Scientists have found exactly how many hours of sleep we need as we age

A study finds that exactly seven hours of sleep is ideal while more or less sleep can lead to health issues.

A woman sleeps (photo credit: INGIMAGE)
A woman sleeps
(photo credit: INGIMAGE)

We spend an average of 3,000 hours sleeping each year, i.e.a third of our life and although it's a lot of time, it doesn’t happen by chance. Sleep is associated with a variety of cognitive and physiological processes in the body, and a deficiency in it can lead to unwanted health consequences like chronic diseases, obesity and heart disease.

As we grow older, we may also experience changes in our sleep patterns, and it’s important to know how much sleep is necessary for healthy functioning. So how many hours is it recommended to sleep each night to get the beneficial effect of sleep? Scientists from the University of Cambridge in the UK and Fudan University in Shanghai have found the answer.

Examining data from UK BioBank, the researchers examined 498,277 participants aged 38 to 73 years who completed surveys regarding their patterns and duration of sleep, mental health and general well-being. From this group, 40,000 participants had brain imaging profiles and additional genetic data was given to be analyzed.

The results of the study, published in the journal Nature Aging, suggest that participants who slept about seven hours a day without significant disruption in their daily sleep patterns for extended periods had better cognitive performance. Also, their mental health and general well-being improved over the long term while a bit less or some more sleep appeared to be associated with impaired cognitive performance in tasks such as memory and problem-solving skills, and mental health in participants.

Dementia connection

 Eenie the cat sleeping. (credit: ARIELLA MARSDEN)
Eenie the cat sleeping. (credit: ARIELLA MARSDEN)

The authors also found an association between the amount of sleep and changes in the volume of central brain regions involved in memory such as the hippocampus and other areas involved in cognitive processing in some participants. "While we can’t say unequivocally that too little or too much sleep causes cognitive problems, it seems that our analysis that looks at people over a longer period of time supports this idea, but it seems that the reasons that older people suffer from poorer sleep are complex and due to a combination of individual genetic makeup and brain structure,” said Professor Jianfeng Feng of Fudan University in a statement.

The authors suggest a possible explanation for why insufficient sleep as we age may lead to cognitive decline and explain that it may be due to a slow-motion sleep disorder that was previously associated with dementia and memory difficulties. Although current research doesn’t speculate why too much sleep may be a bad thing, previous studies showed that too much sleep can lead to cognitive decline.

The present study had a relatively large sample so the results can be considered strong. Yet the authors highlight some limitations: the respondents reported themselves, which may present some bias, and the researchers only asked questions about participants' total sleep duration and not other aspects such as sleep hygiene practices.

"A good night's sleep is important at all stages of life, but especially as we get older. Finding ways to improve sleep for older people can be essential to help them maintain mental health and well-being and avoid cognitive decline, especially for patients with psychiatric disorders and dementia," concludes Professor Barbara Sahakian from the Department of Psychiatry at Cambridge University.