Children until their midteens need more than eight hours of sleep a night, according to new guidelines for healthy sleep released by a health ministry study group.

The optimum number of hours of shuteye drops off as people age, decreasing to about seven hours at 25, about 6½ hours at 45, and about six hours at 65, according to the guidelines put together by 13 experts.

They note that sleep requirements vary by individual and less is generally needed as the hours of daylight lengthen. Still, they advise: “Try to get as much sleep as you need to avoid becoming sleepy during the daytime.”

They also note that sleeping longer than needed does not necessarily improve health.

The guidelines reflect new findings since they were introduced 11 years ago, such as the difference in sleep requirements according to age. They have been boiled down to 12 succinct pieces of advice that are intended to promote healthy sleep, the lack of which not only harms physical and mental health but also leads to accidents, according to Hiroyuki Noda, an official in the ministry’s health services bureau.

“We hope the guidelines give people the opportunity to take a fresh look at their sleep,” he said. “We also hope to urge companies to learn more about the importance of sleep so they will try to allow their workers to get enough sleep.”

The revised guidelines expand on the seven points in the 2003 edition, and feature specific findings to support individual recommendations, Noda said.

They advise against drinking alcohol before bed, a habit found to be more prevalent in men than women. Although it may promote drowsiness, once its effects wear off sleep becomes shallower, leading to the feeling of not having had enough rest upon waking.

The authors note that using cellphones in bed to make calls, read emails or play games should be avoided.

The guidelines debunk the idea that sleeping in on weekends to catch up on sleep lost during the week is effective, and call for getting the right amount of sleep each day.

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