhere on time.
While the effects on your mind might be more immediately evident, over time lack of sleep will start to take its toll on your body. Your appetite will increase to compensate for your body's growing need for energy - which obviously could lead to weight gain. On top of that, scientists in the US have shown that people who often get less than six hours' sleep a night seem to have much more sluggish metabolisms. Compared to eight-hours-a-night types, the short-sleepers' bodies are only about 60 per cent as efficient at using their hormone insulin to break down glucose (sugars) in the blood into energy. They also need to use a whopping 50 per cent more insulin to carry out that vital metabolic process in the first place. In fact, that's not far off what goes on in your body if you're in the early stages of diabetes.
Metabolic go-slow
One possible explanation for this worrying metabolic go-slow can be found in your brain's timekeeping system. Remember the pineal and adrenal glands and the see-saw relationship between their products, the sleep hormone melatonin and the alertness hormone cortisol? If you're regularly not getting enough sleep, your cortisol levels will be raised. In fact, even one night of sleep loss is enough to hike your cortisol levels up by a staggering 45 per cent the following day. To cut a long biological story short, cortisol evolved as part of our ancient and instinctive 'fight or flight' response. In other words, it's part of your body's very own emergency alertness response. As well as being your early morning chemical wake-up call, it also comes out to play whenever you encounter the daily stresses of life, whether that's gridlock at rush hour, an almighty row with your partner or problems at work.
If one of our stone-age ancestors had unexpectedly come up against an angry big beast, it would have made good biological sense for his body to prioritize the processes going on inside him as quickly as it could. He would clearly have needed the alertness, energy and muscular blood supply to run for the hills or fight the predator off, but other bodily functions, such as getting on with the tough job of digesting last night's wildebeest leg, would suddenly have become somewhat less important. So cortisol, combined with the better-known chemical adrenaline, helped our ancestors get out of sticky situations, partly by giving them the energy to fight or escape, but also by temporarily switching off functions like the metabolism, the immune system, growth and reproduction so that their bodies could get on with surviving in their 'eat or be eaten' world.
Time out
As well as making adjustments to our sleeping environment and behaviour before bedtime, we also need to find ways of including more relaxation in our lives generally. Set aside more time for sleep and rests if you can. If you're the kind of person who actively enjoys yoga, pilates or the occasional massage, the chances are your sleep and energy levels are probably pretty good. But for most of us, hectic schedules don't always permit such treats. Instead, we rely on an annual vacation to pay off our accumulated sleep debts. Sleeping for just two extra hours each night for a fortnight can neatly erase 30 hours of sleep loss. Combine that with the all-round relaxation of a change of scene, climate and a break from work and other chores and a holiday looks like the ideal way to break your stress-fatigue cycle.
Extracted with kind permission from Live Well...Be Healthy by Dr. John Marsden and Alison Dillon, (BBC Books, £12.99)