A lack of shut-eye may not just leave you feeling groggy—it could seriously injure your brain. A new study of mice has found 25% of brain cells died off after prolonged sleep loss, meant to duplicate night shifts or long hours at the office—the first evidence of its kind and a scary find if it applies to humans. "We now have evidence that sleep loss can lead to irreversible injury," a researcher told the BBC, noting that when the mice lost a little sleep, they were protected by an energizing protein, but brain cells began to die off when sleep loss became a habit. "This suggests to us that we are going to have to look very carefully in humans."
If you don't get the recommended six to eight hours of sleep per night but substitute extra hours of snores later to catch up—like on weekends—that may not make up the difference either, researchers say, as the damage may already be done, CNN notes. While more research is needed—the group plans to study the brains of shift workers after death to look for nerve damage—there may also be a silver lining to look forward to: The team notes its research may eventually lead to medicines that help people deal with irregular sleep patterns caused by odd work hours. (Read more sleep stories.)