Sleep deprivation seems to be a scourge of modern life with up to 30% of adults reportedly affected by the problem.
In a previous article I’ve discussed the importance of sleep and the reasons why it needs to be a high priority for those who want to maximise their productivity.
In my professional experience the sleep deprived generally fall into two camps – those who don’t really appreciate the importance of sleep and therefore don’t prioritise it (my previous article was for you!) and those who are well aware that sleep is important but sometimes struggle to get enough.
Those of you in this second group no doubt weep inwardly when you read yet another article written by a health professional stressing how your health and happiness are going to suffer as a result of lack of shut eye.
For many people, the classic advice about improving sleep is difficult, if not impossible to implement. For example, I often advise people to aim to go to bed and wake up at the same time each day. Whilst this does help, it is not always practical.
My typical working week involves at least one night shift and I also do 12 hour shifts in A&E so I certainly don’t follow my own advice on this one!
However, I have found that a basic understanding of the science behind sleep has helped me to develop ways of coping effectively with the impact of shift work and to make small, easy lifestyle adjustments which help to ensure that I still generally manage to feel well –rested and energised. In this article I explain a little more about the science and in future articles in this series I’ll discuss which sleep hygiene advice I stick to, which I disregard occasionally and why. I’ll also give some tips specifically for coping with night shifts.
There are a number of medical problems that can adversely affect sleep and I will focus more on these and on medical treatments for insomnia in a future series. Although some of the information given here may be useful for people with those conditions, this series is aimed more at people who are generally healthy but are aware that they don’t always sleep as much or as well as they would like to.
What is Sleep?
Considering the recommendation that we should spend around a third of our lives asleep, surprisingly little is fully understood about why we need sleep and exactly what happens to us during those night time hours.
The Oxford English dictionary defines sleep as the natural condition of rest with unconsciousness and relaxation of muscles.
Studies of the brain waves and eye movements of people who are sleeping have revealed two main types of sleep – REM sleep and NREM sleep.
Non-rapid eye movement or NREM sleep is characterised by little or no eye movement and different brain wave patterns from REM sleep. NREM can be further subdivided into 4 types of sleep, two of which are associated with ‘light sleep’ and two with ‘deep sleep’.
The practical difference between light sleep and deep sleep is that people can be relatively easily woken from light sleep and will generally feel reasonably alert if woken from this type of sleep. On the other hand, it is very difficult to wake someone from deep sleep and they will typically feel drowsy and disorientated on waking. Deep sleep is important for physical restoration. During this stage of sleep the pulse rate, breathing rate and blood pressure drop and brain waves also slow down. It is during deep sleep that the body releases growth hormone, essential for growth and for the repair of damaged cells.
REM or rapid eye movement sleep is characterised by small fast brain waves and rapid eye movements – hence the acronym. There is temporary paralysis of the arm and leg muscles and it is during this stage of sleep that dreams occur. During REM sleep the pulse, blood pressure and breathing rate rise again.
REM sleep is thought to be particularly important for mental restoration and it is during this sleep phase that short term memories are stored as long term memories. People who have insufficient REM sleep may struggle with concentration and learning and may find creative tasks more difficult.
During a typical night adults rotate through these various stages of sleep in cycles each lasting roughly 90 minutes.
Usually we initially fall into a period of light sleep lasting up to 30 minutes before falling into a period of deep sleep lasting 20- 40 minutes. We then return to a light sleep for 5-10 minutes before entering a brief period of REM sleep before the cycle repeats.
During the earlier parts of the night the deep sleep parts of the cycle are typically longer than REM sleep. However as the night progresses this tends to reverse with periods of REM becoming longer and deep sleep sometimes disappearing from the cycle altogether.
What makes us sleep?
There are two main factors governing our hours of sleep and wakefulness: sleep drive and circadian rhythm.
The term ‘sleep drive’ refers to a person’s desire to sleep. It typically increases the longer someone has been awake. The feeling of being tired -that no doubt all of us recognise- is caused by a build-up of a chemical called adenosine in the brain. The longer we are awake the more adenosine builds up in the brain and the harder it is for us to stay awake. The only thing that can ultimately overcome sleep drive is sleep! Most people feel sleepy after around 16 hours awake and find it almost impossible to resist sleep for more than 48 hrs.
Even when people outwardly seem to be awake, after about 16 hours of wakefulness (less for those with pre-existing sleep deprivation) people have brief, involuntary periods of ‘micro-sleep’ in which the brain is temporarily ‘zoned out’. It is thought that these periods of micro-sleep account for the observed increase in accidents in the workplace amongst night shift workers compared with colleagues working daytime shifts. It is also the likely reason that people who drive after more than 16 hours awake have been found to have slower reaction times and worse concentration than those who have blood alcohol levels at the maximum legal limit for driving.
The term circadian rhythm refers to the body’s internal clock which governs the times of day when we naturally feel most inclined to eat, work or sleep. For most people this follows a repeating cycle lasting approximately twenty four hours.
The circadian rhythm is governed by a part of the brain called the supra-chiasmic nucleus (SCN) located within the hypothalamus. The SCN responds to light signals from the eyes to produce the changes in hormones and body temperature which help us to be awake during daytime and asleep at night.
There are two main hormones involved in regulating circadian rhythm: cortisol and melatonin.
Cortisol is the body’s ‘waking’ hormone and is released from the adrenal glands. It acts to increase blood sugar and blood pressure priming us for action. Typically cortisol levels tend to begin to rise from around 6 am reaching a peak at around 9-10 am and fall gradually throughout the afternoon and evening. Cortisol levels tend to be at their lowest around 4-5 am accounting for the slump in energy that many night workers experience around this time.
Extra cortisol is also released at times of stress which is one of the reasons stress can make it difficult to sleep.
Melatonin, the body’s sleeping hormone is released from a part of the brain called the pineal gland in response to a reduction in light. It helps to us to both fall asleep and stay asleep. Typically levels of melatonin rise from around 9pm reaching a peak at around before falling sharply at around 6-7 am and remaining low or even undetectable through the daytime hours.
In addition fluctuations in body temperature (typically a variation of about 0.5 degrees Celsius) throughout the 24 hour cycle affect when we feel most sleepy. We tend to feel most sleepy when the body temperature drops. Typically the body temperature rises slightly just before waking and stays reasonably stable throughout the morning. There is a small drop in body temperature between approximately 1- 3pm which accounts for the post-lunch slump that many people experience. Body temperature then rises again throughout the afternoon reaching peak around 6pm which explains why people can feel just as alert in the evening as earlier in the day even though they have been awake for longer. Body temperature typically stars to drop again around 9-10 pm and is at its lowest around 5 am – another reason that time can be so challenging for night shift workers.
The greater our level of sleep deprivation, the more sensitive we are to fluctuations in alertness due to circadian rhythm.
Generally we sleep best when our sleep drive and circadian rhythm are well synchronised – i.e. if we have been awake for long enough for sleep drive to have built up at a time when the body clock is best primed for sleep.
When sleep drive and circadian rhythm are working against each other, for example with shift work or jet lag, falling asleep and staying asleep can be more challenging.
In an ideal world we would all develop sleep routines that ensured that our sleep drive and circadian rhythms were perfectly matched – however in the real world this is often not possible and in my next article (29/06/18) I will explain which sleep ‘rules’ I sometimes break and how I compensate.
Sleep is just one of the areas people can choose to work on during my Live Better, Feel Better, Be Better programme – contact me for further information.