SLEEP (Part 1): Why Do We Need to Sleep Eight Hours per Day? Malaise caused by Impaired, Insufficient Sleep: A Community Education Feature

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Sleep is the 3rd pillar of good health, alongside diet and exercise

Early to bed and early to rise, makes a man healthy, wealthy and wise (ref)
Sleep is the best meditation                         ...Dalai Lama


Humans spend about a third of their lives sleeping.  
There has to be an evolutionary reason.  

Why do we need to sleep so much and what advantages we derive from it?  
Or one can turn the question around and ask 
what happens if we do not sleep enough or sleep poorly?

PART-2 on  The Science of Sleep & Circadian Rhythm  may be reached here.

Historically, most people thought of sleep as a dormant, switched-off state of the body - an unproductive time. However, recent research has established the relevance of sleep for humans and animals with the clear message that sufficient sleep (7 to 8 hours) is not only important for our physical and mental health/welfare, but a lack of sleep has many unwelcome serious consequences. 

(Click on a slide to see its full page image. Press ESC to return to text)

It is not only that many adults do not get enough sleep, the quality and regularity of sleep in lot of people is relatively poor.  Many adults are curtailing their sleep or obtain 'low-quality' sleep  in response to increasing demands and lifestyle changes, such as prolonged working hours, increased environmental lighting, introduction of new communication technologies, which enable living 'round the clock'.  A National Sleep Foundation Survey in five OECD countries found that 20% of the working population sleeps less than 6 hours per 24-hour day. (see also and also).  

In the following sections, I shall present some disturbing findings as to how sleep deprivation (length or irregularity or both) affects our health and well-being. 

Sleep and Productivity:  Rand Corporation Report (2017) estimates that sleep deprivation of workers has serious impact on a country's GDP:

   Country                          GDP Loss 
                              billion US $        % GDP
    USA                         411             2.28
    UK                             50             1.86
    Japan                       138             2.92
    Germany                    60             1.15
    Canada                      21             1.35

Sleep and Mortality:  One might think that sleeping longer than 8 hours or using drugs to help you sleep (hypnotic medication) will be the solution.  That will be a big mistake.  Both choices have been shown to be extremely harmful and significantly increase the odds of premature death. 

Sleep and Traffic Accidents/Sports Injuries: 

Sleeping less than the recommended amount adversely affects neuro-cognitive performance; verbal and visual memory, co-ordination, reaction time are seriously affected. The impairment in these abilities is higher for greater sleep deprivation.  
In adults, sleep deprivation manifests itself as slower than normal reaction time, reduced alertness/concentration, shortened attention span, forgetfulness, poorer memory, involuntary sleeping (microsleep) lasting from a few seconds to a few minutes etc. 

I discuss two examples in the following:

In their 2016/17 report, AAA has published a detailed analysis of police-reported serious vehicle crashes in the USA during the 2005-2007 period. The study indicates that there is a significantly higher crash risk for drivers who slept for less than 7 hours in the past 24 hours; and also for drivers who slept 1 or more hours less than they usually sleep. 

A similar effect of sleep deprivation is observed in incidences of sport injuries in teenagers.

A recent study (March 2019) found that moderate-to-severe insomnia more than tripled the college athletes' risk of concussion, and excessive daytime sleepiness - even just a few days a month - more than doubled it.  The chance of getting a sports-related concussion during the next year was 14.6 times higher for those with both insomnia and excessive daytime sleepiness than for those who were well rested. See also.  See here and here.

Insufficient/poor quality sleep seriously affects the elderly who tend to sleep 6 hours or less.  It is not correct that old people can manage with less sleep  - they also need 7 to 8 hours sleep per day but for various reasons are unable to do so.  This has serious health consequences as we shall discuss in the following sections.

The modern society puts lot of obstacles in young childrens' sleeping patterns.  Using electronic screens (TV and smart phones) near bedtime disturbs the circadian rhythm and can cause difficulty in falling asleep.  To attend school at 9 am, most children wake up by 7 or 8 am - leaving insufficient time to get the recommended sleep of 10 to 11 hours for primary school pupils.  

Physiological Effects of Sleep Deprivation:  The quantity and quality of sleep is important for our physiological health. Sleep deprivation has been linked to many health problems like obesity, cardiovascular disease (CVD),  depression, type-2 diabetes mellitus (DM), ADHD and Alzheimer disease (AD).  I shall discuss some of the evidence in the following:

Sleep and Obesity:  Many studies in animals and humans have found good correlation between sleep deprivation and weight gain.  Essentially, lack of sleep slows the metabolic rate - even a couple of hours loss of sleep can reduce metabolism by 5 to 20%.  Sleep-deprived humans also show increased appetite - particularly, for calorie-rich carbohydrates. When you are sleep deprived, you have more grehlin (hormone that tells you when to eat) and less leptin (hormone that tells you when to stop eating).  More grehlin and less leptin equals weight gain that can lead to obesity. 

Sleep and Diabetes:  Weight gain and obesity are implicated in the rising number of diabetics.  Sleep deprivation increases the likelihood of gaining weight leading to diabetic condition.  
In a study, healthy young men were sleep deprived for 4 hours on six consecutive nights.  Their average blood glucose level increased by 270 mmol/L (or 15 mg/dl) and insulin response to glucose was 30% lower – essentially they became prediabetics (thankfully reversible) after just six days of sleep deprivation. Changes in metabolic and endocrine (hormone production) functions, driven by impaired sleep, predisposes individuals to clinical diabetes.

The following slide suggests that sleep deprivation may be an independent risk factor in the development of diabetes.

Sleep and Hypertension:  Restricting sleep durations has been shown to raise blood pressure and heart rate.  Chronic sleep deprivation can raise the average 24-hour blood pressure with the result that the cardiovascular system operates at a higher blood pressure, thus increasing the risk of hypertension.

