Noble Pettayil Babu

Too little or too much sleep’ more likely to cause cognitive problems in the long-term. Scientists at the University of Cambridge have found that the perfect dose of sleep is seven hours for people wanting to keep their minds healthy in middle age and beyond.

Sleep plays an important role in enabling cognitive function and maintaining good psychological health. It also helps keep the brain healthy by removing waste products. As we get older, we often see alterations in our sleep patterns, including difficulty falling asleep and staying asleep, and decreased quantity and quality of sleep. It is thought that these sleep disturbances may contribute to cognitive decline and psychiatric disorders in the ageing population.

In research published in Nature Aging, scientists from the UK and China examined data from nearly 500,000 adults aged 38-73 years from the UK Biobank. Participants were asked about their sleeping patterns, mental health and wellbeing, and took part in a series of cognitive tests. Brain imaging and genetic data were available for almost 40,000 of the study participants.

A possible reason for the link between insufficient sleep and cognitive decline may be the disruption of slow-wave, or deep, sleep, which has been shown to be important for memory consolidation. A lack of deep sleep could also prevent the brain from clearing toxins effectively.

Professor Barbara Sahakian from the Department of Psychiatry at the University of Cambridge, one of the study’s authors, said: “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.”

A disruption to slow-wave “deep” sleep may be one reason for the connection between reduced cognition and insufficient sleep. This is because deep sleep is closely associated with memory consolidation as well as the build-up of amyloid, an important protein which, when it misfolds, can create “tangles” in the brain typical of some forms of dementia.

A lack of sleep may also affect the brain’s ability to rid itself of toxins. Prof Jianfeng Feng, from Fudan University in Shanghai, said: “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”.