The Health Impact of Sleep

We are frequently reminded of the need to be healthy – to exercise regularly and to eat well. But something is missing from this advice. One of the most fundamental models of health is called The Three Pillars, which refers to exercise, nutrition and sleep.

The impact of sleep is frequently overlooked, but this article goes into more detail on how sleep contributes to your overall health.

Causes of sleep deprivation

First of all, what causes people to get insufficient sleep? There are several specific sleep disorders, such as insomnia: difficulty falling asleep, staying asleep, or waking up too early. Sleep-related breathing disorders include obstructive sleep apnoea, where your airway repeatedly closes when you sleep, causing you to wake up. The list goes on, though interestingly, the most common cause for insufficient sleep doesn’t relate to a sleep disorder at all. It is caused by something called ‘voluntary sleep deprivation’.

A bit of caution has to be used with this term, as often an individual won’t feel there is anything remotely ‘voluntary’ about looking after their newborn baby or working three jobs to pay the bills. But the term refers to a situation where insufficient time is set aside for sleep. For many people, there’s scope to re-structure the day to allow more opportunity for sleep at night.

But why bother doing this? Aside from the slow brain, low mood and zombie-like feeling that follows a poor night’s sleep, poor sleep in the longer term is associated with developing a wide range of significant physical and mental health problems.

The cardiovascular system

One of the most researched areas affected by poor sleep is the cardiovascular system. This refers to the heart and the blood vessels throughout your body. An extensive study of over 22,000 patients who slept less than six hours a night was compared to controls – people who were like them in every other way except they slept more per night. After ten years, they were followed up. The short-sleeping group were 68% more likely to have had a heart attack and 85% more likely to have had a stroke—a considerable increase.

The Health Impact of Sleep

Poor sleep is associated with other cardiovascular diseases, including high blood pressure, heart failure and irregular heart rhythms.

What causes this? During sleep, your cardiovascular system is much more relaxed. Your heart rate and blood pressure are lower, exerting less strain on the wall of your blood vessels, meaning they are less likely to get damaged. If the average person sleeps for eight hours a night and lives to their mid-70s, then that’s about 25 years spent sleeping. This is a massive chunk of time to spend relative cardiovascular relaxation and contributes to your overall longevity. If you’re sleeping two hours less per night over a sustained period, this impacts the amount of cardio relaxation you’re getting. Heart attacks and strokes, therefore, occur more often.


Diabetes is a condition associated with high blood sugar levels. The hormone that usually keeps your blood sugar within normal limits is insulin. There are two kinds of diabetes – type 1, which is an autoimmune disorder where you are unable to make enough insulin, and type 2, which is when your body still makes insulin, but your cells have become resistant to it. Type 2 diabetes is more likely to develop if you have a high carbohydrate diet, which means your body constantly produces insulin to bring your blood sugar down. Over time, your body stops responding to insulin.

Poor sleep is associated with a much higher risk of type 2 diabetes. Part of this is due to sleep’s effect on other hormones in your body. When you sleep poorly, your body produces more ghrelin. This is a hormone that increases hunger. You also produce less leptin, which is the hormone making us feel full. The result is that you eat more. You are also more likely to have higher cortisol – the dominant hormone in your circadian rhythm’s sleep-wake phase. One of its other functions is to increase your blood sugar levels.

One research study suggested that poor sleep should be seen alongside other more traditional risk factors, such as obesity in the development of type 2 diabetes.


While no bodily systems are entirely unaffected by poor sleep, the brain is probably the most sensitive. This has led researchers to believe that sleep is primarily a neurological process. As well as causing poor concentration and memory in the short term, there’s a longer-term effect on the brain from poor sleep.

The Health Impact of Sleep

Dementia is the name given to a group of symptoms associated with a decline in brain function. This often means poor short-term memory but can also affect how you think and behave. The most familiar type of dementia is Alzheimer’s disease. Overall, dementia affects 7% of people over 65 years old.

Alzheimer’s disease is caused by the accumulation of waste products called amyloid and tau. These waste products are produced by brain activity. They are removed from the brain by a recently discovered network called the glymphatic system. This brain-cleaning network is mainly active as we sleep. It is thought that reduced quantity and quality of sleep means there is less time for the glymphatic system to clean these waste products out, so over several years, they accumulate at a faster rate – which is why Alzheimer’s disease often presents at an earlier stage in people who are habitually bad sleepers.

There are other forms of dementia, such as vascular dementia, where the micro blood vessels to the brain fur up and block, meaning the brain does not get enough blood to function.

Mental health

It has long been known that mental health disorders can affect sleep. Almost all mental health conditions affect sleep in one way or another. Depression is often associated with early morning waking, and anxiety is strongly associated with insomnia and difficulties in falling asleep. However, increasingly robust evidence suggests that this association can work the other way around, with poor sleep causing these conditions.

Part of this causation relates to how some of us may respond to sleep deprivation. Suppose we attempt to compensate by cancelling social meet-ups with friends, missing the gym or phoning in sick for work. In that case, we end up missing important things in maintaining a healthy mental state. However, an independent biological process thought to contribute to the two-way relationship with mental health most likely relates to the REM stage of sleep. REM sleep allows processing emotional thoughts and experiences from the day, so you can better emotionally regulate during waking times. Studies have shown that the onset of depression can be preceded by less and less REM sleep throughout the night.

When mental health conditions can be both a cause and an effect of poor sleep, there’s the potential for each to feed into one other in an escalating cycle. Often the best approach is to address both issues at the same time.

The Health Impact of Sleep

Sleep is a boost to health

While it can be disconcerting to think of the health impacts of not getting enough sleep, it’s just as legitimate to think of it in reverse with the many health benefits of getting a night full of good quality sleep and using it is a motivator to achieve this.

With good quantity and quality of sleep, you give your cardiovascular system a period of nightly rest to help keep it in excellent condition for longer. Good sleep will reinforce your circadian rhythm and regulate the operation of the hormonal systems involved in blood sugar control which staves off diabetes. You will give adequate opportunity for your glymphatic system to clear out brain waste and keep your mind running at full function. And finally, having enough nightly REM sleep will maximise your ability to regulate your emotions and help keep your mental state in the most positive and robust condition possible.

If you are struggling with your sleep, the good news is there are many excellent ways to improve it. Methods can range from re-structuring your day to allowing more opportunity for sleep to diagnose and treat specific sleep disorders such as insomnia or sleep apnoea. It’s also important to mention that sleep doesn’t have to be perfect – don’t underestimate the impact of getting even one extra hour of sleep each night.

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The Health Impact of Sleep