Why does lack of sleep make you angry?

Chronic tiredness can leave you feeling stressed, irritable and prone to snapping at those around you

Sleep deprivation is a chronic issue in the UK. In fact, recent research reveals that the United Kingdom is the most sleep deprived country in the world. One survey found that, on average, UK adults get just six hours and 19 minutes sleep per night – well below the eight hours recommended by the National Sleep Foundation.

So chances are you’re probably familiar with the tiredness and lack of energy that comes from a poor night’s sleep. If so, you may also have noticed that a bad night’s sleep can cause your patience to wear thin.

We’re going to take a closer look at the link between irritability and tiredness, asking what exactly it is about a bad night’s sleep that makes us so prone to anger?

The relationship between sleep and anger

Sleep experts believe that the correlation between lack of sleep and increased impatience is due to the part of our brains that deals with our instinctive and primal emotions. This is known as the limbic system.

Within the limbic system, there are two small areas collectively known as the amygdala. The amygdala is the area of our brain responsible for our emotional ‘fight or flight’ response. This response kicks in when we feel threatened, but without logic from elsewhere the amygdala has no idea whether it’s dealing with a genuine threat or a minor irritation.

When the amygdala is on high alert, i.e. when you are sleep deprived, it is primed to react strongly to any situation. This can cause your ‘fight’ response to kick in at the slightest provocation.

Studies show how our brain activity changes with lack of sleep

Research reflects this theory, exploring the changes in brain activity after a bout of bad sleep. One study published in Current Biology explored the impact sleeplessness has on the human emotional brain.

The study found that after just one night of disturbed sleep, people who were exposed to negative imagery saw a spike in amygdala activity. The area lit up on a brain scan, and these participants saw 60% more activity in the amygdala than those who got a full night’s sleep.

The study concluded that a good night’s sleep is necessary in order to give the pre-frontal cortex a say in your decision-making (i.e. the rational area of the brain).

Another study looked directly at participant reactions to uncomfortable situations. This 2018 study from Iowa State University used white noise to create an irritating atmosphere. They then compared the way both sleep-deprived and well-rested participants reacted to the conditions.

The results showed that losing just a couple of hours sleep at night can make you angrier and less able to cope with frustrating situations. Participants who had their sleep restricted showed significantly higher levels of anger.


A calm atmosphere leads to a better night’s sleep

Anger and sleep deprivation can create a vicious cycle. Losing sleep makes you more irritable and stressed, and stress can lead to further sleep deprivation, increasing anger levels.

In order to give yourself the best chance of a good night’s sleep, it’s vital that you create a calm environment in your bedroom. Your sleep environment should be cool and dark. Avoid bringing any screens into the bedroom, including your smartphone, and instead opt for reading or meditation before bed. This will help your body to unwind before you drift off.

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