Seven hours sleep is the ideal amount for staying sharp as we age, new research suggests. A study of almost 500,000 people aged between 38 and 73 found too little or too much was linked with worse cognitive performance and mental health, including anxiety and depression. One of the scientists who tok part in the research, Prof Barbara Sahakian from Cambridge University’s department of psychiatry, said: “For every hour that you moved away from seven hours you got worse.” A good night’s sleep was important at all ages but particularly as people aged. “I think it is as important as getting exercise.”