CHAPTER 10

Sleep and the daily rhythms of life

WHETHER YOU ARE A SEVERE INSOMNIAC, a teenager who never leaves their bedroom before 3 pm, or a siesta-loving Spaniard, sleep is a fascination. Why do we need it? What happens when we sleep? Why did this unusual and potentially dangerous behaviour evolve? It doesn’t seem to make sense, as we are especially vulnerable when we sleep. Is it to do with allowing our brains to dream? Or maybe it’s a time to clear out the garbage from our brains that has built up during the day? And what about the daily biological rhythms of our lives? What are they for? My goal in this chapter is to keep you awake long enough to ponder sleep and our circadian rhythm.

Everybody needs to sleep. When you go without it you become irritable, crave sweet or fatty foods, become a bit loopy and will eventually die. This is true – mice kept awake will die after a few days. It’s not really clear what they die from (other than their brains and hearts ceasing to work), so we can’t find out what sleep is actually for, other than keeping us from becoming very irritable and ultimately dying.

Scientists have known for some time that there are different phases to sleep¹. A machine called an electroencephalograph (EEG) allowed people to see what was happening electrically inside brains. It measures electrical activity, which is read out as brainwave patterns. What is striking is that there are five distinct brainwave patterns during sleep. In the first phase, you are still relatively awake. The electrical wave patterns are small and fast, like rapid ripples on water. These are known as beta waves. The brain begins to relax, and the waves get bigger and slower, as your brain heads to the deep blue depths of sleep. These are called alpha waves, and are observed in Stage 2 of sleep.

NORMAL ADULT BRAIN WAVES WHEN AWAKE AND ASLEEP.

In this stage you aren’t yet asleep, but you might experience vivid dreams, which are called hypnagogic hallucinations. It is this kind of state that hypnotists can induce. They somehow, usually with a calm voice getting you to focus on something like a swinging watch, provoke slow waves in your brain. You become prone to suggestion too, which is why a hypnotist can make you search for a leprechaun, or maybe get you to stop smoking. Sometimes you’ll feel like you’re falling, or your body will writhe suddenly. This is known as a myoclonic jerk, which is actually quite common and has no explanation.

Your brain then moves into the second phase of sleep, which usually lasts about 30 minutes: you are now entering Stage 3 and Stage 4 of sleep. Your body temperature starts to drop (and so you might feel cold and pull the duvet tight). Heart rate also begins to slow during this phase. Your brain is now entering into a deep sleep, a stage that lasts around 30 minutes. The brainwaves are now even slower and are called delta waves. Stage 4 gets you in even deeper. Bed-wetting and sleepwalking occur at the end of this phase, although why these occur then is not fully understood. Finally, your brain enters Stage 5, which is known as the ‘active’ phase of sleep, where something peculiar starts to happen – your eyes start to rapidly move back and forth. This is known as rapid eye movement, or REM for short. Your breathing rate can go up in this stage and your brain will show increased activity again. What’s paradoxical here is in spite of your brain being very active, the opposite is true for your muscles, which are very relaxed.

The REM stage is when we dream, and on average we will enter it 90 minutes after falling asleep. We have no idea why we dream, but theories include that it might have something to do with ordering and storage of thoughts, or more simply a consequence of the slowing down of neurons, which somehow triggers memories to be vivid and jumbled. If undisturbed you will cycle four or five times through these stages in a night.

What is going on here? Why is this highly ordered and predictable course of different brain activities happening? A few theories have been proposed². First is the evolutionary theory, which states that sleep evolved to get us out of harm’s way. At night we might be especially vulnerable to predators, and so we evolved to sleep, where we might retire to a nice warm cave and stay very still. We were also less likely to injure ourselves in the dark. Darwinian natural selection led to this behaviour, which then dominated in the population. We may have survived because our early immediate ancestors evolved to sleep, perchance to dream.

The second idea is called the energy conservation theory³. We fall asleep to save us having to eat, at a time when trying to catch prey is difficult because of the dark. There is some evidence for this. Energy demand drops by 10 per cent when we are asleep. Evolution could work its magic again and randomly select this trait, providing an advantage over those who don’t sleep and therefore persist. The primary function of sleep might therefore be conservation of energy.

THE NIGHTMARE (1791), BY ANGLO-SWISS ARTIST HENRY FUSELI.

