How much sleep should you be getting? Ask a room of people and the majority will likely give you the standard reply: eight hours. Quickly followed by an acknowledgment they rarely get all eight. Or often, in fact, even seven. So where does that figure come from – and do we need to be worried if we don’t hit it?

“You’d normally say six hours sleep is a sleep-deprived condition,” explains Dr Andrew Bagshaw, co-director of the University of Birmingham’s Centre for Human Brain Health. “Because for nearly everybody, that’s not enough sleep. There are some people who say they can have four to five hours and feel fine, but that’s pretty unusual.”

So six is less than ideal – but it’s not clear that perfection is necessarily eight hours. “There are two schools of thought,” says Dr Rebecca Robbins, a researcher specialising in sleep at NYU Langone Health in New York. “There’s one camp that says there’s a recommended duration amount of seven to eight hours per night. And there’s another camp that says seven or more hours.”

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The NHS states most adults need between six and nine hours of sleep every night. But, argues Dr Robbins,  there’s evidence to suggest the more narrow window of seven to eight hours per night offers optimal health benefits.

“Cardiovascular disease risks go down,” she says, “general risks for cold and flu go down, mood is improved.” Perhaps one of the most valued benefits, she adds, is the impact it has on your physical appearance. “You look more refreshed,” she says – something many of us recognise anecdotally.

“You could take pretty much any aspect of health and at some point it would be linked back to sleep,” says Dr Bagshaw. The immediate implications of getting too little sleep – with which many of us are all too familiar – include feeling more irritable and anxious, struggling to remember things or make decisions, and of course, looking as knackered as you feel.

But there are also long-term health outcomes of sleep deprivation, which include a disrupted immune system (so you’re more likely to get ill), weight gain and long-term mood disorders like depression and anxiety. It can also increase the risk of obesity, type 2 diabetes, cardiovascular diseases and high blood pressure – ultimately leading to an early death. 

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“People who sleep five hours or less have a lower survival rate,” says Malcolm von Schantz, Professor of Chronobiology at the University of Surrey. But, there’s also a flipside: “People who sleep more than nine hours have a lower survival rate as well.”

Because while having too little sleep can impact health, there is also evidence to suggest that you can sleep too much. A study of more than 116,000 people looked at incidences of heart disease, stroke and death over a period of eight years, along with participants’ reported sleeping times. 

People who slept between nine and 10 hours per night had a 17% increased risk of negative health outcomes compared to those who slept for the recommended six to eight hours, while those sleeping more than 10 hours a day had a 41% increased risk. The researchers also found a 9% increased risk for people who slept six hours or fewer.

Professor Alice Gregory, author of Nodding Off, says there is no ‘one size fits all’ when it comes to the amount of sleep that we need. For example, our sleep requirements change as we get older, she says, and adults appear to need less sleep than children. “Even within age-groups, it seems that certain people need more sleep than others,” she continues.

“Having said this, there are general guidelines about the amount of sleep required – and these have been published by the [US non-profit organisation] National Sleep Foundation. They are based on experts reviewing a large number of studies on sleep length and health.”

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The National Sleep Foundation’s (NSF) recommendations for appropriate sleep durations depending on a person’s age:

Newborns (0-3 months): 14-17 hours each day

Infants (4-11 months): 12-15 hours each day

Toddlers (1-2 years old): 11-14 hours each day

Preschoolers (3-5 years old): 10-13 hours each day

School age children (6-13 years old): 9-11 hours each day

Teenagers (14-17 years old):  8-10 hours each day

Younger adults (18-25 years old): 7-9 hours each day

Adults (26-64 years old): 7-9 hours each day

Older adults (65+ years old): 7-8 hours each day

But while guidelines are useful, there comes a point where obsessing over sleep can actually scupper our chances of a good night’s kip – especially if you can’t get those golden eight hours and it’s stressing you out.

“Thinking too much about your sleep is quite detrimental,” says Dr Bagshaw. “One of the issues people with insomnia have is a concern about their sleep and whether they will be able to sleep tonight, and that’s detrimental to them achieving it. So I think in a way, having an explicit ‘you should be aiming for eight hours’ can be unhelpful if you’re taking it too seriously.”

If that’s the case, should we just forget everything we know and go back to basics? In short, listening to our bodies rather than trying desperately to stick to the advice.

“For an individual I’m never completely convinced that it makes sense to suggest an individual number [of hours of sleep],” says Dr Bagshaw. “Some people need more, some people need less. It’s about you as an individual getting to grips with what you need.”

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He continues: “You’ve got subjective and objective aspects of sleep – you can measure the number of hours, the quality of sleep, but at the end of the day what matters is how you feel at the end of it. It would seem to me to be as simple as: when you get up in the morning, do you feel you’ve had as much sleep as you’d like?”

When it comes to bedtime, experts advise not going to sleep until you feel tired – there’s no point sitting in bed at 9pm, wide awake, because you were worried about getting enough sleep. But if you fall asleep in situations like sitting in the back of a moving car, or feel the need to nap during the day, it’s likely you’re not getting enough sleep at night. Likewise, if you wake up and find you’re irritable or groggy.

“Essentially the hallmark for a good night’s sleep is if you feel well-rested in the morning,” says Professor von Schantz. “If you feel rested after five hours, six hours, seven, eight or nine – that’s great and you should not worry. But if you sleep less than you’d like to sleep, and you feel the negative effects of it in terms of your mood and ability to function, then it’s worth looking into.”