Just one extra hour of sleep a day appears to lower the risk of developing calcium deposits in the arteries, a precursor to heart disease, U.S. researchers said on Tuesday.

    The finding adds to a growing list of health consequences — including weight gain, diabetes, high blood pressure — linked to getting too little sleep.

    "We found that people who on average slept longer were at reduced risk of developing new coronary artery calcifications over five years," said Diane Lauderdale of the University of Chicago Medical Center, whose study appears in the Journal of the American Medical Association.

    "It was surprisingly strong," Lauderdale said in a telephone interview.

    Calcium deposits in the coronary arteries are considered a precursor of future heart disease. "It's a very early marker of future risk," she said.

    Unlike other studies looking at the risks of getting too little sleep, which use people's own estimates of their sleep patterns, Lauderdale's team set out to measure actual sleep patterns.

    They fitted 495 people aged 35 to 47 with sophisticated wrist bands that tracked subtle body movements. Information from these recorders was fed into a computer program that was able to detect actual sleep patterns.

    The team used special computed tomography, or CT, scans to assess the buildup of calcium inside heart arteries, performing one scan at the start of the study and one five years later.

    After accounting for other differences such as age, gender, race, education, smoking and risk for sleep apnea, the team found sleep duration appeared to play a significant role in the development of coronary artery calcification.

    About 12 percent of the people in the study developed artery calcification during the five-year study period. Among those who had slept less than five hours a night, 27 percent had developed artery calcification.

    That dropped to 11 percent among those who slept five to seven hours, and to 6 percent among those who slept more than seven hours a night.

    Lauderdale said it is not clear why this difference occurred in people who slept less, but they had some theories. Because blood pressure tends to fall off during sleep, it could be that people who slept longer had lower blood pressure over a 24-hour period.

    Or, it could be related to reduced exposure to the stress hormone cortisol, which is decreased during sleep.

    Or it may be some unidentified process.

    "It's something of a mystery," Lauderdale said.

    Kathy Parker, a sleep researcher from the University of Rochester's School of Nursing in New York, said the study underscores the role sleep plays in health.

    "People think that sleep doesn't matter but clearly it does. Sleep deprivation is a public health problem and studies such as this show how increasing sleep duration can have tremendously positive effects," Parker, who was not involved in the research, said in a statement.

    Lauderdale said her findings should be confirmed by others, but said many studies point to the need for at least six hours of sleep a night.

    美國研究學(xué)者周二指出，每天多睡一個(gè)小時(shí)，可以降低動脈鈣化沉積的風(fēng)險(xiǎn)，而動脈鈣化沉積正是心臟病的一種先兆。

    研究還發(fā)現(xiàn)，一組正在不斷增長的健康問題與睡眠太少有關(guān)，包括體重增加、糖尿病和高血壓等。

    “我們發(fā)現(xiàn)，那些平均睡眠時(shí)間比較長的人群，五年內(nèi)發(fā)現(xiàn)新的冠狀動脈硬化的風(fēng)險(xiǎn)減低了。”美國芝加哥醫(yī)學(xué)中心的戴安娜·勞德代爾說，她的研究成果發(fā)表在美國醫(yī)學(xué)會雜志上。

    “它的效果非常明顯。”勞德代爾在一次電話采訪中說。

    冠狀動脈鈣化沉積被視為將來心臟病發(fā)作的先兆之一。“這是一種預(yù)示未來心臟病發(fā)作風(fēng)險(xiǎn)的早期表現(xiàn)。”她說。

    在針對睡眠過少帶來風(fēng)險(xiǎn)的研究當(dāng)中，其他研究者利用的是受訪者對自己睡眠模式的評估，而勞德代爾不同，她的研究團(tuán)隊(duì)使用了一種可以直接測量受訪者實(shí)際睡眠形式的方法。

    他們?yōu)?95名35歲至47歲的受訪者配備了先進(jìn)的手腕帶，可以追蹤記錄其細(xì)微的身體動作，記錄下來的信息被輸入一項(xiàng)計(jì)算機(jī)程序，從而發(fā)現(xiàn)其實(shí)際的睡眠模式。

    該研究小組采用了一種特殊的計(jì)算機(jī)斷層掃描或者CT技術(shù)來評估心臟動脈內(nèi)的鈣化沉積狀況，掃描共進(jìn)行兩次，一次在研究開始時(shí)，另一次在五年之后。

    在將其他諸如年齡、性別、種族、教育程度、吸煙及睡眠呼吸暫停風(fēng)險(xiǎn)等差異因素計(jì)入之后，研究團(tuán)隊(duì)發(fā)現(xiàn)睡眠時(shí)間長短在冠狀動脈硬化的形成過程中起到了非常重要的作用。

    在此項(xiàng)研究中，在五年內(nèi)約有12%的受訪者存在動脈硬化問題。每天睡眠不足五小時(shí)的受訪者中，有27%患有動脈硬化。

    而每天睡眠在5-7小時(shí)的人動脈硬化比例降到了11%，每天睡眠超過7小時(shí)者，有動脈硬化問題的只有6%。

    勞德代爾指出，目前造成這種差異的原因上不明確，但有其理論基礎(chǔ)。因?yàn)樵谒�眠期間，血壓會下降，因此那些睡眠時(shí)間較長的人在24小時(shí)內(nèi)的平均血壓較低。

    或者，它可能與壓力荷爾蒙皮質(zhì)醇在睡眠期間降低有關(guān)。

    或者是與其他一些未知原因的反應(yīng)有關(guān)。

    “這是一個(gè)謎。”勞德代爾說。

    美國紐約羅切斯特大學(xué)護(hù)理學(xué)院的睡眠研究員凱西·帕克表示，該項(xiàng)研究強(qiáng)調(diào)了睡眠在健康方面的作用。

    帕克，沒有參與過該項(xiàng)研究，而她在一份聲明中聲稱：“人們以為睡眠無關(guān)緊要，但實(shí)際上非常重要。睡眠剝奪已是一個(gè)公共健康問題，而像這樣的研究表明了睡眠時(shí)間的延長對于健康具有非常巨大的積極影響。”

    勞德代爾表示她的研究發(fā)現(xiàn)應(yīng)得到其他研究者的證實(shí)，不過許多其他研究指出，人們每天至少需要的睡眠時(shí)間為6個(gè)小時(shí)。