Sleep balance clue to Alzheimer’s

Researchers in the US studied sleep duration in more than 15,000 women aged 70 and older.

Those who slept for five hours or less a night performed less well in mental tests than those who slept for seven hours.

But spending too long in bed was not good for the brain either. Nine hours or more of sleep also led to reduced mental performance.

Sleeping less or more than seven hours had an effect equivalent to ageing by two years.

The women, participants in the Nurses Health Study, had their mental functioning assessed every other year for six years from the age of 70 onwards.

Average sleep duration was recorded twice, when the women were aged 40 to 65, and again at 54 to 79.

Women who changed the amount of time they slept by two hours or more from mid to later life suffered more mental decline than those whose sleep pattern stayed the same.

This effect was seen irrespective of initial sleep duration.

Sleep time also appeared to alter on a molecular biomarker of Alzheimer’s, suggesting that sleeping too little or too much might increase the risk of the disease.

Study leader Elizabeth Devore, from Brigham and Women’s Hospital in Boston, said: “Our findings support the notion that extreme sleep durations and changes in sleep duration over time may contribute to cognitive decline.”