As the hours of lost sleep add up, the effects of that deprivation are cumulative; and as it turns out, are far more all-encompassing than just making you feel groggy and ill-tempered.
In fact, your lack of sleep is responsible for a myriad of negative effects on your health and wellbeing.
1. Makes you gain weight
That’s right; your poor sleep habits are causing you to pack on the pounds. Not only does a lack of sleep alter your body’s chemistry — promoting fat storage and lowering your metabolism  — but it’s also behind why your diets keep failing.
Your struggle to stick to your meal plan may have less to do with self-control and more to do with the effect of sleep deprivation on the hormones which regulate your appetite in the first place.
Sleep deprivation causes your levels of appetite-stimulating hormones increase, while there’s a simultaneous drop in those which signal satiety. So, not only do you feel more hungry, but you’re unable to detect when your body has had enough to eat.
While you’re feeling more hungry, don’t expect to be reaching for fruits and veggies! Being overtired increases your cravings for high-fat and high-carb foods, in part because your body is looking for the feel-good effects to counteract the negative mood you’re in. 
2. Ages You
It’s not just those bags under your eyes that are making you look older; a lack of sleep significantly affects the quality of your skin and makes it age faster!
Missing out on a good night’s rest causes more fine lines, more wrinkles, uneven pigmentation and increases dryness.
What’s worse is that over time, chronic sleep deprivation reduces your skin’s ability to repair itself, making it more susceptible to damage from environmental factors such as the sun. 
On top of all this, by altering your hormones, a lack of sleep can increase your acne breakouts.
So, it doesn’t matter what fancy night cream you’re using — if you aren’t getting enough sleep your skin will suffer.
3. Dumbs You Down
Getting little sleep night after night is not making you any smarter.
If your performance at work is suffering, keep in mind that sleep deprivation lowers your ability to concentrate, reduces reasoning and problem-solving skills, and stymies creativity.
This is also the reason that late-night cramming sessions are not effective in preparing you for exams or work presentations.
Sleep plays an essential role in memory formation — it’s during our deepest sleep that our brain works to consolidate the information we have picked up throughout the day to store it as reliable memories. 
It’s not just long-term memory that’s affected, a lack of sleep also reduces our “working memory.” Without the ability to hold and manipulate information in our mind our performance on a multitude of tasks is severely impaired.
4. Kills Your Sex Drive
While you’re not using your bed for sleep, you likely won’t be using it for other activities either. Sleep deprivation is one of the surest ways to kill your sex drive, and not just because you’re too exhausted to do the deed.
Testosterone — the hormone responsible for sex drive in both men and women — is significantly lower in people who are not sleeping enough. Furthermore, in men, low testosterone can be responsible for erectile dysfunction. 
Moodiness is yet another way a lack of sleep will put a damper on your romance: If you or your partner are not communicating well, it’s unlikely you’ll be feeling in the mood for love.
5. Causes Mood Swings
Mood swings are one of the most apparent effects of sleep deprivation: Irritability, mood swings and a general feeling of just being not yourself are common complaints when overtired.
As it turns out, mood and sleep are very closely linked. The cause-and-effect relationship between the two goes both ways: While a lack of sleep results in changes in our mood, our mood likewise has an impact on our ability to get a good night’s rest. 
Thus we end up in a cycle of exhaustion and increasing negative mood. Understandably this affects every aspect of our life: From our work and our interpersonal relationships to our self-esteem and joie de vivre.
6. Makes You Depressed
The effect on your emotions is far more pervasive than simply making your moodier: Sleep deprivation has been linked to the development of depression.
People who suffer from insomnia are 10x more likely to develop depression than those who are getting adequate sleep, and there is a similar increase in risk for those with sleep apnea which causes frequent nighttime awakenings.
Sleep is a restorative state that allows the body and the mind to recover from stressors experienced throughout the day.
When we aren’t given adequate time in this restful state, and in cumulation with the other side effects of lack of sleep on our mood we can be pushed into a state of depression. 
7. Increases Aches And Pains
Ever noticed how after waking from a night of broken sleep your body aches? This is particularly noticeable in anyone with a preexisting condition, such as arthritis or fibromyalgia.
Sleep deprivation has hyperalgesic effects — meaning it increases our sensation of pain. This leads to an overall decrease in pain tolerance, and an increase in our perception of the intensity and discomfort of our pain.
In this way, being overtired not only exacerbates preexisting pain, but research has shown that even healthy people report experiencing more muscle tenderness and musculoskeletal symptoms.
