Regularly sleeping six hours or fewer per night during middle age may be associated with a greater risk of dementia, according to a new study.

Researchers say their findings cannot establish cause and effect, but suggest a link exists between sleep duration and dementia risk.

The study suggests there is a higher risk of dementia in those sleeping six or fewer hours per night at the age of 50 to 60.

There was also a 30% increased dementia risk in those with consistently short sleeping patterns from middle to older age (from 50 to 70 years), irrespective of cardiometabolic or mental health issues (known risk factors for dementia).

These findings suggest that short sleep duration in midlife is associated with an increased risk of late-onset dementia

Writing in Nature Communications, the authors say: “Here we report higher dementia risk associated with a sleep duration of six hours or less at age 50 and 60, compared with a normal (seven-hour) sleep duration, although this was imprecisely estimated for sleep duration at age 70.”

They add: “These findings suggest that short sleep duration in midlife is associated with an increased risk of late-onset dementia.”

The study indicates that sleep may be important for brain health in midlife, and future research may be able to establish whether improving sleep habits may help prevent dementia.

Nearly 10,000,000 new cases of dementia are reported worldwide every year.

A common symptom is altered sleep, but researchers say there is growing evidence to suggest sleep patterns before dementia onset may contribute to the disease.

While time spent sleeping is linked to dementia risk in older adults (65 years and older), it is unclear whether this association is also true for younger age groups.

Severine Sabia, from the University of Paris, and colleagues analysed survey data from UCL’s Whitehall II study that has examined the health of 7,959 British individuals since 1985.

Participants self-reported their sleep duration, and some wore watch accelerometers overnight to confirm this was an accurate estimate.

The authors write: “Whether sleep parameters also affect late-life dementia remains the subject of debate.

“While incipient dementia is known to affect sleep–wake cycles, the extent to which sleep duration over the adult life course is associated with late-onset dementia is unclear because most studies have not explicitly considered age at assessment of sleep duration or the length of follow-up.

“Our approach pays attention to both these aspects along with inclusion of a wide array of covariates to show that short sleep duration in midlife is associated with an increased risk of dementia.

“Public health messages to encourage good sleep hygiene may be particularly important for people at a higher risk of dementia.”

Dr Sara Imarisio, head of research at Alzheimer’s Research UK, said: “We know that the diseases that cause dementia start up to two decades before symptoms like memory loss start to show, so midlife is a crucial time for research into risk factors.

“In this study, sleep duration was largely measured through study volunteers self-reporting their sleep duration, and while this group of volunteers was not reflective of the UK population, it does offer insight into the relationship with sleep and dementia in mid to later life.

“This study cannot tease apart cause and effect and while it suggests that persistent lower sleep duration was linked with an increased risk of dementia, it did not find an association between longer than average sleep duration and dementia risk.

“While there is no sure-fire way to prevent dementia, there are things within our control that can reduce our risk.

“The best evidence suggests that not smoking, only drinking in moderation, staying mentally and physically active, eating a balanced diet, and keeping cholesterol and blood pressure levels in check can all help to keep our brains healthy as we age.”