Sleep is an essential function that allows the body and mind to recharge, leaving the person refreshed and alert when woken up. But how much sleep do we need?
Good quality sleep helps the body remain healthy, stave off diseases and promote proper brain function, allowing abilities to concentrate, think clearly and process memories. Sleep loss of a mere couple of hours can reduce performance following the second night.
According to a worldwide survey of 1 million people, on average, we get 7 hours and 12 minutes sleep each night. However, there is a wide variation in the actual requirements: “Long sleepers”, like Albert Einstein, who needed 10 hours sleep each night, or “Short sleepers”, like Margaret Thatcher who only needed 4 hours sleep per night. The amount of sleep needed per night by an individual is driven by a number of factors but at its core it is genetic.
The need for sleep builds during the waking hours. This is known as sleep propensity. Sleep propensity is strongly linked to the time since the last sleep. Sleep plays an important role in the recover alertness, memory consolidation and physiological recovery. There are different stages of the sleep cycle. Stages 1 and 2 are drowsy and light sleep. If woken during these stages, the individual often does not recognise they were asleep. Stages 3 and 4 are slow wave deep sleep. This is when the recovery of alertness occurs, which means that in order to properly recover alertness, an individual needs to be asleep for a sufficient amount of time to move to these later stages. All these stages of Non-Rapid Eye Movement Sleep are associated with the slowing of physiological activity such as heart rate and breathing.
In contrast Rapid Eye Movement (REM) sleep, breathing and heart rate is increased and the brain is active. This is the stage of sleep that is associated with dreaming and also when procedural memory is consolidated.
What factors affect the amount of sleep needed?
Aside from genetics, age and culture have the biggest impact on the amount of sleep needed. Residents of countries in the Far East such as Japan, South Korea, Philippines and Malaysia spend less than 6 hours and 45 minutes in bed each night. By comparison, New Zealand, Finland, Australia and Belgium spend an average time in bed of more than 7 hours and 30 minutes. Interestingly, there is a link correlation between the wealth of a nation (GDP) and the amount of sleep. Residents of most rich countries (Luxembourg, Norway, Ireland, Switzerland and the US) tend to be more rested. But this relationship breaks down in Japan and Singapore.
What about age?
Total sleep time and total nightly amounts of sleep stages vary with age, as do the amount of time spent in each sleep stage. This means the increasing age reduces the amount of recuperative slow wave sleep. The Sleep Foundation have published guidance on the recommended hours of sleep. During infancy the recommended sleep is between 11 and 17 hours per day. This falls to between 7 and 9 during adulthood.
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With the average sleep being 7 hours and 12 minutes, this means that many adults are not meeting their sleep needs.
Knowing the general recommendation for sleep based on age can be helpful. However, amongst these general trends based on age and culture, there are many individual factors that affect the need for sleep. These include activity levels, overall health and work patterns.
What affects sleep duration and quality?
Whilst we may try to get our “full quota” of sleep, there are many factors that affect the duration and quality of sleep. Each of these detract from the recommended hours of sleep and will affect our mental and physical performance. Fatigue is cumulative and it can take around three nights to return to normal after a single “bad night’s sleep”. We already know that age is a factor, but what are other factors affecting sleep?
- Alcohol
- Time of day
- Time since last sleep
- Circadian Phase
- Medication
- Pain
- Stress and anxiety
- Caffeine intake
- Environment
- High or low temperatures
- Bright light
- Noise
- Sleep disorders
- Insomnia
- Sleep apnoea
- Periodic leg movements
- Narcolepsy
- Work/rest patterns
- Shortened rest periods
- Sleep interruptions
- Family disturbance/demands
- Long commutes
The effect of each of these factors are specific to the individual and so understanding how these affect you are a good start to knowing your own sleep needs. In doing so, you might also consider the following:
- Are you productive, healthy, and happy on seven hours of sleep? Or have you noticed that you require more hours of sleep to get into high gear?
- Do you have other health issues? Are you at higher risk for any disease?
- Do you have a high level of daily energy expenditure? Do you frequently play sports or work in a labour-intensive job?
- Do your daily activities require alertness to do them safely? Do you drive every day and/or operate heavy machinery? Do you ever feel sleepy when doing these activities?
- Are you experiencing or do you have a history of sleeping problems?
- Do you depend on caffeine to get you through the day?
- When you have an open schedule, do you sleep more than you do on a typical workday?
We have been undertaking sleep and occupational fatigue research for over 50 years. We conduct our own research as well as supporting our clients characterise and understand sleep profiles, fatigue effects and occupational risk.