Study suggests 7 hours of sleep is best

Both sleeping more or less than this number may impact health
03 May 2022

Interview with 

Dr Christelle Langley, University of Cambridge


clock surrounded by clouds and moon


We all know how good it feels to get a decent night's sleep, and now, a new research study published this week in Nature Ageing thinks it has found the sweet spot for the optimal number of hours individuals in mid-to-late lifeshould be getting. Dr Christelle Langley, one of the authors on this paper, from the University of Cambridge joins Julia Ravey to explain the findings…

Christelle - Our study showed that 7 hours of sleep was the optimal duration in a large cohort of middle to later aged individuals, for cognition, mental health and wellbeing. But it's not only the duration of sleep that it's important, but also the consistency of optimal sleep matters. Fluctuations in sleep duration over time were also associated with poorer cognitive and mental health outcomes. We identified some of the key brain regions also associated with sleep duration and these included the hippocampus, which is well known for its role in learning and memory, and also areas of frontal cortex, which are involved in the top down control of emotion.

Julia - Wow. So sleep is very important. I mean, I always think 'how do you study sleep?' Because you can't very well be standing over lots of people and watching them and monitoring them as they sleep. What methods did you employ to come to these conclusions?

Christelle - This particular study was a collaboration between researchers at the University of Cambridge and Fudan University. We used existing data from the UK biobank, which is a large scale database of approximately 500,000 individuals. This database includes questionnaires, measures of sleep duration, measures of cognition including things like processing speed, memory and executive function, and it also includes questionnaires of mental health symptoms, including depression and anxiety. We examined whether sleep duration was associated with any of these measures, and we specifically used something called nonlinear models to investigate these associations. Essentially this allowed us to determine the optimal duration of sleep where either more or less would have a negative impact on cognition and mental health.

Julia - So on average individuals who get less than 7 hours sleep a night, what relationships did you see there with these people?

Christelle - We did use these nonlinear models, which allowed us to specifically test how many hours of sleep cognition and mental health were best. We showed that both too little and too much sleep was associated with poor cognitive performance. The relationship may suggest that non-optimal sleep may be a risk factor for cognitive decline in aging and this is supported by reports where insufficient or excessive sleep was associated with an increased risk of developing dementia. We can't say for sure, why too little sleep has a negative impact on cognition, but it's possible that it may be due to the disruption of slow wave sleep, which has been shown to be important for memory consolidation and reduced sleep may also have a negative consequence on the clearance of toxins and this is also a really important component of sleep.

Julia - And very briefly, for some individuals, it may be the case that they just can't get to sleep and it's quite frustrating sometimes to hear "you must get 7 hours". Based on your results, have you got one tip to someone who is struggling to sleep?

Christelle - Some of the recent technologies suggest that using apps or sleeping diaries to monitor sleeping behavior is a really good idea.


Add a comment