Timing of sleep can also disrupt your body-clock (circadian rhythm) and lead to increased blood pressure by disturbing heart function.  

Sleep and CVD:  Current data indicates that people with impaired sleep are at higher risk for cardiovascular (CVD) and cerebrovascular disease (strokes) - regardless of age, weight, smoking and exercise habits. 
The slide shows the situation for adult population:

The association between long duration (9+ hours) and CVD may be explained by other factors - for example, depression, low socio-economic status, unemployment, low level of physical activity and undiagnosed health conditions have been shown to be associated with long duration of sleep. The association between long sleep hours and CVD may be reflecting the role of long sleep as a marker, rather than a cause. A 7-year study of weight reduction, healthy diet and increased physical activity supports the view that long sleep may be an indicator of risk that can be successfully managed.
Sleep is equally important for the young as well.  Adolescents who do not sleep well are at greater risk of developing ailments related to CVD.  Sleep deprived teenagers were observed to have higher cholesterol levels, higher BMI, higher blood pressure  - all indicators of major health issues in later life. 
For a recent review click here

Sleep and Cancer:  Evidence on the association between sleep duration and cancer risk is controversial, with findings showing inverse, positive, and null effects.  A recent (2018) review of the available information indicated that neither short nor long sleep duration was significantly associated with cancer risk. I refer you to this very extensive study, available online, for more details. 


Sleep and Mental Health:  Sleep and mental health are closely connected. Sleep deprivation affects one's psychological/emotional state and can lead to mental health problems; conversely, people with mental health issues find it difficult to get good quality sleep (Likelihood of  a psychiatric patient to suffer from sleep problems is about 5 times greater than somebody without mental health issues).

The most common sleep problems are insomnia (difficulty in falling or/and staying asleep), sleep apnea (waking up frequently due to disordered breathing like snoring etc) and nacrolepsy (falling asleep suddenly during the day).  Studies have found that, in both adults and children, lack of good quality sleep can directly contribute to  mental health illnesses like depression, anxiety etc. 

The brain basis of a mutual relationship between sleep and mental health is not well understood. Studies suggest that a good night's sleep helps mental and emotional resilience, while chronic sleep disruptions set the stage for negative thinking and emotional vulnerability.

Sleep and Alzheimer Disease (AD):  Incidence of AD, and dementia in general, has increased in the past few decades and the projections do not make comfortable reading.  AD is an irreversible, progressive brain disorder that slowly destroys memory and thinking skills, and eventually the ability to carry out the simplest tasks.
At present, there is no cure for AD and the burden of care of AD patients puts large demands on the society.  The infographic from the World Alzheimer Society is quite revealing about the seriousness of the dementia epidemic.  (Click here for the full report). 
The brain of AD patients is found to have many abnormal clumps of proteins (amyloid plaques), tangled bundles of fibrous proteins (tau tangles) and severe loss of connections between nerve cells (dead neurons). 

Hippocampus (essential in forming memories) is affected first.  As neurons die, other parts of brain are affected and by the final stages of AD, the brain tissue has shrunk significantly.  Genetics, lifestyle and environmental factors play a role in AD but the detailed mechanisms are still not well understood.

There are 47 million people living with dementia worldwide with numbers projected to nearly double every 20 years, increasing to 75 million by 2030 and 131 million by 2050!  The cost of dementia is huge - in 2018, the global cost of dementia is estimated at US$1 trillion rising to $2trillion by 2030.

There is mounting belief among research scientists that sleep problems and Alzheimer's pathology may be connected. Multiple studies have shown that people with dementia often experience sleep disturbances, and other studies, using positron emission tomography (PET), have shown build-up of amyloid plaques in the brains of adults and animals who slept poorly or had inadequate sleep. The following shows the possible connections:

The glymphatic system (brain's sewage network) is responsible for removing the metabolic debris that is produced in a functioning brain.  Amyloid protein molecules are part of the debris.  The cleansing of this debris is done in the night when you are deeply asleep. During the non-rapid eye movement (NREM) sleep (more on it in Part 2), glial cell size is reduced by 60% allowing the cerebro-spinal fluid (CSF) to efficiently flush out the amyloid and tau proteins and other stress molecules produced by neurons.  
In sleep deprivation, the cleansing process is inefficient with the result that amyloid proteins collect and form sticky plaques around the neurons and cause them to die.  


In this Part 1, I have listed some of the health implications of sleep deprivation.  There are other issues, e.g. effect on reproductive system, infection rates, immune system etc. where sleep deprivation can have serious negative effects.  A good reference to learn more about this subject is the book entitled 'Why We Sleep' by Matthew Walker.

In part 2, I intend to look at the nature and science of sleep and its relation to the body clock (circadian rhythm). We shall discover that it is not only the duration of the sleep that matters but also the time of the day that we sleep.

Final Word:  In the '24-hour' world, sleep is a precious commodity.  Long distance travel, shift work, school start times, smart phones, TV in bedrooms, long work and commuting hours disturb the body clock and distort the sleep/wake cycles.  Ever stayed in a hospital overnight? The constant traffic in the wards and check-ups make it impossible for the patients to get rest - not helpful for their recovery.  The relevance of sleep in the maintenance and promotion of good health is not appreciated/acknowledged by the modern society  - even health professionals never discuss this issue.  

Collectively, the modern society is sleep-walking into the vicious circle of sleep deprivation and poor physical and mental health. 

A footnote about the studies referred to in this blog.  Most data on sleep duration was self reported by those taking part in the study - this may be problematic sometimes.  Wrist-worn actigraphy bracelets are non-invasive and provide much more reliable information about sleep.

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