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Please Sir, can I have another... 40 winks?

How much sleep do you need? The Centers for Disease Control and Prevention advises adults between 18 and 65 to aim for at least seven hours of good quality sleep per night.

Unfortunately, sleeping well is not the necessarily the norm. In fact, according to the National Heart, Lung, and Blood Institute of the National Institutes of Health, 50 million to 70 million American adults either don’t get any sleep on a regular basis or have a sleeping disorder.

Why we need sleep

Although nobody can agree on one single theory as to why we sleep, it is good to have an insight into current theories as they are products of lots of sleep studies and research. Combination of two or more theories might give us a more accurate answer.

Inactivity theory (Evolutionary theory, Adaptive theory)

This theory suggests that sleep was developed in the process of evolution. Scientists argue that animals who were inactive at night were not as vulnerable to predators as those that were moving around. Moreover, nighttime and low visibility increase the dangers of falling down or hurting themselves. It is thought that sleep was just an evolutionary appropriate behavior which proved the most effective and which thus developed further and remained a necessary behavior in most animals.

Energy conservation theory

This theory may be partly related to inactivity theory. It states that considering low energy use during sleep, the main reason for sleep might be energy conservation. Competition for the source of energy could be linked to the survival of the fittest. Also, sleep helps living beings conserve energy at times when they aren’t able to find food easily (at night or in winter).

Our brains consume about 20% of our energy which is significant, and reducing brain activity at least a bit may be beneficial for overall energy saving. During sleep, energy expenditure goes down by 5-10% which is enough to preserve some of the valuable energy. One of the strongest points of this theory is the fact that cold-blooded animals sleep a lot less than warm-blooded animals.

Restorative theory

Growth hormone is released during sleep, and it helps repair and restore cells and tissues in our body. In children, this hormone promotes the growth of the body, which may be an answer to why children need so much sleep.

Studies have shown that complete deprivation of sleep for a certain period can result in death of animals, as they completely lose the defense mechanisms of their immune systems. Our brains need maintenance during sleep because the activity of our nerve cells results in by-products which accumulate more and more over our waking time. The name of this by-product is adenosine and its accumulation is one of the things that make us sleepy. We need to stop producing adenosine in order to clean it up from the brain, and sleep is the way to get this done.

It should be noted that caffeine ‘masks’ our tiredness by blocking the effect of adenosine. This can be bad for our brain health as we lose touch with our natural sleep needs and fail to let our brain do the maintenance, allowing way too much adenosine to build up.

Sleep also helps our emotional stability by letting amygdala, the fear and emotion center in the brain, get refreshed. With sleep loss, our muscles and tissues aren’t restored and memory isn’t consolidated, which makes it more difficult to concentrate and perform physical activity.

Brain plasticity theory

This theory relates to changes in how our brain is structured and organized. We know that in children most brain development occurs during sleep; however, sleeping is beneficial for brain structuring of the adults, too. Some synapses are strengthened and some are not – depending on the importance of information our brain is processing.

As deep, slow-wave sleep is responsible for one part of memory consolidation, rapid eye movement (REM) sleep additionally employs emotional response to learning. One study conducted in Ottawa has shown that French-learning participants had more REM activity and dreamed about communicating in French. Those participants who didn’t experience increased REM made the least progress during the course. Knowing what things are and what they are called is known as declarative memory.

REM also seems to be involved in visual learning, while light sleep stages (stage 1 and stage 2) are important for motor learning – learning how to do things – this is called procedural memory. Brain processes information which requires motor skills like successfully coordinating and performing tasks (swimming, riding a bicycle).

According to the American Heart Association:

Studies show short sleep duration or poor sleep quality, is associated with high blood pressure, elevated cholesterol and atherosclerosis. And habitual short sleep increases the chance of cardiovascular events. Not getting enough restful sleep is also correlated with:

Poor diet / weight gain A study of 495 participants found an association between poor sleep quality, increased food intake and lower consumption of whole grains. And short sleep duration may lead to weight gain, even in those with a low risk for obesity.

Diabetes An analysis of past studies suggests not getting enough Z’s significantly increases the risk of developing Type 2 diabetes. In addition, losing as little as two hours of sleep per day may lead to increased insulin resistance and decreased glucose tolerance in lab conditions. High blood sugar associated with diabetes can also increase cholesterol, blood pressure and triglycerides, ultimately damaging the nerves and blood vessels. As a result, people with Type 2 diabetes are twice as likely to have a heart attack or stroke.

Inflammation In lab studies, sleep restriction is associated with inflammation, and preliminary research suggests this may be true in the general population. This is important because inflammatory processes can elevate risk for cardiovascular disease.

Stroke, heart attack and death Researchers report a modest link between both short and long sleep duration, or nine hours or more at a time, and stroke. Short and long duration sleep are also associated with a greater risk of death.

The link between sleeping disorders and heart disease

Perhaps unsurprisingly, a growing body of research demonstrates a correlation between many sleeping disorders and cardiovascular health.

  • People with common sleeping disorders such as obstructive sleep apnea or insomnia also are far more likely to have heart arrhythmias, plaque buildup, heart failure and coronary artery disease than the general public.

  • Evidence is mounting that neurological sleep disorders such as restless leg syndrome, which affects 7% to 10% of Americans, may increase the risk of heart disease, although more research is needed to better understand the connection.

  • In most people, blood pressure dips during sleep. However, that doesn’t always happen in people with Type 1 narcolepsy. Although more research is needed in this area, some suggest that this may increase the risk for heart problems.

The role of mental health

There’s a similar both-ways relationship between sleep and mental health: People with psychological disorders are more likely to develop sleep problems than those in the general population, and sleep problems may also increase the risk of developing certain mental illnesses.

This may affect heart health. Many studies have shown both daily stressors and traumatic stressful events increase the risk of cardiovascular disease. Loneliness, workplace stress, anger and hostility, anxiety, depression and even pessimism likewise impact overall health, increasing the risk to heart health.

Optimism, on the other hand, is associated with healthier living, including better sleep quality and a lower risk of cardiovascular disease and death from all causes.

In a recent scientific statement, the American Heart Association acknowledged the growing body of evidence pointing to the strong link between mental health, behaviors and physical health, noting data that suggest treating mental health can improve heart health.

What’s the takeaway?

There’s a strong connection between mental health, sleep and overall physical health, specifically cardiovascular health.

Lifestyle factors such as diet and exercise may reduce the risk of heart disease, both directly and indirectly, by fostering better sleep. This, in turn, may lead to a better outlook and more energy – the very best kind of feedback loop.

What should I do if I have problems sleeping?

The CDC advises people to:

  • Go to bed and wake up at the same time every day, weekends included.

  • Sleep in a dark, quiet place set at a comfortable temperature.

  • Ban electronic devices from the bedroom. These can interfere with sleep.

  • Avoid caffeine, alcohol and large meals before hitting the pillow.

  • Exercise. Physical activity during the day makes it easier to fall asleep that night.

Talk with your doctor or health care professional if you have symptoms of a sleep disorder or have tried such measures and still can’t get to sleep.


Why Do We Sleep, Anyway? Healthy Sleep. Harvard. Accessed December 23, 2018.

De Koninck J, Christ G. Language learning efficiency, dreams and REM sleep. Psychiatric Journal of the University of Ottawa. Accessed on December 23, 2018.

Sleep, Learning, and Memory. Healthy Sleep. Harvard. Accessed December 23, 2018.


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