Researchers at the San Diego School of Medicine found that women those who slept for between five and six-and-a-half hours a night had the longest survival rates.
While adults are advised to sleep for seven to nine hours every day to stay healthy, the researchers found that those who get slightly less than the recommended amount tend to outlive those who sleep much more.
The findings, they said, would help dismiss the long-held belief that people aren't getting enough sleep, the Daily Mail reported.
The scientists, who monitored 459 elderly women in San Diego for 14 years (since 1995) to try and establish a link between sleep and mortality, found that those who slept for between five and six-and-a-half hours daily had the longest survival rates.
In their first study they worked out peoples' sleeping habits using wrist activity monitors, which are able to tell whether a person is awake or asleep by how much they move and then count up the overall hours of sleep a night.
Last year the researchers tried to get back in touch with all the women 14 years later to find out whether they were still alive. They established that those who had more than six and a half hours sleep a night or less than five were far less likely to be alive today.
Professor Daniel Kripke, who led the study, said: "The surprise was that when sleep was measured objectively, the best survival was observed among women who slept 5 to 6.5 hours.
"Women who slept less than five hours a night or more than 6.5 hours were less likely to be alive at the 14-year follow-up."
Professor Kripke said their study should allay some people's fears that they're not getting enough sleep. He added: "This means that women who sleep as little as five to six-and-a-half hours have nothing to worry about since that amount of sleep is evidently consistent with excellent survival. That is actually about the average measured sleep duration for San Diego women."
Long term studies show that those who drop down to five hours or fewer face a 70 per cent extra risk of dying from all causes. The new study is published in journal Sleep.