Regularly going without a good night’s sleep once you hit middle age could increase your risk of developing dementia, according to data from a UK study that followed nearly 8000 people for 25 years.

The research published in academic journal Nature Communications shows people over 50 who said they consistently got six hours or less sleep a night were about 30 per cent more likely to develop dementia in old age.

This was regardless of whether they had other risk factors such as heart conditions, poor diet, poor mental health or smoking.

Researchers from the University of Paris analysed data from the UK’s Whitehall II longitudinal study, which recorded the health and lifestyles of thousands of British civil servants from 1985.

They say their research doesn’t prove that poor sleep causes dementia, because they cannot rule out that sleeping badly could be one of the very earliest symptoms of dementia.

But it adds to evidence that persistent poor sleep may be a contributing factor in whether you develop the brain disorder.

One theory for this is that toxins and proteins that build up in the brain are flushed out during sleep, as a clear liquid called cerebrospinal fluid moves through the brain.

Dementia affects around one in 14 people aged over 65, and about one in six people over 80.

The research follows a study earlier this week reported in the European Heart Journal highlighting the importance of sleep.

That study found that severely disrupted sleep could nearly double women’s risk of dying of heart disease.

The risk to men rose by about a quarter if they regularly had very poor sleep.