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Body clocks don't just spring ahead

This weekend the clock sprang forward an hour, three weeks earlier than the usual spring wake-up call. While it was a simple thing to move the clock hands or change the digital clock (don't ask us about the DVD player), bodies don't reset so quickly.

"At first it throws me out of whack -- everything isn't how it's supposed to be," said Caitlin Hunyadi, 21, a senior at Boston University who was already dreading her 8:30 a.m. sociological theory class before the change even happened. "It takes me about a week to get used to it."

Actually, it should take only a day for the body to adjust to one hour's difference, said Dr. Charles A. Czeisler, chief of sleep medicine at Brigham and Women's Hospital. But, like Hunyadi, most people take about a week to return to their regular sleeping cycles and general daily routine.

Part of reason for the longer time stretch is that people aren't getting as much sleep as they should. Most get less than seven hours instead of around 8.2 to 8.4, he said. So in the spring, when most people have to wake up an hour ahead of schedule, it takes even longer to play catch-up, sometimes with dangerous results.

"Studies have shown that the Monday after daylight saving time, car accidents increase 10 percent on the highways," Czeisler said. "You're taking a sleep-deprived nation and cutting another hour off the board, not simply shifting the circadian rhythm."

That circadian rhythm is a natural body clock of waking and sleeping, but it can be reset by light cues, particularly sunlight. When light through the eyes reaches the suprachiasmatic nucleus (called the SCN), set right above where the optic nerves cross, the brain receives the signal to stop producing melatonin, which makes people feel drowsy. With the time change, external cues like your alarm clock and the garbage truck will eventually help you adjust.

While 24-hour cycles are standard, most mammals take repeated naps throughout the day rather than the human "16-hour marathon," Czeisler said.

Over the years, the start time of that marathon changes. Starting as teenagers and stretching through the 20s, most people are "evening types" who stay up late and sleep late. As adults move into the 30s and 40s, their sleep regimes become less flexible. If a Saturday-night party goes until 4 a.m., they will still get up around their regular morning wake schedule.

As age progresses, that inner alarm clock starts earlier and earlier, often waking people before they want to get up. Although "early morning awakening" is often a complaint among seniors, it's a benefit when it comes to daylight saving time because they're already awake, Czeisler said.

The best way to adjust would have been to start shifting schedules before the Sunday clock did, but to do that, you would have had to know that in the first place. With the shift a few weeks early this year, many people have been caught unawares.

"I had no idea," David Seah, 39, a freelance graphic designer, who normally wakes up about 6:30 a.m., said last week. "It's usually a surprise to me until somebody tells me."

Seah said it takes a little while to get used to waking up early, but he tries to look on the bright side of getting up in the dark.

"It's kind of cool because then I see the sunrise and that's a special treat," said Seah. "Sometimes I see it because I've been up that late, but it's weird catching the beginning rather than the end."

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