Humans fall into two camps when it comes to biological clockwork: early-to-bed, early-to-rise larks or late-night-loving owls who awaken long after the crack of dawn. As any parent knows, teenagers may take owlishness to extremes. But their sleeping in is not slacking off, says chronobiologist Till Roenneberg of the University of Munich in Germany: Biology is to blame.
Roenneberg and his colleagues surveyed the sleep habits of 25,000 Germans, aged 8 to 90, and found that as the teenage years wear on, the hour when kids go to bed and get up drifts later and later. It’s not that they’re sleeping more, Roenneberg says. Rather, their circadian clock is skewed. But not indefinitely: Around age 20, the pattern reverses. The clocks tick back, and young adults begin to go to sleep and wake up earlier and earlier. Eventually, their clocks coincide with those of older people.
The abrupt change, say researchers, may mark the biological end of adolescence. A difference between the timing in men (who switch at 20.9 years) and in women (at 19.5 years) points to a biological cause, perhaps a hormonal effect.
Because the circadian clock is calibrated by exposure to sunlight, Roenneberg suspects the many hours some kids spend holed up in their dark rooms could push the clocks even later—a pattern that may be more prevalent in industrialized societies. The researchers also discovered that rural residents, whose lifestyle puts them in daylight more, retire and rise an hour earlier than city dwellers. “I think this is only the tip of an iceberg that shows us the consequences of dim-light environments,” Roenneberg says.
—Kathy A. Svitil
Besides knocking years off your life and hardening your arteries, cigarette smoking may have another nasty downside: It could lower your IQ. And the earlier you begin smoking, the more likely that brain damage will occur. Psychiatrist Leslie Jacobsen of Yale University and her colleagues gave smoking and nonsmoking 14- to 18-year-olds a battery of cognitive impairment tests and found that smokers, whether in withdrawal or not, performed significantly worse. “The most profound differences were those in working memory, which, ironically, is the skill they need to depend on the most while learning new material,” says Jacobsen.
But what of previous tests showing that nicotine boosts memory, concentration, and general cognitive functioning? There are a number of studies with conflicting results, says Jacobsen, and those showing benefits were not conducted with adolescent brains, which are still in development and more vulnerable to neurotoxins in cigarettes. “Moreover, those studies have tended to use just isolated nicotine and not all the potentially damaging substances in cigarette smoke,” she says. “We don’t know which substance in tobacco smoke might be responsible, but at this point there is strong evidence that smoking is damaging young brains.” —Jocelyn Selim
Do school programs that promote abstinence prevent kids from having sex? Apparently not, says a Texas A&M University study that found 23 percent of ninth-graders had already had sex before being exposed to a federally funded abstinence program. By the tenth grade that percentage had jumped to 39 percent, a figure not significantly different from the national average of students who never received abstinence education.
This year the federal government will spend $131 million on abstinence-only programs that do not include instruction on contraception or preventing sexually transmitted diseases. “The question is exactly what the money is buying,” says health education professor David Wiley of Texas State University. Legally, what to teach kids about sex at school is frequently left to the discretion of local school boards, which often hire outside abstinence-only contractors to do the job. Because of overwhelmingly increased federal funding for abstinence-only courses, that is often what students are taught. “Given the number already having sex,” Wiley says, “it seems more Ozzie and Harriet than realistic that information on contraception as well as abstinence wouldn’t better serve these kids.”—J.S.