For years, we've all been in pursuit of the ever-elusive eight hours of sleep. But now, more research suggests the ideal number might be closer to seven.

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For years, we've all been in pursuit of the ever-elusive eight hours of sleep. But now, more research suggests the ideal number might be closer to seven.

Researchers at the University of California San Diego tracked 1.1 million people over 6-years as part of a cancer study. They published their findings in 2002. People who reported sleeping 6.4 to 7.4 hours had the lowest mortality rates. They concluded: "Patients can be reassured that short sleep and insomnia seem associated with little risk. . . Slight risks associated with 8 or more hours of sleep and sleeping pill use need further study."

In the past 12 years, there have been a few studies to support the suggestion.

Dr. Kripke (who was also involved in the earlier study) recorded sleep activity of elderly women. Researchers measured sleep by monitoring wrist devices (considered more accurate than reporting sleep hours). A decade later, researchers found those who slept fewer than five hours or more than 6.5 have a higher mortality rate.

Last June, a study titled 'The largest human cognitive performance dataset reveals insights into the effects of lifestyle factors and aging' tracked how sleep changes performance. The study used Luminosity, a web-based cognitive training site.

The study used three tests: (1) Speed Match where users respond whether the current object matches the one previously shown, (2) Memory Matrix which users are shown a pattern of squares on a grid, and must recall which squares were present following a delay, and (3) Raindrops is a speeded arithmetic calculation task in which new arithmetic problems continuously appear at the top the screen inside of raindrops. Users need to answer the problems before the raindrops reach the bottom of the screen.

Researchers reported, "We found that cognitive performance in all three tasks was greater for users reporting larger amounts of sleep up to 7 h per night, after which it began to decrease."

Does that mean everything we've been told about getting as much sleep as possible is wrong? Maybe.

The CDC is helping to fund a panel of medical professionals and researchers to develop new sleep recommendations by 2015.

How much sleep do you get each night and what do you think the ideal number is?

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