Sleeping in on Saturday after a few weeks of too little shuteye may feel refreshing, but it can give a false sense of security.

New research shows chronic sleep loss cannot be cured that easily. Scientists teased apart the effects of short- and long-term sleep loss and found that the chronically sleep-deprived may function normally soon after waking up,but experience steadily slower reaction times as the day wears on, even if they had tried to catch up the previous night.

It is work with important safety implications in an increasingly busy society, not just for shift-workers but for the roughly one in six Americans who regularly get six hours or less of sleep a night.

"We know that staying awake 24 hours in a row impairs performance to alevel comparable to a blood-alcohol content beyond the legal limit todrive," said lead researcher Dr. Daniel Cohen of Boston's Brigham andWomen's Hospital.

But when the chronically sleep-deprived pull an all-nighter, "the deterioration is increased tenfold," Cohen said.

The National Institutes of Health says adults need seven hours to ninehours of sleep for good health. Regularly getting too little increasesthe risk of health problems, including memory impairment and a weakenedimmune system. More immediately, too little sleep affects reactiontimes; sleepiness is to blame for car crashes and other accidents.

The new work shows how two different sleep drives impact the brain, oneduring the normal waking hours and the other over days and weeks ofsleep loss.

It has critically important ramifications for anyone who works "crazy hours" and thinks they are performing fine with a few hours of weeknight

sleep, said Shelby Freedman Harris, behavioral sleep-medicine directorat New York's Montefiore Medical Center, who was not involved with thenew research.

"Don't think you can just bank up your sleep on the weekend, because it doesn't work that way," Harris warned.

在一连几个星期睡眠不足的情况下，到了周六睡个懒觉可能会让你感到神清气爽，但这会给你一种错误的安全感。

最新研究表明，长期缺觉没那么容易补回来。科学家分别对短期和长期缺觉的影响进行了研究，发现长期缺觉的人在醒来后可能可以很快进入正常状态，但在当天之后，反应速度会逐渐变慢，即便他们试图补回前一夜缺的睡眠。

在如今日益繁忙的社会，这项研究具有重要的安全警示意义，不仅对于那些需要倒班的人来说如此，对于那些每晚睡眠不足六小时的六分之一美国人来说也一样。

该研究负责人、波士顿布莱根女子医院的丹尼尔？科恩博士说："我们知道，一连24小时不睡觉会影响你做各种事情的表现，这种影响相当于在饮酒过量时驾车。"

但如果长期缺觉的人彻夜不眠，"这种影响会增加十倍".

美国国立卫生研究院说，成年人每天需要七至九个小时的睡眠才可保持身体健康。长期缺觉会增加患病风险，包括对记忆力的损害和免疫能力下降。更直接的影响是，睡眠不足会影响反应速度，开车时打瞌睡是导致撞车等事故的主要原因。

这项新的研究揭示了两种不同的睡眠驱力是如何对大脑产生影响的，一种是在正常清醒的状态下，另一种是在连续几天或几个星期缺觉的情况下。

纽约蒙特费尔医疗中心的行为睡眠医学主任谢尔比？弗里德曼？哈里斯说，这项研究对于那些玩命工作，却还认为每天睡几个小时也能应付的人来说具有极其重要的警示作用。哈里斯没有参与这项新研究。

哈里斯警告说："不要以为周末睡个懒觉就能把睡眠补回来，因为根本不是那么回事。"