American researchers found that older women who slept for seven hours a night had far better concentration and memories than those who slept for nine hours. Those who got less than five hours were also found to suffer, the 'Daily Mail' reported.
Scientists believe that those who restrict themselves to seven hours a night can prevent their brain from ageing by an extra two years, compared with those who get too much sleep or not enough.
Earlier research has shown that having more than seven hours of sleep a night can lead to weight gain and increase the risk of heart problems and diabetes. However, the new study is one of the first to link it to concentration problems.
The research, presented at the Alzheimer's Association International Conference in Vancouver, Canada, looked at 15,000 women in their seventies over five years.
All the participants underwent regular tests to check their memory, concentration and attention span. Those who usually slept for seven hours performed far better than those who got less than five hours, or more than nine.
"Our findings support the notion that extreme sleep durations and changes in sleep duration over time may contribute to cognitive decline and early Alzheimer's changes in older adults," lead researcher Elizabeth Devore of Brigham and Women's Hospital, Boston, was quoted as saying by the paper.
"The public health implications of these findings could be substantial, as they might lead to the eventual identification of sleep-based strategies for reducing risk of cognitive impairment and Alzheimer's," she added.
"A good night's sleep is one of life's pleasures but, once again, this robust research suggests that the quality and duration of sleep are also linked to our cognitive health," a spokesman for the Alzheimer's Society said.
"We're not saying you shouldn't enjoy the occasional lie-in, but good-quality sleep, eating a balanced diet, maintaining a healthy weight and exercising regularly can all make a difference in reducing your risk," he said.