Idea number three (they come thick and fast – I hope you’re still awake) is the restorative theory, in which the brain repairs and rejuvenates cells and tissues. This will clear out any debris that has built up during the day. Furthermore, muscle growth, repair of tissues and the making of new proteins all occur more prominently when we are asleep. A good example here is to do with a chemical called adenosine. This is made during the daytime as a by-product of the activity of cells. Its build-up is what makes us sleepy, and eventually fall asleep. There is a ‘drive to sleep’ in response to adenosine. When we sleep we then clear the adenosine. That life-saver of a substance caffeine works by counteracting the effect of adenosine, making us more alert.

When we are young, sleep appears to have an especially important role in brain development. Infants will sleep for up to 14 hours per day, and at least half that time is spent in REM sleep. Lots of electrical activity happens, perhaps akin to a building site where the electrics are being installed and tested.

In 2013 scientists provided evidence for the restorative function of sleep⁴. They have found that when we sleep, the refuse trucks come out in our brains to help clear the debris that build up during the day, adenosine being a prime example of refuse. Our brains work very hard. Neurons are constantly firing, being pared back and interacting with each other via what are called synapses. Chemicals called neurotransmitters leap across synapses in order for one neuron to communicate with another. Neurons also communicate with another important cell type in the brain called glial cells. All this frenzy of activity is happening right now, as you read this stimulating chapter, leading to a build-up of refuse – by-products from all the activity. This refuse is cleared by glial cells, the brain’s garbage trucks.

It’s been thought for a long time that when glial cells go rogue and stop doing their job, nasty proteins can build up. Most noticeably this occurs in Alzheimer’s disease, where a protein called beta-amyloid builds up in a part of our brains called the hippocampus (named after the Latin word for seahorse, due to its shape). It’s a bit like rubbish building up to block a road. In the case of the hippocampus, the build-up affects personality and memory through still-mysterious processes. And remember, scientists love mysterious processes.

At night, however, the sluice gates in the channels of the brain open, and cerebrospinal fluid rushes though, bringing the refuse-collecting cells, and acting to flush out the things that have built up during the day. The refuse is then flushed down to your liver to be digested. What the scientists found was that this process runs twice as fast when you sleep, because your neurons shrink, making the channels between them wider. Scientists have observed tiny fluid-filled channels in the brain. To see them, they had to train mice to fall asleep on top of a two-photon microscope. They then injected a dye into their brains and watched it flowing in the channels.

Also it is thought that the barrier between the brain and the rest of the body, called the ‘blood–brain barrier’, opens a little more during sleep, allowing the refuse to be cleared out of the brain. This is when they saw the increased flow, when the mice were asleep. They also injected a labelled version of beta-amyloid, and could see it being cleared at twice the rate when the mice were asleep. Sleep thereby restores us because it clears out all this junk after a hard day’s thinking. Sleep deprivation and insomnia are known risk factors for Alzheimer’s disease, and we now perhaps know why: less refuse collection, because of lack of sleep, clogging up the hippocampus. So a major function of sleep has been found. Sleep is all about clean-up time, a bit like putting on your dishwasher or washing machine at night. This doesn’t mean that the other functions don’t also occur, as sleep is likely to have a number of functions, all equally important.

MARGARET THATCHER (1925–2013), FORMER BRITISH PRIME MINISTER, IS OFTEN CITED AS NEEDING ONLY FOUR HOURS OF SLEEP PER NIGHT.

Another area of study is the power nap. During the day, we sometimes feel sleepy. This again may be due to a build-up in adenosine, which caffeine can counteract. A power nap can do the trick too, however, and has been shown to be tremendously beneficial⁵. Just 20 to 30 minutes of sleep can reset your system and give you a burst of alertness. Studies have shown an increase in so-called motor skills (for example typing or playing the piano) following a 20-minute power nap. Importantly, though, no more than 30 minutes. If you go beyond that into Stage 3 sleep and then are woken up, you will perform worse at motor skills, including driving. However, higher-order activity such as memory is boosted by a sleep of around 60 minutes, even though you may feel groggy.

