Sleep plays a fundamental role in enabling cognitive functioning and maintaining good mental health. Moreover, it helps keep the brain healthy by removing toxins. As we age, we often see alterations in our sleep patterns, such as increased difficulty of falling and staying asleep, together with decreased quantity and quality. Such disturbances often contribute to cognitive decline and psychiatric disorders in the elderly.
A new study led by the University of Cambridge in the UK and Fudan University in China has found that seven hours is an ideal amount of sleep for people in their middle age or older, with too little or too much sleep associated with poorer cognitive performance and mental health.
The researchers analyzed data from almost 500,000 adults aged 38-73 from the UK Biobank, who were asked questions about their sleeping patterns and mental health and wellbeing, and also took part in a series of cognitive tests. In addition, brain imaging and genetic data were available for nearly 40,000 of the participants.
The data analysis reveled that both insufficient and excessive sleep were associated with impaired cognitive functioning, including poorer visual attention, processing speed, and memory and problem-solving skills. Seven hours of sleep per night appeared to be an optimal amount for smooth cognitive performance and good mental health. People who reported sleeping for shorter or longer durations experienced more symptoms of depression and anxiety and worse overall wellbeing.
“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,” said study co-author Jianfeng Feng, an expert in Computational Biology and Data Science at Fudan University. “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.”
According to Dr. Feng and his colleagues, one possible reason for the association between insufficient sleep and cognitive decline may be due to the disruption of slow-wave, or “deep” sleep, which is known to lead to deficiencies in memory consolidation and the build-up of amyloid, an important protein which protects against dementia. Moreover, sleep disturbances are associated with increased inflammation and can hamper the brain’s ability to get rid of toxins.
“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 dementia,” concluded study co-author Barbara Sahakian, a psychiatrist at Cambridge.
The study is published in the journal Nature Aging.