Don't sleep on this study.
Middle-age and older people should sleep seven hours each night for ideal rest and recovery, according to a study published last week.
The research, published in Nature Aging, studied nearly 500,000 people ages 38-73.
"While we can't say conclusively that too little or too much sleep causes cognitive problems, our analysis looking at individuals over a longer period of time appears to support this idea," co-author Jianfeng Feng said in a statement.
Researchers found people who got exactly seven hours of sleep on a consistent basis saw better mental health, better memory, increased ability to pay attention and fewer symptoms of depression.
Previous studies have also suggested seven hours is the ideal amount of sleep.
The latest study was conducted using the U.K.'s Biobank program and completed by researchers from the U.K. and China. It relied on participants reporting their own nights of sleep.
While the negative effects of sleep deprivation have been extensively studied, the researchers were confused by the downside of extra sleep.
"We don't really understand why sleeping longer would be a problem," co-author Barbara Sahakian told the Guardian.