Worse, over time, poor sleep significantly raises your risk for developing these chronic-pain conditions. 
8. Raises Stress Levels
Those of us who sleep less than 8 hours a night consistently report feeling more stressed than our well-rested counterparts.
There’s a combination of both mental and physical side-effects of sleep deprivation that result in this activation of our stress-response. 
One night of partial sleep loss alone is sufficient to raise our body’s levels of the stress hormone cortisol by up to 45%.
A chronically elevated level of cortisol does not only cause us to feel more stressed, but can contribute to the development of a variety of disorders including thyroid problems, weight gain, and — at its most extreme — Cushing’s Syndrome.
9. Weakens Your Immune System
Sleep is essential for the proper functioning of our immune system. Without it, you’re more prone to getting sick and take longer to recover from illnesses.
While we sleep our bodies produce the key ingredients of our immune system, enabling our bodies to stave off infections and fight those which are already active within us.
Research has shown that even vaccines are less effective in those of us who are sleep deprived: Reducing our ability to generate antibodies by a whopping 97%. 
Additionally, inflammatory proteins increase with sleep deprivation which, aside from further suppressing your immune function, increase your risk of developing a myriad of medical conditions.
10. Reduces Fertility
If you’re trying to conceive, you should start by improving your quality of sleep. Not only will you feel less stressed — which can also contribute to fertility issues — but sleep deprivation alone has a significant impact on our body’s hormonal functions.
Prolonged periods of disturbed sleep can cause problems with our circadian rhythms — our natural body clock. This clock is responsible for timing the release of hormones, and when it gets out of sync, it can cause irregular menstrual cycles. 
One of the key hormones involved in ovulation — leptin — is produced while we sleep. Thus, if you’re not getting adequate sleep your levels of leptin will be significantly lower and once again your menstrual cycle will be affected.
Melatonin, which regulates the sleep-waking cycle, also plays an important role in protecting eggs when they are preparing for ovulation. Disruption in the production of melatonin can lead to damaged eggs and increase your risk of miscarriage.
11. Increases Risk Of Chronic Disease
As we’ve discussed, sleep deprivation has many short-term effects on your health. However, in the long run, if you continue to sleep poorly night-after-night you’re putting yourself at risk for developing serious chronic conditions such as type II diabetes and heart disease.
Sleep deprivation can lead to diabetes by altering the way our body processes sugar. Those who sleep less require more insulin to maintain normal blood sugar levels, and over time this strains our insulin-producing cells and can lead to insulin resistance. 
Insulin resistance also plays a role in hypertension. As your body’s levels of insulin rise so does your blood pressure. As a result, prolonged partial sleep loss has been linked to the development of resistant hypertension — a particularly hard-to-treat form of the condition which does not respond to standard medications.
Autonomic functioning, hormonal balance and blood clotting factors are all impacted by sleep loss in a manner which is recognised to contribute to cardiovascular disease. Over time, chronic under-sleeping raises the risk of even otherwise healthy individuals.
12. Causes Accidents, And Even Death
I think we can all agree that being over-tired clouds our judgment. Taken in hand with the changes in our coordination and ability to focus, sleep deprivation makes us much more accident prone.
While clumsiness may not sound like the worst side-effect, there are incidences where a lack of sleep can result in significant injury or even death.
“Drowsy Driving” causes an estimated 100,000 crashes per year in the USA: resulting in 1,550 deaths and 71,000 injuries. These numbers are shocking enough, but what’s even more concerning is that 60% of us admit to driving when sleepy.
Sleepiness has also been linked to an increase in work-related accidents. In the most extreme cases resulting in significant industrial and engineering catastrophes.
The Exxon Valdez spill, the Challenger explosion, and the nuclear meltdown at Three Mile Island have all been linked to sleep deprived workers. 
Conclusion: Start Taking Sleep Seriously
You’ve just read 12 very convincing reasons why you should start taking your sleep seriously. Sleep deprivation — even just partial — is taking a significant toll on your overall health and wellbeing.
Undeniably, changing your sleeping habits is one of the most meaningful lifestyle changes you can make to improve your quality of life.
Wondering where to start? The National Sleep Foundation recommends that adults receive 7-9 hours per night, while teenagers need 8-10 hours and younger children 9-14.
So, if you’re sleeping only 4-6 hours per night, no matter what your age, you’re sleep deprived and putting yourself (and others) at risk.