It’s daylight science time again

/ Source: contributor

It’s that time of year, when crocuses bloom, the lawn starts to need mowing, and most Americans lose an hour’s sleep setting their clocks ahead. (Remember? Spring forward, fall back.) So here are answers to your questions about the time switch — and about sleep.

Most Americans move their clocks ahead for daylight-saving time in the wee hours of the second Sunday in March. The day of the big switch used to be the first Sunday of April, but in 2005, Congress revised the rule as an energy-saving measure.

What's the rationale behind the switchover? As the year progresses toward the June solstice, the Northern Hemisphere gets longer periods of sunlight. Timekeepers came up with daylight-saving time — or summer time, as it’s known in other parts of the world — to 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 idea is that having the extra evening sunlight will cut down on the demand for lighting, and hence cut down on electricity consumption — and that few people will miss having it a little darker at, say, 6 o'clock in the morning. At least that's how the theory goes.

Not everybody goes along with the plan, as folks in places like Hawaii and most of Arizona know quite well. Each state or country comes up with its own schedule for the switch: Most European countries don't switch to summer time until the last weekend in March. And yes, some countries in the Southern Hemisphere are moving their clocks back an hour at this time of year.

If you’re in the “spring forward” mode, don’t lose any sleep over the hour you’re losing. Aside from leaving you a bit groggy, it won’t have much effect on your health. But Dr. Rosalind Cartwright, sleep expert at Rush Medical Center in Chicago, says that if you lose too much sleep, even a couple of hours for just two or three days, your immune system suffers, and you’re more susceptible to colds and viral infections.

She also explains that if you get to sleep too late, or up too early, your body will make sure it gets the deep sleep it needs for rest. What you lose is the light sleep during which you dream, which is important for mood. Which explains why you might feel groggy and grumpy after we “spring forward” to daylight-saving time.

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?

David Ropeik is a longtime science journalist and expert on risk communication. This article is adapted from the archives of “How and Why,” Ropeik’s column about scientific puzzlers, and was first published in March 2000. It has been adapted by NBC News for changing circumstances.