Interactive: Sleep science

By contributor
updated 3/6/2015 7:44:02 PM ET 2015-03-07T00:44:02

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.

© 2013  Reprints

Explainer: 10 spring flings with science

  • Spring, the season of fertility and frivolous flings, is a bounty for science as well. Science fests ranging from the World Science Festival in New York to thousands of fairs at local elementary schools, bring people together to celebrate the systematic search for knowledge — and have fun. Here's a scene from 2008's Great Moonbuggy Race in Huntsville, Alabama. Students assemble human-powered vehicles and then drive them over a mock lunar landscape replete with craters, lava ridges and sandy soils. Click the "Next" arrow above to learn about nine more spring flings with science.

    — By John Roach, contributor

  • Climate change brings earlier spring

    Ron Edmonds  /  AP file

    Judging by the tilt of Earth's axis, spring officially arrives in the Northern Hemisphere on March 20. But judging by biological clocks — when plants bloom, critters wake and birds sing — spring is arriving days to weeks earlier than it did just a few decades ago. For example, the famous cherry trees in Washington bloom about five days earlier than they did 30 years ago, scientists say. The reason? Climate change, of course.

  • Songbirds rush home in the spring

    Elizabeth Gow
    Wood thrushes, like this male shown with its electronic backpack, breed in eastern North America where passersby can hear the songbirds' melodic "Ee-oh-lay."

    Songbirds are in a much greater rush to migrate back to North America each spring from their South American wintering grounds than previously thought, according to scientists who outfitted critters such as the wood thrush shown here with tiny electronic backpacks. The gadgets recorded the birds' whereabouts for an entire migration cycle. Overall, the birds flew much quicker than expected, covering an average of 311 miles per day, compared with previous estimates of 93 miles per day. The biggest surprise was how quickly the birds returned to North America. Their trip was two to six times more rapid than their flight south. One bird, for example, flew to Brazil in 43 days, but returned in just 13 days. The quick flight may be related to a race to secure the best real estate for nesting.

  • Batten down the hatches for tornadoes

    During springtime, moist air replaces the cold and dry stuff of winter. But this seasonal transition can turn deadly when the warm air gets trapped under a stable layer of cold and dry air. If the surface heats up rapidly, or an influx of cold air rushes in, the warm air will rise and condense, forming clouds and thunderstorms. And if the winds are just so, the rising air will spin around a funnel and spawn a tornado that sweeps across the land, blowing apart everything in its path. This image shows a tornado funnel cloud approaching Atkins, Ark.

  • Pollution blunts scent of spring

    Image: Aerial view of Nyirangongo
    Getty Images

    Scientists say the sweet smell of spring given off by flowers in bloom is being blunted by pollutants from power plants and automobiles. Scent molecules produced by flowers quickly bond with pollutants such as ozone, which destroys the floral aroma. As a result, floral smells that wafted up to 4,000 feet in the wind from their source in the 1800s today travel less than 1,000 feet. The loss could be impacting pollinators such as bees, which rely partly on the sweet smells to locate nectar-laden flowers.

  • Easter: Where science (almost) meets religion

    Stringer/russia  /  Reuters
    The full moon stands over an Orthodox church in the village of Miadel, some 200 km (124.3 miles) north of Minsk March 20, 2008. Picture taken March 20, 2008. REUTERS/Vladimir Nikolsky (BELARUS)

    Easter — the Christian celebration of the day Jesus rose from the dead — is a movable feast. In other words, it is not fixed to a specific day of the Gregorian calendar but rather is pegged to the first full moon that occurs after the vernal, or spring, equinox. That's why Easter Sunday, a favorite spring holiday, occurs anywhere between March 22 and April 25. One point of contention is the church's fixing of the equinox to March 21 even though, astronomically speaking, spring officially starts no later than March 20, at European longitudes, between the years 2008 and 2101. As a result, astronomers would set Easter on March 28 in the year 2038, following the March 21 full moon, but the church sets that year's Easter on April 25 instead.

  • Spring means flood season in the lowlands

    Skiers and other winter sports enthusiasts know spring as the time of year when snow turns slushy and sloppy. All that meltwater combined with spring rains brings a different threat to residents of the Midwest: spring floods. A potent combo of abundant snowmelt and torrential rains proved disastrous throughout the region in 2008, when swollen rivers topped their banks and breached levees. The floods swept over towns such as Poplar Bluff, Mo., shown here.

  • Spring's fertility brings on the allergies

    Jim Sulley/wirepix  /  BW

    Spring is the season of fertility. Birds lay eggs. Rabbits do what rabbits do best. And trees, flowers and grasses bud, blossom and bloom, sending out pollen in hopes of attracting a mate. That particular harbinger of spring can drive us crazy with sneezes, sniffles and sleepless nights of the unenviable kind. That's because pollen can cause an allergic reaction. The body goes on the attack with a vengeance by producing so-called histamines — chemicals that cause the telltale sneezes, sniffles, watery eyes and everything else that seems like a bad cold, but without the fever, aches and pains.

  • Periodical cicadas emerge en masse

    James Appleby - University Of Il  /  AP file

    Just about every year, somewhere, millions of bugs with beady red eyes emerge en masse after 13- or 17-year stints underground where they sucked sap from tree roots. The mass emergence kicks off the final month of the periodical cicadas' life. The nymphs transform into adults, create a cacophonous ruckus searching for a mate, reproduce and die. And since their groups, known as broods, are so large, they prove a feast for critters great and small. Squirrels, birds, dogs, cats and even some humans consider them a protein-rich snack.

  • Time for bikinis and poor male decisions

    Joe Raedle  /  Getty Images file

    The sight of scantily clad women, according to rigorous scientific research, causes men to behave poorly, especially when it comes to financial decisions. In one set of experiments, for example, men who watched videos of bikini-clad women running through a park settled for less money in a negotiation than men who watched videos of men running through a landscape. Since spring time - and spring break - is the start of bikini season, men might want to be aware of the toll the bikini factor can have on their bank account.

Video: Daylight-saving time explained


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