"Not enough shut-eye makes you more impulsive and can fuel addiction," the Mail Online reports. The claim was prompted by a review of evidence into the link between sleep and self-control carried out by American psychologists.
The authors looked at previous research, including studies into how poor sleep affects our blood sugar regulation and apparently exhausts our internal resources and willpower. They suggest poor sleep could extend into poor health and how we function at work, and could even fuel addictive behaviours.
The crux of their argument is that self-control is like physical strength; we don't have an infinite amount and being tired depletes our resources, so other areas of our life may be affected.
The authors linked their findings about the effect of sleep deprivation on self-control to addiction. But addictions have many influences and sleep problems are very unlikely to be the single cause. Even if there is a link, it's just as likely to be the reverse: addictions adversely impact sleep quality.
This article must largely be considered to be the opinions of the authors. No method was provided, so we don't know how they selected the evidence on which to base their discussion. Crucially, other relevant studies could have been missed.
Most people experience problems sleeping at some point in their life, but you should ask your GP for advice if you are experiencing persistent insomnia. You should also seek help from your GP if you think you may have developed an addiction.
Where did the story come from?
The study was carried out by researchers from the Department of Psychology at Clemson University in the US. No sources of funding are reported.
The Mail discussed the findings of this article as fact, but did not consider the limitations of this opinion piece. The paper does not make it clear that the study is an evidence-informed opinion piece, which ranks low on the level of evidence scale. A systematic review would rank much higher as credible evidence.
What kind of research was this?
This narrative review aimed to explore the interactions between sleep habits and self-control.
As we all know, good sleep is essential for good functioning. But, as the researchers say, chronic sleep loss is common for many, and may lead to problems such as inattention and lack of self-control, which includes acting on impulse.
The authors say there have been limited attempts to develop theories to better understand and predict the effects of poor sleep and sleep deprivation. The researchers drew attention to previous discussions of models that were developed to try to understand how sleep deprivation affects performance.
The publication describes itself as a "mini review", and no methods are provided. This implies it is not a systematic review, so the authors may not have considered all the relevant evidence on the topic. This means there is a risk key evidence has been missed.
What are the models of self-control?
One model suggests self-control stems from a few internal resources that become exhausted when we have to repeatedly exert self-control. This is said to be called "ego depletion".
Previous research has shown having low blood glucose causes this, leading to poor self-control when we're hungry. Anyone walking through a supermarket while hungry might be familiar with this sensation. But other things besides blood glucose could contribute to this.
A second model suggested loss of self-control could be related to psychological processes. Some research suggests maintaining self-control could be the result of choosing between competing goals or making priorities, or believing in willpower.
This suggests self-control is largely an issue of correct allocation of effort: you can make a decision not to eat the donut or go to the gym after work, but not both.
Combining the different models gives the idea that self-control is the result of internal psychological resources, and can be influenced by personal choices and beliefs. It is said these models can explain self-control when someone is exposed to a minor stressor that results in mild ego depletion.
In these situations, the person can choose to make a different goal, work on a different task, or choose to believe in their ability to complete the necessary work and overcome the negative effects of ego depletion. But if the person's internal resources have become significantly depleted, they may not be able to exert self-control until these have been restored.
How does poor sleep affect self-control?
Sleep is an example of a physiological necessity that can overwhelm any type of mental effort to resist it. For example, if a person is driving a car when overly tired, they may fall asleep even when psychologically they know the consequence could be death.
Part of the effect of sleep on self-control could be through glucose levels, which go through a cycle with the daily body clock. Research has shown our ability to metabolise glucose is affected by our sleep habits.
Sufficient sleep at night may restore internal resources for self-control, and has also been shown to promote plasticity in the brain – that is, the ability to make new nerve connections, change and adapt.
Previous research has also suggested those who report good sleep have lower psychological strain and better self-control. But there is said to be limited research looking into how poor sleep affects things such as effort, exertion and choice.
One study is said to have shown that when making choices, sleep-deprived people will pick the less challenging options, even if it's as simple as a test of walking – sleep-deprived people walk more slowly. Sleep loss has a negative impact on the person's performance, as well as their access to energy resources.
Other research supports this, suggesting sleep deprivation causes lack of activity in the parts of the brain involved with thinking and planning, so this could impair the person's ability to exert self-control.
How do the researchers interpret their results?
The authors concluded that, "Sleep and self-control form an integrated system that provides the basis for complex decision making and capabilities." They say good sleeping habits could refuel a person's ability to make more difficult choices instead of opting for the easier option.
They go on to say the effects of better sleep and self-control could extend into better work performance and better health, and even help with social issues as addiction, excessive gambling and overspending.
This narrative review, which explored theories on how sleep may influence self-control, will be of interest to psychologists and sociologists.
But no methods are provided on how the narrative was produced, so we don't know how the researchers selected the studies that informed their discussion.
Calling their study a "mini review", it seems unlikely this is a systematic review. This means not all relevant evidence may have been considered, and this article must therefore largely be considered to be the opinions of the authors.
Without clearly defined methods, any review of this type is always vulnerable to the accusation of "cherry-picking" – that is, research that supports the authors' opinion has been included, but research that challenges their opinion has been ignored.
Although the research has linked the effects of lack of sleep on self-control to the problems of addiction, addictive behaviours such as gambling are complex conditions. They can be influenced by many things, including a person's characteristics, personal and social circumstances, and mental health.
Lack of sleep might make a person more likely to give into addictions, but it is unlikely sleep is the single cause. On the flip side, a person with addictions could have poorer sleep as a result of their addiction, or because of various other life and health circumstances associated with this. There is not always a clear-cut cause and effect relationship.
Good sleep is essential. Most of us have first-hand experience of the effects of poor sleep – we don't feel our best and our functioning and performance in many areas can be affected. But getting a good night's sleep every night is not always easy, and many things can affect people's ability to get to sleep or stay asleep.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Mail Online, 3 July 2015
Links to the science
Frontiers in Human Neuroscience. Published online May 11 2015