Power napping becomes all the more important if you are sleep-deprived. The question that often arises is, how many hours sleep a night is best⁶? This has huge variability. Some need 10 hours and some get away with five hours or less. We are the only species on the planet that we know of that intentionally deprives itself of sleep. Margaret Thatcher, the former British prime minister, is often cited as someone who got only four hours sleep a night. This may in fact be one of the reasons she eventually developed Alzheimer’s disease, although we can’t be sure of that. In a study of 54,269 adults (which is a huge number, and so the averages that emerge are probably correct), 31 per cent slept for six hours or less, 64.8 per cent slept for seven to nine hours and 4.2 per cent slept for 10 hours⁷. Those at either end of this range were more likely to be obese and suffer from anxiety and diabetes.

At any event, many people report being sleep-deprived, especially middle-aged men. Studies have shown that one in five Irish people are sleep-deprived. Sleep deprivation is actually a serious health matter. It leads to a weakening of your bones through osteoporosis. It can be assessed by measuring a protein (P1NP) that is released by your bones when they are strong. Levels of this protein were 28 per cent lower in young men who were sleep-deprived⁸.

Sleep deprivation also increases the craving for junk food, which in turn leads to obesity and all its consequences of increased risk of diabetes and cancer. It could also be a simple matter of time: the more hours we are awake the more time we have at our disposal to eat. Our bodies also make more of a chemical called endocannabinoids. These are your own form of the cannabinoids found in cannabis, and they cause a natural form of the ‘munchies’, which those who have had cannabis will recognise. If you are sleep-deprived you make more of this, and so eat more, again leading to obesity. Instead of smoking a joint, sleep for only four hours a night and you might make your own chemicals to give you a high.

An International Bedroom Poll has been done (now there’s a great title for a survey) across several countries⁹. The US and Japan have it worst, sleeping on average 40 minutes less than people in other countries. The Japanese average 6 hours and 22 minutes, while the Americans average 6 hours and 31 minutes. Germans, Mexicans and Canadians report the longest time asleep, with over seven hours in each country. Every country reports sleeping on at weekends, with an average of an extra 45 minutes on days they do not work.

Other intriguing findings to emerge from the survey were that more than half of Mexicans and Americans pray or meditate before sleep. Apparently 43 per cent of people in the UK have a soothing drink before bed, and one-third of them sleep naked. In most countries, however, at least two-thirds watch TV just before bed, and for many people the last thing they do before sleeping is to check their smartphone. The Japanese are more likely to sleep in the same bed as their children, and people in the US are most likely to sleep in the same bed as their pets. And which country is most likely to have people sleeping with their socks on? The US and Canada again. Perhaps it’s the cold winters in parts of those countries.

Another recent study used an app on its subjects’ smartphones to get an even better picture of sleep habits. This study broadly confirmed findings in the International Bedroom Poll. Other interesting findings were that women on average sleep 30 minutes longer than men¹⁰. Also, the study confirmed that as you get older you need less and less sleep. Sleep patterns varied widely among young people, but in older people the amount of time asleep narrowed to around six hours on average.

Why is there such variation in how much sleep different people need? Why do some people become sleepy at certain times during the day? And why do we feel sleepy at night anyway? Also, why are some people more alert at night (scientists call them ‘night owls’) while others are more alert in the morning (they are termed ‘morning larks’). It all comes down to our in-built biological clock¹¹. The scientific term for how our body changes over the course of the day is ‘circadian rhythm’ – ‘circadian’ meaning ‘about a day’. Just like our ability to look at our wristwatch, our bodies have evolved this neat little system of internal clocks so that our bodies know what time of day it is. Since life began, the Earth has been spinning on its axis, bringing with it the daily changes that we are now so familiar with. Sunrise, sunset.

Our body clock allows us to schedule things at the right time of day. It’s like your internal daily planner. Practically all animals on Earth have it. We are all familiar with this. We feel hungry at certain times, mostly when it’s bright. We feel sleepy at other times, mostly when it’s dark. When we are jet-lagged these rhythms go out of whack, making us sleepy at the wrong time, with disrupted appetite and mood changes. Shift workers also have disruptions in the normal rhythms of daily life, which can in fact damage their overall health. The study of circadian rhythm has relevance to our overall health and well-being, with fascinating aspects being discovered.

