Seven hours of sleep is optimal in middle and old age, say researchers

Seven hours is the ideal amount of sleep for people in their middle age and upwards, with too little or too much little sleep associated with poorer cognitive performance and mental health, say researchers from the University of Cambridge and Fudan University.

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 aging population.

In research published today 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.

By analysing these data, the team found that both insufficient and excessive sleep duration were associated with impaired cognitive performance, such as processing speed, visual attention, memory and problem-solving skills. Seven hours of sleep per night was the optimal amount of sleep for cognitive performance, but also for good mental health, with people experiencing more symptoms of anxiety and depression and worse overall wellbeing if they reported sleeping for longer or shorter durations.

The researchers say one possible reason for the association between insufficient sleep and cognitive decline may be due to the disruption of slow-wave -- 'deep' -- sleep. Disruption to this type of sleep has been shown to have a close link with memory consolidation as well as the build-up of amyloid -- a key protein which, when it misfolds, can cause 'tangles' in the brain characteristic of some forms of dementia. Additionally, lack of sleep may hamper the brain's ability to rid itself of toxins.

The team also found a link between the amount of sleep and differences in the structure of brain regions involved in cognitive processing and memory, again with greater changes associated with greater than or less than seven hours of sleep.

Having a consistent seven hours' sleep each night, without too much fluctuation in duration, was also important to cognitive performance and good mental health and wellbeing. Previous studies have also shown that interrupted sleep patterns are associated with increased inflammation, indicating a susceptibility to age-related diseases in older people.

Professor Jianfeng Feng from Fudan University in China 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. 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."

The researchers say the findings suggest that insufficient or excessive sleep duration may be a risk factor for cognitive decline in ageing. This is supported by previous studies that have reported a link between sleep duration and the risk of developing Alzheimer's disease and dementia, in which cognitive decline is a hallmark symptom.

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."

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Steps per day matter in middle age, but not as many as you may think

Walking at least 7,000 steps a day reduced middle-aged people's risk of premature death from all causes by 50% to 70%, compared to that of other middle-aged people who took fewer daily steps.

But walking more than 10,000 steps per day -- or walking faster -- did not further reduce the risk, notes lead author Amanda Paluch, a physical activity epidemiologist at the University of Massachusetts Amherst.

The findings, published in JAMA Network Open, highlight the evolving efforts to establish evidence-based guidelines for simple, accessible physical activity that benefits health and longevity, such as walking. The oft-advised 10,000 steps a day is not a scientifically established guideline but emerged as part of a decades-old marketing campaign for a Japanese pedometer, says Paluch, assistant professor of kinesiology in the School of Public Health and Health Sciences.

One question Paluch and colleagues wanted to begin to answer: How many steps per day do we need for health benefits? "That would be great to know for a public health message or for clinician-patient communication," she says.

The researchers mined data from the Coronary Artery Risk Development in Young Adults (CARDIA) study, which began in 1985 and is still ongoing. Some 2,100 participants between age 38 and 50 wore an accelerometer in 2005 or 2006. They were followed for nearly 11 years after that, and the resulting data were analyzed in 2020 and 2021.

The participants were separated into three comparison groups: low-step volume (under 7,000 per day), moderate (between 7,000-9,999) and high (more than 10,000).

"You see this gradual risk reduction in mortality as you get more steps," Paluch says. "There were substantial health benefits between 7,000 and 10,000 steps but we didn't see an additional benefit from going beyond 10,000 steps.

"For people at 4,000 steps, getting to 5,000 is meaningful," she adds. "And from 5,000 to 6,000 steps, there is an incremental risk reduction in all-cause mortality up to about 10,000 steps."

Several features make this study particularly interesting and informative. For one, it involved people in middle age, while most step studies have been focused on older adults. So the findings can begin to suggest ways to keep people healthier longer and to avoid premature death, as some of the participants experienced.

"Preventing those deaths before average life expectancy -- that is a big deal," Paluch says. "Showing that steps per day could be associated with premature mortality is a new contribution to the field."

The study also featured an equal number of men and women and Black and white participants. Death rates for people walking at least 7,000 steps per day were lowest among women and Blacks, compared to their more sedentary peers. But there was a limited sample of people who died, and Paluch cautions that researchers need to study larger diverse populations to gauge statistically significant sex and race differences.

Paluch is eager to continue researching the impact of steps per day on health and how walking may be beneficial in a variety of ways at different life stages.

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