A study from Finland published this week proves what every parent will already have known from bitter experience. Children who don't get enough sleep can turn into bad-tempered monsters.
Researchers found that children who didn't get eight hours were more likely to become badly behaved and hyperactive. Rather than treating them as ADHD cases, it suggests they should just go to bed earlier.
"We were able to show that short sleep duration and sleeping difficulties are related to behavioural symptoms of ADHD," said Dr Juulia Paavonen.
In children, the impact of lack of sleep is immediately transparent. They get over-tired, unhappy and it ends in tears. A late night is paid for by bad moods the next morning. It really does make children miserable.
Seeing it in my own children always makes me think about what similar impacts sleep has on adult moods. We're better at disguising our feelings, we don't start screaming and howling when we're a bit tired. But it must still be changing our moods.
Children can be incredibly angry when they haven't had enough sleep. So how much of adult bad temper and irritability is attributable to lack of good quality sleep? Is road rage and those crazy angry outbursts you hear in supermarkets fuelled by people who need to get to bed earlier?