How much sleep is enough? If you get less sleep than the ideal amount but you feel fine, could you be damaging your health anyway? Are we getting less than we used to? Recent research provides some surprising answers.
Adults typically need seven to nine hours of sleep each night to feel fully rested and function at their best. However, Americans are getting less sleep than they did in the past. A 2005 National Sleep Foundation poll found that Americans averaged 6.9 hours of sleep per night, which represents a drop of about two hours per night since the 19th century, one hour per night over the past 50 years, and about 15 to 25 minutes per night just since 2001.
Unfortunately, we are not very good at perceiving the detrimental effects of sleep deprivation. Researchers at the University of Pennsylvania restricted volunteers to less than six hours in bed per night for two weeks. The volunteers thought they were functioning relatively normally. However, formal testing showed that their cognitive abilities and reaction times progressively declined during the two weeks. By the end of the two-week test, they were as impaired as subjects who had been awake continuously for 48 hours.
Moreover, cognitive and mood problems may not be the only consequences of too little sleep. Researchers at the University of Chicago have shown that too little sleep changes the body's secretion of some hormones. The changes promote appetite, reduce the sensation of feeling full after a meal, and alter the body's response to sugar intake—changes that can promote weight gain and increase the risk of developing diabetes.
A study by Susan Redline and colleagues at Case Western Reserve University School of Medicine showed an inverse correlation between sleep duration and obesity in high-school-age students. The shorter the sleep, the higher the likelihood of being overweight, with those getting six to seven hours of sleep more than two and a half times as likely to be overweight as those getting more than eight hours.
睡眠不足帶給你的不僅僅是肥胖
美國(guó)《新聞周刊》撰文：多長(zhǎng)時(shí)間的睡眠時(shí)充足的？如果你的睡眠時(shí)間比理想的睡眠時(shí)間少，但你感覺正常，這是否仍會(huì)損害你的健康？我們的睡眠時(shí)間比過去少了嗎？最近的研究提供了一些令人吃驚的答案。
成年人通常每晚睡7到9個(gè)小時(shí)才能感到恢復(fù)徹底、狀態(tài)良好。然而，美國(guó)人的睡眠時(shí)間與過去相比越來越少。全國(guó)睡眠基金會(huì)在2005年的一次調(diào)查中發(fā)現(xiàn)，美國(guó)人平均睡眠時(shí)間為每晚6.9個(gè)小時(shí)，與19世紀(jì)相比，每晚減少約2小時(shí)，與50年前相比，每晚減少1小時(shí)，甚至與2001年相比也減少了約15至25分鐘。
遺憾的是，我們沒有很好地意識(shí)到睡眠不足的不良影響。賓夕法尼亞大學(xué)的研究人員要求志愿者在兩周時(shí)間內(nèi)每晚睡眠時(shí)間少于6小時(shí)。盡管這些志愿者在兩周后認(rèn)為他們的身體運(yùn)轉(zhuǎn)相對(duì)正常，然而，測(cè)試表明，兩周時(shí)間里，他們的認(rèn)知能力和反應(yīng)時(shí)間逐漸下降。到測(cè)試結(jié)束時(shí)，他們健康受損程度與那些48小時(shí)不睡覺的實(shí)驗(yàn)對(duì)象是一樣的。
不僅如此，睡眠過少的后果可能不只是認(rèn)知能力和情緒問題。芝加哥大學(xué)的研究人員已經(jīng)證明，睡眠過少能夠改變體內(nèi)某些激素的分泌。這些變化會(huì)促進(jìn)食欲，削弱對(duì)寶飽食的感覺，并改變身體對(duì)糖類攝入量的反應(yīng)，導(dǎo)致體重增加，增加患糖尿病的風(fēng)險(xiǎn)。
由凱斯-西部保留地大學(xué)醫(yī)學(xué)院的蘇珊-雷德蘭及其同事進(jìn)行的一項(xiàng)研究顯示，高中生的睡眠時(shí)間與肥胖程度呈反比。睡眠時(shí)間越短，超重的可能性就越大，睡眠時(shí)間為6到7個(gè)小時(shí)的學(xué)生身體超重的可能性事睡眠超過8小時(shí)的那些學(xué)生的2.5倍以上。
好消息是，充足的睡眠可以抵消這些影響。研究發(fā)現(xiàn)，讓實(shí)驗(yàn)對(duì)象連續(xù)兩天睡10個(gè)小時(shí)可以把激素水平恢復(fù)到正常，饑餓感和食欲水平下降近25%。
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