How did you sleep last night? It’s something we assess on waking every day, some people consider themselves good at it, others struggle. And the general consensus has long been that around eight hours is an ideal amount. Experts largely agree that this is the average needed for a restorative sleep, but new research is suggesting that too much sleep could be more detrimental than not having enough. So what are the fundamental rules when it comes to sleep and how many hours do we really need?
What are the different stages of sleep?
Not all time spent asleep has the same effect. A carefully balanced distribution of every stage of sleep – of which there are four – is the key to achieving the right level of restorative rest. According to Dr Matthew Walker, professor of neuroscience and psychology at the University of California, and author of the international bestseller Why We Sleep, certain stages of deep sleep – otherwise known as REM (rapid eye movement) and non-REM (NREM) – are key for the nightly recovery of, and to maintain the health of our body and brain. The four stages of one sleep cycle are:
Stage 1: NREM sleep
This lasts for five to 10 minutes. Your body is starting to relax and you’re easy to wake.
Stage 2: NREM sleep
This lasts 10 to 25 minutes. Your heart rate is starting to slow and you’re in a light sleep.
Stage 3: NREM sleep
Lasts 20 to 40 minutes. This is the crucial deep (or slow wave) sleep phase – it is key for regeneration and body repair and determines whether you feel refreshed the next day. (If you are woken from this stage, you will feel groggy.) You will be less responsive to external stimuli, and more difficult to wake. As we age, the time spent in this phase decreases.
Stage 4: REM sleep
The REM phase is another deep sleep phase, but your brain is far more active. Brain activity, in fact, is not dissimilar to that of waking hours. You are most likely to experience sleep talking, night terrors, sleep walking and vivid dreams during this stage.
Each cycle takes around 90 minutes, so typically we’ll go through four or five cycles in one night. The first sleep cycles of a night have relatively short REM sleeps and longer periods of NREM deep sleep, but later in the night REM periods lengthen and NREM time decreases, ie. while the mind becomes more active, the body enters deeper rest.
How does a lack of sleep affect our health?
Walker believes we are suffering from a global sleep deficit epidemic and he’s not alone, the WHO has declared a “sleep loss epidemic throughout industrialized nations”: “In the 1940s, the average American adult slept seven hours and 49 minutes a night. Now it’s down to six hours and 31 minutes. In the UK the average is six hours and 49 minutes, and in Japan, it is an average of six hours and 22 minutes.” One of the factors contributing to this decline in sleep has been the rise of technology and the need to be permanently switched on. And the results of not enough sleep are worryingly high risk.
Research has shown that stage three of NREM sleep in particular is important for flushing toxins out of the brain, including beta amyloid, the substance associated with brain diseases – it’s interesting to note that Alzheimer’s and dementia have been linked to sleep disorders. “Different cognitive systems and networks undergo restoration during the deep sleep stage,” Walker explains. “Learning and memory systems are transferred from short- to long-term memory during sleep. Preventing you from forgetting, in other words, establishing longer storage sites.” Conditions such as depression can also be substantially affected by sleep. The part of the brain responsible for processing emotions, the amygdala (which controls fight or flight), is regulated by the pre-frontal cortex, which is directly affected by sleep.
And it’s not just the brain that feels the effects of a lack of sleep. Sleep also regulates insulin, blood glucose and blood pressure levels. Plus, Walker adds, those who sleep for five hours or less a night are 200-300 percent more likely to catch a cold than those who average eight hours.
Is too much sleep a potential problem?
New studies suggest that having too much sleep can be just as detrimental to health as too little. According to the Journal of American Heart Disease, those sleeping longer than 10 hours a night, on average, can be at a higher risk of heart attacks and cardiovascular disease in comparison to those sleeping seven hours a night. “Women with cardiovascular problems are particularly at risk,” says sleep neurologist Dr Neil Stanley.
To reap the benefits of sleep, the body needs to complete all of the stages listed above, within full sleep cycles. Sleeping for too long disrupts the body’s circadian rhythm (your internal clock), hindering this restorative process. “Too much sleep can be up to three times more dangerous than having too little sleep. The body likes routine, and sleep is about balance. If you’re sleeping too much, you will feel groggy when you wake up [which signifies you have woken up mid-cycle, and therefore missed out on essential restorative benefits],” explains Stanley. “You can’t catch up on sleep,” he adds. “If you deprived yourself of sleep, you make up the next night with very very deep sleep because your body is stressed and desperate to sleep. But, it will not give you the quality of sleep you need to recover fully.”
How many hours should you sleep?
“Sleep need is very individual,” says Stanley. “Like height or shoe size, it is, to a great degree, genetically determined. Anywhere between four and 11 hours can be considered normal. However, on average, most of us are between seven and nine hours each night.”
A test to judge whether you are getting enough sleep is to see if you wake up feeling groggy, and whether your focus lasts throughout the day. That feeling of grogginess, called sleep inertia, can take up to two hours to snap out of, according to Stanley, and may be a sign that you’re waking up mid-cycle due a lack of, too much, or perhaps just not enough routine in your sleep patterns.
Sleep, like, food, water, even oxygen, may cause health risks when extended to an extreme. “After all, wakefulness in the correct amount is evolutionarily adaptive, as is sleep. Both sleep and wake provide synergistic and critical, though often different, survival advantages”, explains Walker. “In humans, the adaptive balance of wakefulness and sleep appears to be around sixteen hours of total wakefulness and around eight hours of total sleep, for an average adult.” he adds.
英國女影星柯德莉夏萍於電影珠光寶氣（1961年紐約）中看着躺在她背上的貓 (Photo by Mondadori Portfolio via Getty Images)
How can you get a better night’s sleep?
Try these simple tactics to get the optimum amount of sleep:
- Make sleep a priority: Block out at least eight hours per night.
- Train your body: Going to bed and waking up at the same time will regulate your body’s rhythms, resulting in a more sound sleep.
- Have a hot bath before bed: Walker recommends keeping your bedroom at around 20oC (68oF) to allow your body to drop its core temperature – a hot bath will help with this too.
- Consider your melatonin levels: Lights and screens – be they television, tablet or mobile – set the production of melatonin (the sleep hormone) back by up to three hours. A dark room, free of screens, will aid your sleep.
Watch your caffeine and alcohol intake: Both caffeine and alcohol are stimulants, so if you’re trying to regulate or improve your sleep, it’s best to cut back here. - Don’t stay in bed if you can’t sleep: If you are still awake 20 minutes after going to bed, get up and read a book in dim light – this helps keep your bed associated with being asleep only.
- Try a weighted blanket: Clinical studies that show that “grounding the body”, with a weighted blanket – try Sumo Sleep’s version – reduces cortisol levels and helps align the circadian rhythm of the body that prompts sleep.
Originally published on British Vogue.
Editor
Emma Strenner