First, let’s define the typical events that happen in our bodies over the course of a day. Between 6 am and 9 am, most people wake up. We are of course excluding that strange creature the teenager, who has very different patterns from others. My own mother realised I had entered adolescence when quite quickly I went from a lively young boy, up with the lark, running around and smiling, to a teenager who only emerged from his bedroom after 2 pm. She wondered what had happened to her lovely little boy. But for most other ages, we are all awake by around 9 am. Testosterone also peaks at this time, perhaps to get us ready for the day ahead. However it is also the time when we are at risk of a heart attack, as our blood is slightly thicker and our blood pressure slightly higher.

These changes seem to be to get us ready for the day ahead and prepare us for the activities that face us. Between 9 am and 12 noon, the stress hormone cortisol peaks, which gives our brains a boost of alertness. We tend to be most productive at work before lunch, when our short-term memory is at its best. Our body makes digestive enzymes in anticipation of eating and we feel hungry because of the release of hormones such as ghrelin, which stimulates the parts of our brain that then say ‘you’re hungry’. Between 12 noon and 3 pm, our bellies will be full of food.

And of course once we’ve eaten we experience that familiar early-afternoon slump, the post-lunch dip. Our alertness takes a nose-dive at this time, and there are more accidents on the roads. It’s also the worst time to drink alcohol, as it makes you even groggier. Between 3 pm and 6 pm our body temperature rises slightly, our hearts and lungs work better and our muscles are 6 per cent stronger, so now is a good time for physical work or a workout. Some athletes actually try to get a personal best in sport at this time because of this difference.

THE RHYTHM OF LIFE. WE ARE EFFECTIVELY MACHINES, WITH OUR BODIES AND BEHAVIOUR CHANGING ACCORDING TO A CIRCADIAN CLOCK THROUGHOUT THE DAY AND NIGHT.

Between 6 pm and 9 pm you are ready for dinner. However, don’t leave this too late, as the way the body handles food changes as we get closer to night-time. We are more likely to store food as fat, so it’s a bad idea to eat at night¹². A bag of chips eaten at night will pile on more fat than when eaten earlier. This is in part because we are more active during the day and burn it off, but it also appears to be due to storage of fat being more prominent at night. One useful thing, though, is that our liver can break down alcohol at this time, so now is the safest time to drink. From 9 pm to midnight, bedtime is looming.

This is perhaps the most dramatic thing to happen, as our bodies make our own sleeping tablet in the form of melatonin. When our eyes detect the dimming light, melatonin is secreted by the pineal gland in our brains and makes us fall asleep. When we travel across time zones this gets made at the wrong time compared to local time and so we fall asleep and lose vitality at the wrong time – this is what we call jet lag. Sunlight shining in through our eyes affects its production – it is made in low light, and so eventually our bodies acclimatise in the new time zone.

Blue light suppresses its production and is the wavelength of light emitted from computer screens or smartphones, so it is not a good idea to be looking at devices at night-time if you want to sleep. Shift workers working at night have to defy their own melatonin, and then have trouble sleeping at other times. They are also more likely to be obese, as they eat at night. One reason therefore for the current obesity epidemic is that people have disrupted sleep or are sleep-deprived and are eating at the wrong time.

Melatonin gets made earlier if you are a morning lark and later if you are a night owl, although what controls this isn’t known. Genes that make proteins that control our circadian rhythm, and one called PER2 seems to play a prominent role. PER2 appears to be one of the key cogs in our body clock. If you have one type (called the long type), you will be more likely to be a morning lark, whereas if you’ve the short type you will be a night owl. There is also a condition called familial advanced sleep phase syndrome, where people fall asleep at 7.30 pm and wake at 4.30 am on average. This runs in families, so if you happen to have a family near you with this condition, don’t call around at 7.30 pm, as they will all be snoring. It is caused by a particular mutation in PER2, further highlighting the importance of this protein for controlling our sleep/wake cycle¹³. PER2 and other components are responding to sunlight, which therefore sets our body clocks. It’s almost as if sunlight is the key that winds up the daily spring in our body clock, with PER2 running as the spring unwinds.

