How Much Sleep Do We Need?

Insomnia sharpens your maths skills because you spend all night calculating how much sleep you’ll get if you fall asleep right now.

 

– Anon

 

In the last blog post, we examined the meaning and anatomy of sleep. It follows then, that the curious would naturally seek to find out how much sleep is needed each night. This question isn’t always asked, however, from the purest of motives, but to see how far it is possible to go to the wire each night as we indulge in late-night binges, or perhaps, even perversely, to use those nights into the small hours of the morning as a source of bravado. 

 

In truth, the answer to this question is not as simple as giving a definite number of hours, although there are sound generalities. This is because each person is different, and sleep requirements depend on our current health status and age. In other words, the amount of sleep needed will vary from one person to another, will alter throughout our lives and will depend on our present health needs. Therefore, while keeping guidelines in mind, we should aim to be in tune with the needs of the body and prepared to adjust our sleep requirements as our body demands.

 

Sleep research has led to the following age-based, suggested guideline for the amount of sleep required for optimal health.

 

Sleep Guidelines By Age

 

    • Birth to 3 months: 14 to 17 hours 
    • 4 to 11 months: 12 to 16 hours 
    • 1 to 2 years: 11 to 14 hours 
    • 3 to 5 years: 10 to 13 hours
    • 6 to 12 years: 9 to 12 hours
    • 13 to 18 years: 8 to 10 hours
  • 18 to 64 years: 7 to 9 hours
  • 65 years and older: 7 to 8 hours 

 

From these guidelines, most of us will have had confirmed what we probably already knew – that we require 7-9 hours sleep per night to function at peak performance.

 

 Even so, if we want to turn around our haphazard sleep habits and reap the benefits of a healthy sleep routine, a deeper understanding of the two basic biological machines that govern our feelings of sleepiness and wakefulness should be taken into account. These are sleep-wake homeostasis and the circadian rhythm, better known as the internal body clock. Each of these mechanisms play a different role in sleep regulation and how alert we feel as the day unfolds.

 

Sleep-wake homeostasis works by exerting pressure on us to feel increasingly sleepy as the day progresses, and by keeping us asleep once we do eventually succumb to slumber. We are all familiar with that creeping feeling of tiredness as the day unfolds. 

 

The circadian rhythm or internal body clock works by arranging our feelings of sleepiness and wakefulness into a sort of daily timetable of peaks and troughs, or ups and downs of tiredness around a 24-hour cycle. 

 

The result of these two components working on our bodies at the same time is that, even though homeostatic pressure goes to work to make us feel more and more sleepy during the course of the day, our circadian rhythm prevents this pressure to sleep from overcoming us and forcing us to succumb to sleep too early on during the day.

 

Since the circadian rhythm organises our increasing tiredness into dips and troughs in alertness, we all have the experience of feeling sleepier at certain times of the day, at specific points on our circadian timetable. For adults this is usually in the afternoon between 1:00 and 3:00 pm and the morning between 2:00 and 4:00 am, with some variations in timing for some of us, and depending on whether we are “early birds” or “night owls”. The converse is true, in that we also notice that there are times in the day when we feel a bit more alert. 

 

The strength of these dips and peaks in alertness will be less noticeable if we have had a satisfactory night’s sleep beforehand and will be more exaggerated if we have not. Put simply, we will feel more equal to the challenges in our day by being in a steady state of wakefulness.

 

The circadian rhythm is itself controlled by a cluster of cells in the hypothalamus of our brains called the Suprachiasmatic Nucleus. This is a bit of a mouthful so, for simplicity, I will refer to this from here on as the SCN. The SCN is designed to be sensitive to light and dark and operates in the following way: 

 

When light falls on the light sensitive area at the back of our eyes it triggers light signals to travel along the optic nerve to the SCN, which responds by sending out a message to our internal body clock to tell us it is time for us to start the day. 

 

The SCN sends messages to other control centers of the brain such as those that regulate certain hormones and control our body temperature. As a result, morning brings about a rise in the hormone cortisol associated with alertness, and a reduction in the hormone melatonin which is associated with sleepiness. 

 

Towards the evening, with the loss of light, the release of melatonin increases and remains high during the night to help to keep us asleep. Our body temperature, having previously dropped during the night hours, begins to rise with the onset of day. Other physiological changes occur as well, but I have only detailed the most essential changes to grasp.

 

There are many events that can mess up our circadian rhythm and throw our body’s equilibrium out of sync. These include international travel and its accompanying jet lag, shift work, not adopting regular sleep patterns, or by routinely putting off sleep as late as possible into the small hours of the night. All these events have only been made possible through recent technological inventions, such as artificial lighting, airplane travel, television, computers, and smartphones, all of which have artificially altered our exposure to light.

 

Now that we understand how our biological sleep machines work, we can take advantage of this knowledge to develop good sleep habits. An awareness of sleep-wake homeostasis enables us to better listen to the signals of increasing pressure to sleep as the day progresses; and a knowledge of the circadian rhythm, governed by the SCN and its sensitivity to light levels should help us to accept the winding down process that occurs as the night approaches and acquiesce to the promptings to go to bed.

 

 Adopting a regular sleep routine, allowing for plenty of time to sleep, and limiting artificial light both at night and in the morning means that we will have the means to get the right amount of daily sleep each of us need to be at our most alert each working day.