It’s 3am, you have to be up in four hours, and your mind is whirring. How am I going to get through the morning without my medically mandated eight hours of sleep? Reaching that “magic number” – and how we achieve it – has become something of an obsession in our digitally-tracked society.
In September this year, the UK Biobank & PLOS Medicine study of 95,000 people confirmed that six to eight hours of sleep is the healthiest duration range. “The problem is, we have become slightly obsessed with trying to achieve the ‘perfect’ night’s sleep,” says sleep consultant Maryanne Taylor. “Going to bed at the right time, not waking up, getting a good sleep score... this is not a realistic view of sleep for most people.”
It’s not just about the number of hours you are resting, but the quality of that rest that counts. Dr Jane Rhodes, neuroscientist and leader in biotechnology, says: “Experts are increasingly believing it’s the depth of sleep that matters,” she says. “Seven to eight hours is still the target, but we’ve stopped thinking about sleep in just one dimension. What you want is enough sleep, at the same time every day, with the deep sleep stages [in the first half of the night] intact.”
A rough night’s sleep does not only affect how tired you feel the next day. “A bad night costs you your mood and your concentration,” says Rhodes. “But a bad decade costs you your blood pressure, your waistline and possibly your memory.
“Memory is the fastest casualty. Lose a night before learning and you can’t lay memories down properly: one Harvard study showed that sleep-deprived volunteers were up to 40 per cent worse at forming new memories than rested ones.”
And yet much of the advice around sleep can be confusing and contradictory. Until recently, for example, it was thought that skimping on sleep during the week and catching up with Sunday lie-ins was bad for our health. Then, a recent study presented at the European Society of Cardiology questioned this advice and suggested that a weekend lie-in of an hour and a half can, in fact, protect against high blood pressure.
So what are we to do? Here, the experts reveal the latest science about what your sleeping habit is doing to your body.
The weekend snoozer
If you’ve been doing the early Monday-to-Friday shift, it’s entirely understandable to want to mute the alarm on Saturdays. “We’ve traditionally been negative about weekend lie-ins because big shifts in sleep and wake times can create ‘social jetlag’, effectively moving your body clock backwards and forwards,” says Taylor. “But this study does add some nuance.
“Having said that, it doesn’t prove that having a lie-in itself prevents high blood pressure, or that you can regularly sleep too little during the week and make up for it at weekends,” she says. “For me, the useful message is that a moderate lie-in after a sleep-deprived week is not something to feel guilty about. Some catch-up sleep is fine, but it becomes less helpful when timings fluctuate significantly.”
The early bird
“Bed at 9pm, up at 5am is eight hours,” says Dr Jane Rhodes. “On paper this is close to ideal: enough sleep, consistent timing, and the deep-sleep-heavy first half of the night happening at the same time every night.
“Early risers get morning daylight almost by default, which is the strongest anchor for the body clock,” she says. “They’re also sleeping in step with the social world, so there’s no Monday morning clash.” Some people naturally fall into this sleep pattern, “But if the 5am start isn’t your biology but your commute, and you’re not actually asleep by 9pm, you’re just a sleep-deprived person,” says Dr Rhodes.
The night owl
“Going to bed late and waking late is not necessarily unhealthy,” says Taylor. “Some people naturally have a later chronotype, so they naturally become sleepy later in the evening and prefer to wake later.”
The problem for night owls is often the mismatch between their natural body clock and their daily schedule. If your body isn’t ready for sleep until 2am but your job means you have to get up early, you can gradually become sleep deprived.
“This can lead you to get up early during the week but sleep and wake several hours later at weekends,” says Taylor. “You can adjust your body clock to some extent, but you can’t ‘fix’ a chronotype. Someone who has always been a night owl is unlikely to suddenly become a natural early riser.”
The frequent waker
Waking during the night is not automatically a problem. “We naturally move through different sleep cycles and brief awakenings, often without remembering,” says Taylor. “But where this does become a problem is if awakenings are frequent or prolonged and you feel unrefreshed next day.”
Frequent waking may be a sign something else is going on. A respiratory condition called sleep apnoea can cause repeated awakenings as your breathing stops and starts during the night. Loud snoring, gasping, morning headaches and significant daytime tiredness are all signs that this should be investigated. “Menopause, pain, alcohol, frequent urination, restless legs, room temperature or stress can also cause disturbances, so look at why you are waking,” says Taylor.
For Dr Rhodes, fragmented sleep is a clue that you are experiencing less restorative sleep. “Every arousal pulls you up out of deep sleep, and each comes with a spike in heart rate and blood pressure,” she says. “A broken night hits memory directly. You can spend seven hours in bed, surface 20 times without fully waking, and consolidate very little of the day before. Then there is clearing – fluid flow through the brain, flushes out metabolites and neurotoxic proteins like amyloid-beta and tau implicated in Alzheimer’s disease.”
Dr Rhodes’s company, AstronauTx, is working on pharmaceutical solutions to encourage deep sleep, and to lower the risk of cognitive decline.
The five-hour survivor
“Almost nobody who thinks they thrive on five hours actually does,” says Dr Rhodes. “A 2003 study published in the journal Sleep showed that people restricted to six hours or fewer accumulated cognitive deficits night after night while their subjective sleepiness plateaued. In other words, you stop feeling worse while you actually keep getting worse.”
The self-test: if you rely on an alarm, need caffeine to get going, doze off on trains or in meetings, or sleep dramatically longer on holiday, you’re sleep-deprived, not a short sleeper, explains Rhodes. “There are people averaging four to six hours of sleep with no measurable cognitive or health cost, but under one per cent of the population.”
Taylor says: “When we talk about a healthy night’s sleep, it’s less about box ticking and more about getting enough sleep, reasonably consistently, to feel and function well during the day.”
Miranda Levy is the author of The Insomnia Diaries: How I Learned to Sleep Again