You would need to have been sleepwalking through life to have missed the memo about just how important sleep is for a healthy body and mind. But as I was researching my new book Brain Power I was surprised to discover just how much of an impact just a small amount of missed sleep can have on our cognitive abilities, something we should all keep in mind as the clocks change this week.

Just take a recent study by researchers in Scotland, who wanted to compare the effect of driving when tired to driving after a few too many. Thirty volunteers were split into one of two groups – one had a good time getting tipsy enough on Sauvignon blanc to tip them over the Scottish drink-drive limit (a similar level too much of the rest of the world) while the less fortunate half of the participants had to go 24 hours with no sleep. They were then all submitted to a driving test simulation and also had to rate how good they thought their ability to drive was before and after drinking a cup of coffee.

Compared to people who were intoxicated with white wine, those who hadn’t slept ended up with slower braking reaction times and less control of the car. Some even fell asleep at the wheel in episodes of dangerous “micro sleeps” that caused them to veer off the road. Surprisingly, caffeine did little to help. Although coffee is often recommended to alleviate the effects of tiredness when driving, including in the Highway Code in the UK, in this study it had no impact on driving skills. Worryingly, in both groups people mistakenly thought that the caffeine hit had improved their ability to drive, giving them a dangerously false sense of confidence. So those of us who drive when we have slept badly should remember that caffeine might make us feel more competent, but that could be an illusion – better to take a nap instead.

You don’t need to pull an all-nighter to feel the effects of lack of sleep on your cognitive abilities; even a small reduction in sleep can have a big impact. The hour that is lost when the clocks go forward in springtime in the US sees a 17 per cent spike in traffic accidents the following Monday morning – and a five per cent rise in heart attacks in the three weeks afterwards, too – suggesting it can take days or even weeks for us to adjust to even an hour less sleep.

How much sleep is enough for you to confidently get behind the wheel? To find out, Brian Tefft at the AAA Foundation for Traffic Safety in Washington, DC recently conducted the first peer-reviewed study to look at how much a person has slept and their risk of subsequently being responsible for a car crash. He analysed a sample of almost 5,500 traffic accidents and found that anything less than seven hours a night can put you at serious risk of instigating an accident. It’s not surprising that driving becomes so hard when we lack sleep: another study found that people who slept less or more than seven to eight hours performed worse overall on a battery of 12 cognitive tests, and sleeping less than four hours the previous night was equivalent to ageing the brain by eight years.

The cognitive toll of being tired doesn’t stop with our ability to operate heavy machinery. The springtime clock change reveals another problematic effect of sleep on our cognition: a lack of it messes with our morals. Moral awareness is important because it involves the ability to detect morality in others, not merely our own judgments. Using a series of tests, researchers in the US and Singapore recently looked at how morally aware people are when they are sleep deprived compared to when they are rested, and found that a sleep deficit of just two hours led to a 10 per cent drop in people’s ability to detect moral elements of a scenario they were presented with. And after the clocks go forward, there is a steep drop in people searching online for words related to morality, such as “unethical”, “fraud” and “honesty”. Chronic sleep deprivation has been shown in lab experiments to increase implicit biases towards minority groups, too, and change how trustworthy we think people are based simply on their facial features.