We spend on average 3,000 hours in dreamland each year – or in other words, a third of our life span between the duvet covers and the pillows – and for good reason. Sleep is linked to a range of cognitive and physiological processes in the body, and not getting enough (or sometimes even getting too much) can have unwanted health consequences.
As we grow older, we may also experience changes in our sleep patterns, and knowing just how much sleep is optimal for healthy functioning becomes important. Reporting in the Journal Nature Aging, scientists from Cambridge and Fudan University may have found an answer.
Examining data from UK BioBank, the researchers looked at 498,277 participants between 38 and 73 years old that completed surveys about their sleeping pattern and duration, mental health, and general wellbeing. From this group, 40,000 participants had brain imaging profiles and additional genetic data available for analysis.
The results of the study suggest that participants that had approximately 7 hours of sleep per day without major disruption in their day-to-day sleeping patterns for prolonged periods had better cognitive performance and improved mental health and general wellbeing in the long run.
Having less or more sleep seemed to be associated with impaired cognitive performance on tasks such as memory and problem-solving skills, and mental health in participants.
The authors also discovered a link between the amount of sleep and changes in the volume of key brain regions involved in memory, such as the hippocampus and other areas involved in cognitive processing in some participants. They speculate that changes in brain volume and other genetic mechanisms might underpin the underlying changes in cognition and mental health during those that had differential sleep duration.
“While we can’t say conclusively that too little or too much sleep causes cognitive problems, our analysis looking at individuals over a longer period of time appears to support this idea. But the reasons why older people have poorer sleep appear to be complex, influenced by a combination of our genetic makeup and the structure of our brains.” Professor Jianfeng Feng from Fudan University said in a statement.
The authors hint at a possible explanation for why insufficient sleep as we get older could lead to cognitive decline, explaining it might be due to a disruption of slow-wave sleep, which has previously been linked to dementia and memory difficulties. Although the current study doesn’t speculate why too much sleep might be a bad thing, previous studies have shown too much sleep could also lead to cognitive decline.
A certain strength of the current study is the large sample size that was used, and the results could therefore be considered robust. However, the authors do highlight some limitations. The surveys were self-reported, which may introduce some bias, and it only asked questions about total sleep duration in participants and did not look at other aspects such as sleep hygiene practices.
Future studies could certainly elaborate on these findings, but for now, we can confer that as we get older, 7 hours of snooze time every night seems to be optimal when it comes down to our napping practices.
“Getting a good night’s sleep is important at all stages of life, but particularly as we age. Finding ways to improve sleep for older people could be crucial to helping them maintain good mental health and wellbeing and avoiding cognitive decline, particularly for patients with psychiatric disorders and dementias.” Professor Barbara Sahakian from the Department of Psychiatry at the University of Cambridge concludes.