A Nod to Zzzzinc

ADOLESCENTS

It's the dilemma of parents camped out on the living room sofa, awaiting their teenager's return from a late date: Why is the same kid who was falling asleep at nine a few years back suddenly able to stay out past midnight?

The answer may have less to do with adolescent rebellion than a biological change in teenage brains that alters sleep patterns. And a key contributor to those shifting sleep habits is that most alphabetically challenged of nutrients, zinc.

Like humans, rhesus monkeys also begin staying up later during puberty, researchers at the University of California find, But a diet low in zinc foils the sleep shift. The result is monkeys who are chronologically adolescent but whose sleep patterns resemble those of preteens, report Mari Golub, Ph.D., Eric Gershwin, M.D., and colleagues.

While their primate pals stay active for hours after nightfall, zinc-starved monkeys quickly become too pooped to pop. They head off to bed nearly 90 minutes earlier than their normal counterparts.

The study, reported to the Society for Neuroscience, is the first to implicate biology in the teen penchant for later bedtimes. "It's always been attributed to social factors—rebelling against rules, peer pressure, things like that," says Golub. Those factors may well play a role, but there are clearly physiological influences, too.

Beyond its effects on sleep, zinc is crucial for growth during pregnancy, childhood, and adolescence. While humans are unlikely to be as severely zinc deficient as the study monkeys, Golub says only a fifth of teenage girls get as much as they should. The best sources? Red meat, grains, and shellfish (oysters are a veritaable zincfest).

As for you parents on the sofa: Sorry, zinc doesn't seem to affect adult sleep patterns. If you want to stay up late, stick with java.

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