Why your body needs a better night’s sleep

Sleep is as crucial for health as food and air.  While scientists don’t fully understand what is happening in our brains and bodies when we sleep, despite decades of research into this area (a fascinating topic in and of itself), the consequences of chronic sleep deprivation are well known and continue to emerge.  As well-known sleep scientist Professor Allan Rechtschaffen once put it, “If sleep does not serve an absolutely vital function, then it is the biggest mistake the evolutionary process has ever made.”  

Why we need sleep

If you thought that the main consequence of chronic sleep deprivation was, well, feeling sleepy, take note.  The truth is that sleep deprivation can be life threatening, either immediately (most people have heard stories of sleep-deprived drivers falling asleep at the wheel), or more insidiously, robbing us of our good health in addition to years of our lives. 


Multiple studies have linked insufficient sleep with weight gain, with findings showing that those who habitually sleep less than six hours per night are much more likely to have a higher body mass index (BMI), and those who sleep eight hours per night have the lowest BMIs.  Why?  Well, part of the association seems simple enough to explain: if you are very tired, you may be less likely to find the energy to exercise, and you may be more tempted by that chocolate cake (both because your willpower to resist is lower, and because tired people may eat sugar to give them a temporary energy boost).  And yet it’s not simply a problem that can be corrected with greater self-discipline, since being tired makes you biologically more likely to put on weight.  One reason has to do with hormones: during sleep, our bodies manufacture hormones that help us control appetite, energy metabolism, and sugar processing, and too little sleep can upset the balance of these hormones.  Examples of hormones which are secreted excessively when we are tired include leptin, a hormone that regulates hunger, and ghrelin, which stimulates appetite.  Emotional eating may also be more likely, since stress hormones like cortisol are higher when we are tired.


Insufficient sleep can contribute to the development of type 2 (non-insulin dependent) diabetes by influencing the way that the body uses sugars.  To demonstrate this in one study, a group of healthy individuals whose sleep was cut from 8 to 4 hours per night were found to process sugar more slowly than when the same individuals had slept for 12 hours.  Multiple studies have found that adults who usually slept less than five hours per night have an increased risk of diabetes.  In addition, overweight and obese individuals are more likely to have diabetes, so the above ways in which sleep causes obesity will in turn increase your risk of diabetes, as well.  

Heart disease and high blood pressure

If you’ve got high blood pressure, even a single night of inadequate sleep can raise your blood pressure the following day.  As far as your heart health is concerned, it seems that getting just the right amount of sleep is best: a recent study found that sleeping too little (less than 6 hours) or too much (more than 9 hours) will increase the risk of coronary heart disease.  Sleep apnoea, a condition where individuals wake multiple times during the night as a result of the airway closing off (you may well have sleep apnoea if you snore heavily most nights) is also associated with high blood pressure and cardiac disease.

Depression and anxiety

Most of us can relate to the feeling of being at the “end of our tether” after a poor night’s sleep, so it’s perhaps not surprising that chronic sleep issues are associated with depression and anxiety. Of course, depression and anxiety can cause sleep disturbances themselves (like difficulty falling asleep or waking too early), but causality may well work the other way, too, with chronic sleep deprivation contributing towards depression, anxiety, and other mental illnesses.


It’s well known that humans and other animals are less able to fight off infectious illness when they’re sleep deprived, and sleep can be powerfully restorative to the whole body.  Ever wondered why a cold (or other infection) can make you feel so sleepy?  Scientists have discovered that substances produced by the immune system to fight infection can also cause sleepiness: one theory is that the immune system evolved “sleepines inducing factors” because, over the course of human evolution, those individuals who slept more when they were ill were more likely to survive, and thus pass along their genes to the next generation.

Life expectancy

If the above reasons aren’t enough to convince you to get some more sleep, consider this: three large cross-sectional epidemiological studies determined that sleeping five hours or less per night increases your risk of death (from all causes) by about 15%.

Sleepless in Great Britain  

Despite the clear importance of sleep, a full 40% of Britons get by with less than the NHS recommended six to nine hours of sleep per night, with the average amount of sleep at six hours and 35 minutes.  Sixteen percent say that they have used alcohol as a remedy to get them to sleep (alcohol may help you feel drowsy, but it’s an ineffective strategy since it also decreases the quality of sleep), and 47% say that worry or stress keep them awake at night.  Worryingly, a full 33% of individuals get between only 5 and 6 hours of sleep per night, and 7% get under 5 hours per night.  

So what can you do to improve your sleep?

One of the most important things you can do is to prioritise your sleep the way you prioritise other aspects of wellness (sleep is just as important to health as nutritious food and exercise).  Setting a regular sleep/wake schedule, avoiding caffeine late in the day, avoiding exposure to light at bedtime, and getting rid of electronic devices before bed are a few small things that could make a big difference.  If you still find that your sleep is suffering (for instance, if you snore every night, if you can’t manage to fall or stay asleep, or if you are always tired no matter how much you sleep), you would be wise to seek a medical opinion, since there are many medical causes of poor sleep beyond issues with sleep hygiene.

The bottom line

Treat your sleep as a priority, not a luxury, and don't sacrifice sleep to 'get more done', it's a false economy and your body deserves better!


Healthy sleep, 2008. Available from: <http://healthysleep.med.harvard.edu/healthy/>. [5 March 2015].

First Ever British Bedtime Report Launched, 2013. Available from: <http://www.sleepcouncil.org.uk/2013/03/first-ever-great-british-bedtime-report-launched/>. [5 March 2015].