Like most creatures on earth, humans come equipped with a circadian clock, a roughly 24-hour internal timer that keeps our sleep patterns in sync with our planet. At least until genetics, age and our personal habits get in the way. Even though the average adult needs eight hours of sleep per night, there are “short-sleepers,” who need far less, and morning people, who, research shows, often come from families of other morning people. Then there’s the rest of us, who rely on alarm clocks.
For those who fantasize about greeting the dawn, there is hope. Sleep experts say that with a little discipline (well, actually, a lot of discipline), most people can reset their circadian clocks. But it’s not as simple as forcing yourself to go to bed earlier (you can’t make a wide-awake brain sleep). It requires inducing a sort of jet lag without leaving your time zone. And sticking it out until your body clock resets itself. And then not resetting it again.
To start, move up your wake-up time by 20 minutes a day. If you regularly rise at 8 a.m., but really want to get moving at 6 a.m., set the alarm for 7：40 on Monday. The next day, set it for 7：20 and so on. Then, after you wake up, don’t linger in bed. Hit yourself with light. In theory, you’ll gradually get sleepy about 20 minutes earlier each night, and you can facilitate the transition by avoiding extra light exposure from computers or televisions as you near bedtime.
But recalibrating your inner clock requires more commitment than many people care to give. For some, it’s almost impossible. Very early risers and longtime night owls have a hard time ever changing. Night-shift workers also struggle because they don’t get the environmental and social cues that help adjust the circadian clock.
和地球上大多数生物一样，人类也有生物钟。这个内置计时器大概以24小时为周期，负责调节我们的睡眠模式，使之与地球的节律同步。至少在不受遗传、年龄或个人生活习惯影响的情况下是这样的。普通成年人每晚需要8小时睡眠，但也有“短睡眠者”，他们只需要睡很短的时间。还有自然就会早起的人。研究显示，这样的人，其父母先人往往也能自然早起。除此之外，其他的人要早起就得靠闹钟了。
想要早起迎接黎明，还是有希望的。睡眠专家指出，经过一点训练（嗯，实际上需要很多训练），大多数人能调整自己的生物钟。但这不止是强迫自己早点上床那么简单（大脑很兴奋的时候，也睡不着）。这种训练需要人为制造时差感，但不必为此穿越时区。坚持训练，直到体内的生物钟调整到位，然后保持新的节律。
首先，每天把起床时间提前20分钟。如果一般在早上8点起床，而你希望提前到6点，星期一就把闹钟定在7点40，星期二定在7点20，依此类推。其次，每天醒来后，不赖床，要让自己暴露在光线下。从理论上讲，每天晚上你会比前一天提前20分钟感到睡意。为了增强效果，临睡前应该避免电脑、电视等发出的亮光。
但调整生物钟要下定决心，很多人觉得困难，有些人则根本做不到。起得很早的人和长期熬夜的人都很难改变作息规律。夜班工人改变起来也很吃力，因为他们接收不到调整生物钟所需的环境信号和社会信号。
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