“Simply put, you need enough to make you refreshed and able to function effectively the next day.”  

Professor Morgan, Loughborough University's Sleep Research Centre 

Is six to nine hours the right amount for adults? 

How much sleep we need depends partly on our age and partly on our individual needs. The NHS advises: 

• Most adults need between six and nine hours of sleep each night. Some people can feel perfectly rested with a lower amount.
• Newborn babies can sleep for 16 hours a day, while school age children need an average of 10 hours.
• Most people over the age of 70 tend to be light sleepers and may need less than six hours a night. 

Six to nine hours sleep for adults roughly fits with a review of research findings published in 2013. This concluded: ‘Short and long sleep durations are behavioural risk factors for subsequent mortality and morbidity in adults. Habitual short sleep (sleeping ≤6 hours per night) is an independent predictor of all-cause mortality, cardiovascular events, metabolic dysfunction, obesity, and poor mental health. Habitual long sleep (sleeping >9 hours nightly) predicts premature mortality, cardiovascular disease, and cognitive impairment.‘ 

However, what is an ideal amount of sleep for an adult, within the 6–9 hour range suggested? Here the research findings sometimes differ. 

Is more sleep better? 

The Royal Society of Public Health commissioned Oxford University to produce a report on sleep, published in 2016. This concluded that adults aged 18–64 should be getting 7–9 hours of sleep per night (and those aged over 65 should be getting 7–8 hours per night). Less than this was said to increase the risk of physical and mental illness, including cancer, cardiovascular disease, stroke and depression.

In 2015 the National Sleep Foundation convened an 18-member multidisciplinary expert panel, to evaluate scientific literature concerning sleep duration recommendations. The panel agreed that, for healthy individuals with normal sleep, the appropriate sleep duration was 7 to 9 hours for working age adults, and 7 to 8 hours of sleep for older adults. This was the same verdict as the 2016 Oxford University study. 

Or when it comes to sleep, might less be worth more? 

Research from Cambridge University, published in 2015, suggests that sleeping over 8 hours per night is associated with an increased risk of Stroke.  

This matches with earlier research in the US, published in 2002, which found, ‘‘The best survival rates were found among those who slept 7 hours per night.” Although this is now quite an old study it did involve over a million people over a six year period, so was a sizeable piece of research. 

A 2013 study into human cognitive performance looked at the effect of sleep. It found cognitive performance was greater for users reporting larger amounts of sleep up to 7 hours per night, after which it began to decrease. 

What are the studies really telling us? 

First, the research cited so far suggests a relationship between the amount of sleep we get and how long we live. However, is this a cause and effect relationship? It may be, for instance, that when someone becomes unwell, they start to sleep more. In other words sleeping more might be a symptom of ill health rather than a cause. 

Second, we need research into other factors, like quality of life and health. ‘There are many reasons to continue to urge people to obtain adequate sleep,’ advises the National Sleep Foundation, which notes that bad moods, a higher risk of accidents and negative effects on the immune system are all associated with inadequate sleep. ‘Mortality is not the only important outcome measure.’ 

This is corroborated by News from Harvard Health, which comments, ‘ A good night's sleep is good for health. “Short sleepers” put on more pounds than people who sleep seven to eight hours a night. Subpar slumbering has been linked to diabetes, heart attacks, and even early death. When you stay awake for long stretches, it wreaks hormonal havoc; levels of the stress hormone cortisol go up, and your appetite gets out of whack.’ 

Third, we may need to consider the quality of sleep, not just the quantity. We know there are different stages of sleep, including periods of REM (rapid eye movement) sleep, which is when most dreaming occurs. As we get older the time we spend in REM sleep seems to reduce. Might the type of sleep we are getting matter? So far, this doesn’t seem to have been much researched. 

Other factors, like work patterns, can also affect our need for sleep. The UCLA Sleep Disorders Center explains shift work can be a particular problem. It means you are fighting your natural body clock, which is set for sleep while it is dark and being awake while it is light. The Center comments, ‘Some researchers think that it may take as long as three years to adjust to a shift work schedule. Others believe that you will never fully adjust to an unusual sleep/wake pattern.’  

Conclusions 

More research is probably needed. However it looks as if: 

• Seven to eight hours sleep a night seems a reasonable target for adults
• We need enough sleep to make us refreshed and able to function effectively the next day 

Reviewed by Laura Symes April 2016. Next review date February 2020.