Seven hours of sleep may help keep your brain sharp

Researchers at the University College London found that getting too much or too little sleep can prematurely age a person`s brain by up to seven years.

They found that middle-aged adults whose sleep decreased to less than six hours a night over a five-year period scored lower in reasoning and vocabulary tests, while those who slept for over eight hours also showed signs of cognitive decline, the Daily Telegraph reported.

The researchers also found that women who had maintained seven hours of sleep per night performed best in cognitive tests as did men who slept between six and eight hours.

The findings suggested that regularly sleeping for seven hours during the night can help to reduce the cognitive decline that occurs as we grow older, they said and called for better public health advice about the importance of getting the right amount of sleep.

Dr Jane Ferrie, who led the research, said the decline in brain function suffered by people who got too much or too little sleep was equivalent to them having aged between four and seven years.

She said: "Sleep duration generally decreases with age and so does cognitive function, so we wanted to see if there was a relationship with that change in sleep.

"It was surprising that when people have longer durations of sleep, they had a lower cognitive function scores in all of the tests apart from memory.

"We think this could be to do with fragmentation of sleep which means although people are in bed for a long time, they are not necessarily having enough quality sleep.

"We calculated these changes in sleep are producing a cognitive deficit that is equivalent to a person having aged by between four and seven years."

For their study, the researchers used data from a long term public health survey known as the Whitehall II study.

Using data from questionnaires and cognitive tests completed by 5,431 participants, Dr Ferrie and her colleagues were able to assess how changes in sleep duration over a five-year period related to changes in cognitive scores.

The participants, who were aged between 35 and 55 years old, were asked to carry out six cognitive tests that examined reasoning, vocabulary, fluency and memory.

It was found that 25 per cent of the women and 18 per cent of the men taking part had decreased the amount of sleep they got each night while 7.4 per cent of the women and 8.6 percent of the men had increased the amount of sleep they got.

The results showed that those having less than six hours of sleep a night and those who sleep for more than eight hours had lower test scores for reasoning a.nd vocabulary.