Staying up too late can make you less enthusiastic about life the next day, even if you lose just an hour of sleep.
Getting less sleep than normal, regardless of the number of hours, makes people feel less positive and happy, according to a scientific study.
Researchers looked at 154 studies, spanning more than 50 years and involving more than 5,000 people aged between seven and 79, on sleep deprivation.
Sleep restriction, where people got less sleep than normal, was found to significantly reduce their positive feelings, such as enthusiasm and happiness.
People's positive emotions seemed to take the biggest hit when they got four hours less sleep than normal, but they already felt less positive from a reduction in sleep.
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Sleep deprivation was also linked to a higher risk of anxiety and depression, although this effect was smaller.
Dr. Jo Bower, who led the research at the University of East Anglia, said: 'These results are important because people who feel less positive enjoy things less such as seeing friends, going to exciting events or watching their favorite television programme, causing them to have a greater chance of watching. risk of depression.
'They are generally less motivated to socialize and are therefore at greater risk of isolation and loneliness.
'In our largely sleep-deprived society, people often stay up late, and we don't want them to worry about that, but this analysis suggests that less sleep will have an effect on mood.'
The scientific review, published in the journal Psychological Bulletin, shows that people's positive emotional states are unsurprisingly most affected by sleep deprivation, such as being forced to stay awake for a night or several nights.
But researchers also looked at the effects of getting less sleep than usual and waking up during the night.
Perhaps reassuringly, for parents of young children who routinely wake them, the latter was not linked to a significant increase in negative emotions – unlike the other two types of sleep loss.
However, this may be because there were too few studies on this to show a link.
Sleep restriction, that is, less sleep than normal, which can be caused by an unusually late evening or early morning, was also linked to people's emotional responses.
The studies tested this with experiments, including showing people images of distress, such as a snake or someone pointing a gun, or asking them to perform stressful tasks such as mental arithmetic.
People who got less sleep responded less strongly and less negatively, indicating they cared less.
Surprisingly, both a complete lack of sleep and less sleep were associated with a decrease in positive emotions rather than an increase in negative feelings such as sadness or worry.
People typically rated their positive emotions, such as enthusiasm, joy and satisfaction, on a scale in the studies analyzed.
Dr. Bower said: 'Evolutionarily, positive emotions such as enjoyment are good for helping us form social bonds and learn.
'But if we haven't had enough sleep, our cognitive function is reduced, so we need to prioritize things like processing threats.
“That could be why positive emotions are watered down, because they don't have any short-term benefit.”
However, most people in the studies were in their twenties, which could have affected the results.