Your brain starts to eat itself if it hasn't had enough sleep, according to a new study.

Researchers studied lab mice, and found that 'clean-up' cells were more active in their brains when they were sleep-deprived.

The cells, known as astrocytes, act like mini Hoovers in the brain, sweeping up cells as the brain's connections become weak and break apart.

'We show for the first time that portions of synapses are literally eaten by astrocytes because of sleep loss,' lead author Michele Bellesi told New Scientist.

According to the research team at Italy's Marche Polytechnic University, the seemingly alarming process is actually a positive thing.

The cells, known as astrocytes, act like mini Hoovers in the brain, sweeping up cells as the brain's connections become weak and break apart, according to Italian researchers

'They [our synpases] are like old pieces of furniture,' Bellesi said. 'And so [they] probably need more attention and cleaning.'

But he added that sleep-deprived brains showed ominous signs of activity that leads to Alzheimer's.

In sleep-deprived mice, brain cells called microglials were more active.

'We already know that sustained microglial activation has been observed in Alzheimer's and other forms of neurodegeneration,' Michele said.

The news comes on the heels of research that showed having too little sleep could put people at risk from heart disease.

The study found that having less than six hours sleep a night was associated with a higher risk of death in people with metabolic syndrome – a combination of diabetes, high blood pressure and obesity

Researchers said the effect was particularly strong in those with elevated blood pressure or poor glucose metabolism.

People with a common cluster of risk factors for heart disease and diabetes were around twice as likely to die of heart disease or stroke as people without the same set of risk factors if they failed to get more than six hours of sleep, according to the study published in the Journal of the American Heart Association.

For those who got more sleep, the risk of death was more modest.

The study is the first to measure sleep duration in a laboratory rather than relying on patient reports, and the first to examine the impact of sleep duration on the risk of death in those with a common cluster of heart disease risk factors.

The researchers randomly selected 1,344 adults with an average age of 49 who agreed to spend one night in a sleep laboratory.

Based on their test results, 39.2 per cent of the participants were found to have at least three of the risk factors, that when clustered together are known as the metabolic syndrome.

For the study, the cluster included body mass index (BMI) higher than 30 - the standard definition of being obese, as well as elevated total cholesterol, blood pressure, fasting blood sugar and triglyceride levels.

During an average follow-up of 16.6 years, 22 per cent of the participants died.

Compared to people without the same cluster of risk factors, those with metabolic syndrome who clocked more than six hours of sleep time in the lab were about 1.49 times more likely to die of stroke during the follow-up period.

But those who slept less than six hours in the lab were about 2.1 times more likely to die of heart disease or stroke.