The physical and mental health effects of both a good and bad night’s sleep


We often feel ‘out of sorts’ after a bad night’s sleep, yet we feel ready to take on anything after an unbroken eight hours.

The physical effects of a bad night’s sleep

Poor sleep has been linked with weight gain, a greater risk of heart disease, stroke and Type 2 diabetes. A small loss of sleep has even been shown to impair our immune function [1].

The mental health effects of a bad night’s sleep

It has been estimated that 90% of people with depression complain about poor sleep quality [2]. Individuals with sleeping disorders such as insomnia or sleep apnoea, who report significantly higher rates of depression than those without [3].

Poor sleep quality has also been linked to a reduction in your ability to interact socially, with researchers now believing that poor sleep can affect your ability to recognise important social cues and process emotional information, leading to a reduced ability to recognise expressions including anger and happiness[4].

The physical effects of a good night’s sleep

Sleep supports healthy growth and development, whilst healing and repairing our heart and blood vessels. Sleep also helps to maintain a healthy balance of our ghrelin and leptin hormones… those that make us feel hungry or full.

Sleep also keeps our immune system strong and healthy.

The mental health effects of a good night’s sleep

The more tired you are, the more difficult it is to concentrate. When we lack sleep, we find it hard to take in vast amounts of information. Once well rested, you will have a clearer mind and sharper focus.

Sleep can also improve our memory – the human brain has three stages of forming a memory:

  1. Acquisition – introducing new information to your brain
  2. Consolidation – the memory is strengthened
  3. Recall – accessing the information stored.

Acquisition and recall happen when you are awake while consolidation happens when you’re asleep. When you are sleeping, your brain consolidates and organises your memories, which helps you remember what you learned the previous day.

Research also suggests that sleep deprivation makes us more stressed, irritable and we react negatively to minor annoyances and interruptions. For example, a survey from the American Psychological Association found that adults who slept fewer than eight hours a night were more likely to report symptoms of stress than those who slept eight or more hours.

How much sleep do I need?

Individual sleep needs vary, but it is widely accepted that most adults need between seven and eight hours of sleep each night, whilst children and teenagers require slightly more.


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[1] Partial night sleep deprivation reduces natural killer and cellular immune responses in humans

[2] Sleep and depression

[3] The relationships between insomnia, sleep apnoea and depression

[4] Sleep deprivation impairs the accurate recognition of human emotions