Up until only recently, sleep was thought to be a relatively passive process and its importance in health and the prevention of disease had been overlooked. However, we now have plenty of science to illustrate poorer health outcomes in those that do not get enough of it.
Sleep is the bedrock upon which the other pillars of lifestyle such as nutrition, physical activity and stress management are built. With a refreshing night’s sleep, we are more likely to make better food choices with a reduced intake of hyper-palatable sugary and salty foods. In addition, we feel more energised to partake in physical activity and our stress levels are reduced. There is also evidence linking more quality sleep to a reduced risk of cardiovascular disease and Alzheimer’s dementia.
What Makes us sleep?
The way in which we sleep is under the influence of our ‘Circadian Rhythm’. This is our natural internal sleep-wake cycle which is controlled over a period of 24 hours. Our circadian rhythm is regulated by small nuclei in the middle of the brain known as the Suprachiasmatic Nuclei (SCN). These SCN act as control centres and are connected to other parts of the brain. Together they control our circadian rhythms along with other body functions.
Light seems to play the largest role in setting our circadian ‘clock’. A pathway runs from our eyes to the SCN which regulates our daily cycle. Exposure to natural light first thing every morning will aid this and subsequently facilitate better sleep when dark at night.
Hormonal factors can also influence our sleep-wake cycle:
Cortisol is a hormone, best known for its role in the stress response. It normally peaks one hour after we wake up and then gradually declines throughout the day getting to its lowest point around midnight. If a person is chronically stressed, then the individual can find sleeping more difficult.
Melatonin is also important in sleep. It is a hormone which is released from the base of the brain. Unlike cortisol, we need elevated levels of circulating melatonin levels to sleep well. There is a natural increase of melatonin level throughout the day, but bright lights and modern-day electronic devices (see below) can suppress melatonin release.
In addition, the powerful chemical compound Adenosine, which is linked to digestion also plays an important role. As adenosine builds up in the bloodstream, it signals the body to become drowsier. Caffeine, however, is an adenosine blocker – attaching onto receptors that adenosine would normally bind to and prevents drowsiness from occurring.
Other factors which may have an impact on our circadian rhythm include age, body temperature, metabolism, lifestyle and work (particularly in shift workers).
The 4 Stages of Sleep:
Each sleep cycle lasts around 90 minutes, and we typically go through 4-6 cycles per night. There are four stages. The first three are referred to as non-REM sleep and the fourth sleep stage is REM (Rapid Eye Movement) Sleep.
N1: This is the dozing off phase and typically lasts 1-5 minutes.
N2: This corresponds to a more relaxed phase when there is a drop in body temperature as well as slowed breathing rate and heart rate. The duration of N2 can be between 10 and 60 minutes. As we first settle down to sleep early in the night N2 is short but lengthens later on as the night progresses. We roughly spend half our sleeping time in N2.
N3: This is known as deep sleep and typically lasts 20-40 minutes. It is more difficult to wake someone up in this phase. The body will relax even further with reduced muscle tone, breathing and heart rate. This phase is important for restorative sleep, recovery, growth, repair and for our immune system. It also confers benefit to critical thinking and our memory.
REM sleep is thought to be essential to the cognitive functions of memory, learning and creativity. Brain activity during this phase is increased to levels near that to those when we are awake. This helps to explain the often vivid dreams we have during this stage. During REM sleep the muscles excluding those of the eyes and respiratory muscles become completely paralysed. REM sleep may only last a few minutes during early sleep but with later sleep cycles can last up to an hour. REM sleep is essential for forming emotional memories, learning and creativity.
How can we Improve our Sleep?
(1) Avoiding blue-light emitting devices is recommended 90 minutes before bedtime. This will ensure melatonin levels are kept elevated to increase drowsiness at night. It can be tempting to sleep with the phone in the room and use it as a crutch to get to sleep in bed, but this can affect sleep quality and the overall circadian rhythm. Consider simple hacks like leaving the phone charger in a different room if it will help.
(2) Avoid caffeine after 2pm. As discussed above caffeine will impact on the circulating effect of adenosine which will reduce drowsiness levels. It is worth noting that the half-life of caffeine in the bloodstream after ingestion is roughly between 5 and 6 hours – this is the time taken for the caffeine in the blood to drop down to half of its original concentration. If already taking a lot of caffeine within a day, gradually reduce to avoid rebound headaches.
(3) Minimise alcohol before bedtime. Many people often use alcohol as a sleeping aid. However, we know that though it can have sedative effects, it results in a more disrupted sleep, causes shorter sleep cycles and affects REM sleep quality.
(4) Expose yourself to outside light at the start of the day. This involves actually going outside rather than exposure through a window. Even if dull outside the lux of the outdoors will be brighter than indoor lights. Doing this will prime your circadian rhythm. Conversely dimming lights an hour or so before bed will also be helpful.
(5) Keep temperature of the home between 18 degrees and 19.5 degrees Celsius during the night. A warm bath or warm non caffeinated drink just before bed can be helpful because thereafter our body starts to cool which can facilitate sleep.
(6) Maintain regular physical activity. Aerobic exercise, Resistance training, yoga and tai-chi have all been shown to have benefits in relation to sleep. Vigorous exercise however can increase adrenaline levels and increase core body temperature, so this is probably best to avoid just before bedtime.
(7) Have a regular sleep-wake routine. As well as sticking to a relaxing routine prior to bed, it is important to try and go to bed at around the same time daily. If unable to get to sleep within 15 minutes, go into a dimmed room and do another activity like reading until you become sleepy and can retire back to bed. Waiting for sleep to come to you will only result in further anxiety which will prevent you nodding off.
Getting up within an hour of the normal wake up even at weekends is also important to avoid disruption to the circadian rhythm.
(8) Ensure a diet rich in Magnesium due to links of deficiency and poor sleep. Ensure a plentiful supply of green vegetables, nuts, seeds, legumes and wholegrains. Fatty fish also contains a rich supply if not vegetarian. We can all make efforts to sleep more effectively by focusing on quality rather than quantity of sleep. Someone spending 10 hours in bed can still feel unrefreshed on waking. Of course, secondary factors may also cause disruption of sleep such as stress, anxiety or a new parent having to attend to their child. If possible, with secondary causes of poor sleep, it is important to try and target the root cause. Despite the above measures, chronic insomnia, defined as difficulty falling or staying asleep for at least 3 nights of the week for more than 3 months, will require further attention from a doctor. Similarly, reported episodes of night-time apnoeic spells (where breathing stops), associated with snoring and excessive sleepiness during the day requires further medical attention to rule out obstructive sleep apnoea.
‘Why We Sleep’ – Professor Matthew Walker and related studies