The role of sunlight in maintaining our body clocks is likely to be important when we consider seasonal affective disorder (SAD). This is a mood disorder in which people who have good mental health for most of the year have depression in the winter. They sleep too much and have less energy. This is likely to be caused by less sunlight. In the US it affects 1.4 per cent in Florida but 9.9 per cent in Alaska. Similar rates have been reported in Nordic countries. This response may have evolved to make us less active in the winter, when food is scarcer. Light therapy can be a useful treatment for SAD, as can dawn simulation, which involves a device that gives gradually increased light in the morning when it would otherwise be dark. The long, dark winter may limit the production of melatonin, which light therapy appears to restore. Melatonin itself can be a useful therapy.

What is also interesting regarding circadian rhythm and mood is that if you are a night owl, you have a higher risk of depression and cancer¹⁴. Night owls are also inclined to be more outgoing, sociable, narcissistic and promiscuous. One interpretation of this is that it’s to do with what zoologists call ‘mate poaching’ – if you are awake at night and your rival isn’t you might poach his or her partner. Marital breakdown has also been shown to be higher if two night owls marry or if two larks marry. This could be because they get in each other’s way (and on each other’s nerves). The ideal marriage is an owl and a lark, as they will only meet up at certain times, and might have complementary personalities. Perhaps the ability to stagger responsibilities such as childcare and household chores over a longer day leads to harmonious relationships.

Owls and larks to one side, there are some creatures that don’t rely on sunlight to set their clocks. Bristle worms, which live in the sea, use moonlight to set theirs, and sea lice use the tides to set theirs, so any regular environmental cue will do.

From midnight to 3 am you are asleep, and the sluice gates open to flush out the debris from your brain that has built up during the day. If you’re still awake, however, you need to be careful. You may well have the long dark night of the soul, as the hormones in your body are making you feel tired and somewhat low in mood. Industrial accidents are much more common during these hours, for obvious reasons. From 3 am to 6 am you are still hopefully asleep, but melatonin levels start to fall to get you ready to wake up. Your core body temperature is also cooler, as energy is diverted away from maintaining a body temperature at 37°C, to other activities like skin repair.

Sleep may well promote beauty by making your skin look better. The energy might also be needed to keep the flush on in the brain. It has recently been shown that our immune systems are more active at night and less active during the day¹⁵. This seems odd, as we might need our immune systems to defend us when we are up and about, since we might be more likely to get infections. It may be that a slightly less active immune system might stop us from overreacting to mild infections, which can do more harm than good. It is also thought that during the night the immune system is creating memories of what it encountered during the day, so that if we see the same infection again we will respond to it appropriately.

This feature, however, also has consequences for diseases involving our immune system. Rheumatoid arthritis is a disease where our immune systems attack our own joints, causing destruction and pain. It’s worse at night, and people wake up very stiff and sore. Asthma attacks are also more common at night, and again this could be due to an overactive allergic response in our lungs, at the same time when our lung function is at its lowest.

And so, having gone through a 24-hour cycle, we wake up again, to the beat of a drum, or in this case your body clock. This circadian rhythm reveals how we are actually machines, and how our moods, appetites and sleep patterns are governed not by choice but by the workings of clock proteins in our bodies.

There is of course variation in the human population, as the general distinction of the night owl and morning lark reveals. People who need very little sleep and yet appear to be healthy have been the subject of a recent study. A genetic basis for what are called ‘short sleepers’ has been found¹⁶. Many of these people who only need four to six hours a night share a mutation in a gene known as DEC2. Mice that were created with this mutation also needed very little sleep, and when their brains were examined, a very interesting finding was made: they had enhanced connections between the parts of the brain that connect sensation and memory. The mice were also less likely to be overweight, which is similar to humans who are short sleepers. How can they get away with half the amount of sleep as the rest of us? It appears they get more bang for their buck when it comes to sleep. The enhanced connections might enhance the sluicing of debris or allow for memory consolidation, which is thought to be another important function of sleep.

The discovery of this mutated gene promoting short sleep is an intriguing development, and scientists would love to know exactly what it does. It may well be the master regulator of the sluicing, which as we have seen is a key purpose behind why we sleep at all.

Would you like the short-sleep DEC2? What would you do with the extra time it would give you? Who knows, the future might have lots of genetically modified short sleepers, up all night to get lucky, enjoying themselves, and truly seizing the day.

AFTER SLEEPING BEAUTY HITS THE SNOOZE BUTTON FOR THE FIFTH TIME ON HER SMARTPHONE, PRINCE CHARMING INTERVENES.