Middle-aged people who regularly sleep six hours or less a night more likely to get dementia

Middle-aged people who regularly sleep six or less hours per night are just under a third more likely to get dementia, compared to those who sleep seven hours a night, according to new research.

The study carried out by researchers in the UCL faculties of Population Health Sciences and Brain Sciences, Université de Paris, INSERM, and Accelting, did not find any significant link between sleeping for eight or more hours, and dementia risk.

Lead author Dr Séverine Sabia at UCL Epidemiology & Public Health and INSERM, said: “Sleep problems are known to occur in people with dementia, but it remains unclear whether sleep duration in midlife affects the risk of developing dementia at older ages. Here, by using a very long follow-up period, we have found that short duration sleep in midlife, assessed more than 25 years before mean age at dementia onset, is associated with dementia risk in late life.”

She added: “While we cannot confirm that not sleeping enough actually increases the risk of dementia, there are plenty of reasons why a good night’s sleep might be good for brain health. These findings confirm the importance of sleep hygiene for health.”

There has been growing evidence to suggest sleep patterns before dementia onset may contribute to the disease.

The researchers used data from 7,959 British adults who are part of the Whitehall II cohort study, based at UCL. They self-reported their sleep duration six times between 1985-1988 (age range: 35 to 55 years) and 2015-2016 (aged 63 to 86) enabling the researchers to gauge sleep duration at ages 50, 60, and 70.

Some participants also wore watch accelerometers over a full week, to get an objective measure of sleep duration. By the end of the study period in 2019, 521 of the participants had developed dementia.

Previous studies have seen an increase in dementia risk among those who sleep for longer than average, but results were inconsistent. Further studies including more individuals with long sleep will be needed to understand the role of sleep duration in dementia risk.

Senior author Dr Archana Singh-Manoux at UCL Epidemiology & Public Health and INSERM, said: “We know that sleep is important to our brain health, as it is involved in learning and memory, waste clearance from the brain, and the ability of our brain cells to remain healthy. A better understand of how sleep features might shape our risk of dementia is needed, as this might help researchers develop new ways to reduce the risk of dementia, or to delay its progression.”

The Whitehall II study is supported by the National Institute on Aging, NIH, Wellcome, the Medical Research Council, and the British Heart Foundation.

The study was published in Nature Communications.