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Tuesday 18th June 2019

Seven hours' sleep boosts memory

17th July 2012

A recent re-evaluation of data gathered from nurses in the United States shows that seven hours' sleep a night may be the optimum amount for women.

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Women who typically sleep no more or less than seven hours were shown to be at a reduced risk of dementia, and to have better functioning memories even during middle age.

By contrast, researchers at the Brigham and Women's Hospital in Boston found that women who slept five hours or less on average per day had lower scores on standard memory tests than those who slept seven hours.

Sleeping more than seven hours did not improve scores, however.

On the contrary, women who slept for nine or more hours per night also had lower memory scores than the group that slept for seven hours.

According to Brigham and Women's researcher Elizabeth Devore, who presented the study to the Alzheimer's Association International Conference in Vancouver, women who got too little or too much sleep had the memories of women about two years their senior.

She said that this held true for middle-aged women as much as for much older women.

The findings come after a recent study by the US Centers for Disease Control and Prevention (CDC), which found that more than 40 million US workers get less than six hours of sleep a night.

According to Devore, there is growing evidence to suggest that getting more or less than seven hours a day is linked to an increased risk of heart disease and type 2 diabetes.

She said her research team had hypothesised that sleep duration might influence memory, based on evidence that both heart disease and diabetes had been linked to an increased probability of memory problems.

Devore's team looked at data for more than 15,000 participants in the Nurses' Health Study, who had answered questions about how many hours they slept a night both in 1986 at ages ranging from 40 to 65, and in 2000, when they were aged 54 to 79.

The women were given a series of memory tests between 1995 and 2000, when all the participants were over 70, with follow-up tests every other year for the six years after the initial test.

The team found that the key factor that hampered memory was any change in sleep duration, rather than its absolute length. Women whose sleep patterns had changed by two or more hours from middle age to their senior years performed worse on memory tests than those whose sleep duration had remained constant.

According to Dean M. Hartley, director of science initiatives at the Alzheimer's Association, the study doesn't show cause and effect, however.

But researchers at Beth Israel Deaconess Medical Center have also found that a good night's sleep triggers changes in the brain that help to improve memory.

Sleep researchers recommend that people maintain a regular bed and waking schedule, including on weekends, and establishing a regular, relaxing routine around bedtime. They say people should avoid caffeinated beverages or chocolate before bed, and choose a comfortable mattress and pillows.

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