老年人需要較少睡眠的真實原因
It's common for older people to say they have trouble sleeping.
老年人說自己睡眠不佳是很常見的事。There seem to be two main difficulties: falling asleep at the start of the night and then waking up too early in the morning – yet finding it impossible to get back to sleep.
看起來問題主要有兩方面：一是晚上入睡難，二是早晨醒的太早，而且無法重新入睡。In some cases, the discomfort caused by a medical condition exacerbates sleep difficulties, but many find that even without the disturbance of physical symptoms, sleep still eludes them for at least part of the night.
在一些情況下，某些疾病加劇了他們的睡眠障礙，但是很多人在沒有身體不適的情況下，晚上也無法得到充分睡眠。
In a new study from Russia, 130 people went to a laboratory one morning and then stayed there all day and overnight. Staff kept them awake for the entire time, regularly asking them to assess how sleepy they felt.
在俄羅斯開展的一項最新研究中，共有130人於早上前往實驗室，在那裏呆了整天整夜。研究人員讓他們時刻保持清醒，並定時讓他們評價自己的睏倦程度。
These feelings of sleepiness vary throughout the day and night and in sleep deprivation experiments such as this, they are taken to reflect processes related to the body clock such as changes in body temperature at different times of day and the release of the hormone melatonin in the evening.
白天和晚上的睡意各不相同。在這樣的睡眠剝奪實驗中，被試者會反映出與生物鐘相關的身體變化，比如白天不同的體溫變化和晚上的褪黑激素的分泌情況。Then all this data was analysed in relation to a sleep diary the people had kept for the previous week, in order to see how the pattern of sleepiness and slow brainwaves varied according to propensity to be morning or evening types.
然後，研究人員分析了所有這些數據，並與過去一週他們的睡眠日記對照，根據早起傾向者或晚睡傾向者的不同特點，分析睡意和較慢的腦電波的分佈情況。The slow-wave activity in the volunteers' brains was also measured several times during the day and night. They found that, once again, the older people felt sleepy at different times from the younger people and had different timings of slow-wave activity in the brain.
研究人員還在白天和夜晚測量了志願者較慢的腦電波。他們再次發現，老年人的睡意分佈時間與年輕人不同，他們較慢的腦電波的出現時間也與年輕人不一樣。The study's author, Arcady Putilov, suggests that two mechanisms might be responsible for the decrease in sleep time. He believes that in middle age the processes underlying the oscillations of slow-wave sleep weaken, making it harder to stay asleep, and on top of that, in older age the stronger circadian rhythms weaken because changes in body temperature and the release of the hormone melatonin weaken.
該研究的作者阿卡狄·普提洛夫認爲，有兩套機制導致睡眠時間減少。人到中年，潛在的慢波睡眠減弱，讓人很難保持睡着狀態。而到老年，由於體溫的變化和褪黑激素的減少，較強的生物鐘節奏也會減弱。
