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.

    在一連幾個星期睡眠不足的情況下，到了周六睡個懶覺可能會讓你感到神清氣爽，但這會給你一種錯誤的安全感。

    最新研究表明，長期缺覺沒那么容易補回來。科學家分別對短期和長期缺覺的影響進行了研究，發現長期缺覺的人在醒來后可能可以很快進入正常狀態，但在當天之后，反應速度會逐漸變慢，即便他們試圖補回前一夜缺的睡眠。

    在如今日益繁忙的社會，這項研究具有重要的安全警示意義，不僅對于那些需要倒班的人來說如此，對于那些每晚睡眠不足六小時的六分之一美國人來說也一樣。

    該研究負責人、波士頓布萊根女子醫院的丹尼爾？科恩博士說："我們知道，一連24小時不睡覺會影響你做各種事情的表現，這種影響相當于在飲酒過量時駕車。"

    但如果長期缺覺的人徹夜不眠，"這種影響會增加十倍".

    美國國立衛生研究院說，成年人每天需要七至九個小時的睡眠才可保持身體健康。長期缺覺會增加患病風險，包括對記憶力的損害和免疫能力下降。更直接的影響是，睡眠不足會影響反應速度，開車時打瞌睡是導致撞車等事故的主要原因。

    這項新的研究揭示了兩種不同的睡眠驅力是如何對大腦產生影響的，一種是在正常清醒的狀態下，另一種是在連續幾天或幾個星期缺覺的情況下。

    紐約蒙特費爾醫療中心的行為睡眠醫學主任謝爾比？弗里德曼？哈里斯說，這項研究對于那些玩命工作，卻還認為每天睡幾個小時也能應付的人來說具有極其重要的警示作用。哈里斯沒有參與這項新研究。

    哈里斯警告說："不要以為周末睡個懶覺就能把睡眠補回來，因為根本不是那么回事。"