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Fall back ... into bed: It's time to reset your biological clock

If you've been falling behind on sleep, this is the weekend to fall back into bed for an extra hour — and take advantage of the transition from daylight saving time to standard time.
Clock conservator Eric Wilson makes adjustments to The Rittenhouse Clock in the Westphal Picture Gallery at Drexel University in Philadelphia. The clock, built in 1773 by astronomer David Ritenhouse, has 16 sets of chimes and plays 10 tunes.Chris Gardner / AP
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If you've been falling behind on sleep, this is the weekend to fall back into bed for an extra hour — and take advantage of the transition from daylight saving time to standard time.

The time change is part of a longstanding tradition, in which most Americans push their clocks ahead an hour in the spring ("spring forward") and turn them back an hour in autumn ("fall back"). The change officially takes place at 2 a.m. daylight saving time on Sunday, Nov. 6 (which instantly becomes 1 a.m. standard time).

A few years ago, lawmakers shifted the schedule slightly, setting the changeover for the first Sunday of November rather than the last Sunday of October. The goal was to extend the energy savings that are thought to result from daylight saving time.

The idea behind daylight saving time — or summer time, as it's known in other parts of the world — is to use the extended daylight hours during the warmest part of the year to best advantage. Timekeepers shift some of that extra sun time from the early morning (when timekeepers need their shut-eye) to the evening (when they play softball).

The shift reduces the need for lighting during the evening, and that's why daylight saving time is considered an energy-saver — that is, as long as there is morning sunlight to spare. Now that dawn is coming later and later, the daylight-saving advantage has largely dissipated

With the clocks turned back, it will be lighter (or at least less dark) in the morning, but darkness will fall earlier in the evening.

Not everybody goes along with the daylight-saving plan. Arizona and Hawaii, for example, stay on standard time all year round. Each state or country comes up with its own schedule for the switch, and that schedule may be subject to change.

Around the world, Canada and the members of the European Union operate similar summer-time shifts. Most European countries made the shift to standard time last weekend, so in that sense America is just now catching up. And yes, some countries in the Southern Hemisphere move their clocks forward an hour at this time of year, in time for the coming summer there.

If you're in a fall-back time zone, you'll want to savor that extra hour of shut-eye: A major study released by the National Center for Health Statistics indicated that sleep deprivation was linked to all sorts of health problems, including smoking and obesity.

Here are more questions and answers about the science of sleep:

When we wake up, why do we have crust in our eyes? - S.S.
“Eye crusts” are the leftover protein and fat from tears that have dried up. Tears have three components:

  • Salty water, which comes from the tear gland behind the upper outer corner of our eye.
  • Protein, secreted by the conjuctiva, which is the clear film that covers the eye.
  • And fat, which comes from ducts in the eyelids.

Tears do lots of jobs. They clean the eye. They fill in tiny imperfections in the surface of the cornea, which needs to be perfectly smooth for maximal vision. They also deliver nutrients to the cornea, which has to be clear to let light through to the iris, and therefore has no blood vessels to deliver a “food supply.” And of course tears flow at times of emotion, when the tear glands power up and produce more salt water.

At night, with our eyes closed and protected, we don’t display emotion, and with our eyes closed we don’t get dirt in our eyes. So we don’t make tears. Small amounts of the mixture already on the surface of the eye seep out, but without a fresh supply of liquid from the tear gland, the fat and protein dry up.

Why does your breath smell so bad when you wake up? - S.B. and A.B.
This one ought to get you to brush before you go to bed. That smell is ... bacteria gas. Gross, but accurate. There are lots of bacteria in our mouth all the time, feeding on the tiny leftover bits of what we’ve eaten. Ever hear of plaque, the stuff all those toothpaste ads promise to get rid of? Plaque is nothing more than organized colonies of bacteria chowing down on food bits on your teeth.

When we’re awake, some plaque is removed when we chew, talk, drink, even when we breathe. But overnight, when those disturbances in the mouth stop, it’s party time for the bacterial colonies on your teeth, and they multiply like crazy. Their waste products are acids, which cause cavities, and gases, which cause that rude blast of morning breath.

Why do we snore? - S.D.
To bug the person sleeping next to us, of course.

Actually, there are several causes of snoring. All of them have something to do with restriction of the upper airway.

  • Kids with swollen tonsils or adenoid glands snore.
  • People sleeping on their back snore because the tissues in the neck are pressing down on the windpipe.
  • Overweight people snore for pretty much the same reason, or because some of their fat is stored in tissues in the neck.
  • People with colds snore because they have swollen sinus tissues in their throat.
  • Drinking alcohol causes snoring by relaxing the muscles in the throat, which restricts the size of the airway.
  • We snore more as we age because of the loss of elasticity in neck tissues, which sag in on the windpipe.
  • People with misshapen jaws, larger-than-normal tongues, or on relaxant medications, all are more prone to snore.

So if you try to sleep next to an overweight elderly drunk with a misshapen jaw and a cold who’s taking muscle relaxants ... bring industrial-strength earplugs.

Why is yawning contagious? - P.H.
If you don’t think YAWNING is contagious, see if you YAWN by the time you’re done reading this explanation of YAWNING.

First, let’s dispel a myth. You don’t yawn to take in extra oxygen. “That’s been rejected in lab tests,” says YAWN expert Robert Provine, professor of psychology at the University of Maryland’s Baltimore County campus. He had test subjects breathe air with extra oxygen. For others, he reduced the oxygen intake by giving them air high in carbon dioxide. Neither caused more or less YAWNING.


Provine says “we YAWN when we’re changing states of activity. Going from sleep to wakefulness, like YAWNING in the morning. Or wakefulness to sleep.” (He says we YAWN more in the morning when we wake up, by the way.)

“Concert pianists will YAWN before going out to an important performance. Olympic athletes YAWN before the big event. Embryos begin YAWNING eleven weeks after conception,” Provine notes. He says YAWNING is somehow connected to changing levels of body activity, changes from one state to another, like inactive to active or vice versa, but nobody understands just what the connection is.

“It probably helps stir up the blood and brain chemistry to facilitate those transitions from one level of activity to another.”

Why? “YAWNING is ancient and autonomic,” Provine says. “Maybe it’s to get everyone in the tribe to synchronize their states of activity, to increase the success of the tribe if everyone’s working together. We really don’t know.”


YAWNING is highly contagious, he says. Every vertebrate species YAWNS. Fish YAWN. Birds YAWN. Alligators YAWN. But Provine says it’s apparently only contagious in humans.

Provine has made test subjects YAWN by showing them a YAWNING face. Interestingly, if he shows them just the YAWNING mouth, it doesn’t trigger the YAWNING. If he covers the mouth, and shows them just the nose and eyes of the YAWNING face, it does. He’s made subjects YAWN by talking about YAWNING, or asking the test subjects to think about YAWNING, or by having them read about YAWNING.

Yawning yet?

Alan Boyle is's science editor. David Ropeik is a risk communication consultant who provided information for this report in 2000.