Seven hours may be the ideal amount of time for people in middle and old age to sleep, newresearch suggests.

In a study from the University of Cambridge and China's Fudan University, 1_______ 500,000 British adults between the ages of 38 and 73 completed surveys about their sleep. Many also 2_______ cognitive(认知的)tests, and about a third completed a survey on their mental 3 _______ and well-being.

The results 4_______ that participants who said they slept an 5_______ of about seven hours aday did best in the cognitive tests, had the lowest symptoms(症状)of anxiety and depression,and had the highest feelings of well-being.

Brain scans done on almost 40,000 participants showed that the areas of the brain most affected by sleep included the memory center. However, Sahakian said the researchers are not yet sure why too much sleep could have a 6_______ effect, although one idea was that people might 7_______ longer in bed if they sleep poorly and wake up a lot.

Sahakian said that 8 _______ a good night's sleep is important for people of all ages, adding,“Ithink it is as important as doing 9_______.”

However, Russell Foster, a sleep expert at the University of Oxford who did not take 10 _______in the study, disagreed with the results, telling us that the ideal amount of sleep is different for everyone, and that "one size does not fit all."