Last month, the Journal of the American Dietetic Association published the most comprehensive review to date of why kids and teenagers should eat breakfast. The article surveyed the results of 47 research papers published since 1970 and reported triumphantly that breakfast-eating seems to "improve cognitive function related to memory, test grades, and school attendance." Kids who eat early in the day also tend to be better off in terms of overall nutrition and are possibly less likely to be obese. So, is this scientific vindication of what your mother always used to tell you—that breakfast-eating is crucial to academic success?
Not exactly. There is an alternate—and perhaps more compelling—explanation for why breakfast-eaters do relatively well in school while breakfast-skippers may have a tough time: The skippers are also the ones whose bodies rebel against early-morning activity. Their circadian clocks are telling them that it's still nighttime, or they're plain exhausted and need the extra zzz's. Taken together, the scientific literature on breakfast and sleep suggests that making sure kids get enough shut-eye will probably do more for them than dragging them out of bed to eat their Wheaties. Yet the authors of the new review article—like most nutrition researchers—overlook the literature on sleep, which seems to exist in a separate, academic bubble. That's too bad, because differences in kids' sleep patterns may underlie the questions about cognition and academic performance—as well as health effects like obesity—that the breakfast club is most interested in answering.
The case for circadian rhythms and sleep as key to performance has strong scientific grounding. Sleep researchers have shown that peoples' preferences for morning or evening activity—for being an early bird or a night owl—are partly genetic and can be apparent even early in life. The body's 24-hour cycles are mediated by a brain area called the suprachiasmatic nucleus, located in the hypothalamus. Small substitutions, or polymorphisms, in several circadian clock genes seem to cause variations within the SCN that may contribute to distinct sleep patterns and time-of-day preferences. Factors like family routine can play a role; still, some people just rise and shine more easily than others.
These tendencies can have a big impact on cognitive performance. People test significantly better at the time of day they identify as their best than they do at the time they say is their worst, especially in mental tasks involving memory. This is intriguing, since memory-related tests are also the ones that breakfast-eaters seem to excel at. Yet apparently no one has done a study on breakfast, cognitive performance, and time-of-day preference (or at least no one whom the reviewers in the Journal of the American Dietetic Association mention in their article). So, we don't know whether the kids who do worse on early-morning tests are struggling because they haven't eaten breakfast or because they aren't morning people.
Another sleep-related reason why some kids struggle in school is that as they hit puberty, their circadian rhythms tend to shift, pushing back their natural bedtime and making it harder for them to wake up early and think clearly in morning classes. Whatever time they finish their homework and get offline, most teenagers find it tough to fall asleep before 11 p.m. or so. When the alarm goes off at 6:30 the next morning, they are still likely to be in deep sleep, and their brains will protest fiercely against the intrusion. Whether a 12- or 14-year-old is groggy or bright-eyed in the morning, then—and whether or not she is hungry for breakfast—may reflect how far along in development she is. These findings may also help to explain why breakfast-skipping is more common in teens than in younger children.(Less is known about how many adults eat breakfast and whether doing so helps them.)
Of course, cognitive performance is also hindered by sheer exhaustion. And there's growing evidence to suggest that teens in particular are frequently sleep-deprived. Parents often think that children need less sleep as they grow up. The research, on the other hand, shows that adolescents still require a solid nine and a quarter hours of sleep a night—at least as much as their younger counterparts. But given their shifting circadian rhythms, budding social lives, and after-school demands, they average only seven and a half hours of sleep on weeknights, with roughly a quarter getting six and a half hours or less. No wonder some of them sleep till noon on Saturday and Sunday.
And no wonder they doze off in class. Studies have found that brief periods of micro-sleep intrude on the waking brains of people who are sleep-deprived, making them more or less oblivious to what is going on around them, even if their eyes are open. Mary Carskadon, a sleep expert at Brown University, has pointed out that the brain patterns of many teenagers look like those of narcoleptics. Not surprisingly, lack of sleep is associated with poorer school performance as well as moodiness. To combat these problems, a number of school districts across the country have begun to experiment with starting the school day an hour or so later. Data on one such program in Minnesota show an overall improvement in attendance, though the impact on grades is ambiguous.
Schools also cite academic as well as nutritional justifications for serving breakfast. The program has worthy anti-poverty roots, but there is no clear-cut agreement as to why eating breakfast should boost performance. The ADA Journal article summarizes some potential mechanisms: It's possible, for instance, that the increase in blood glucose that follows a meal benefits the brain, which relies on the sugar as a metabolic fuel. Yet studies have found no consistent link between higher glucose levels and higher test scores. Another possibility is that the main job of breakfast is to stave off rumbling stomachs, which may distract kids from learning. And, in fact, the clearest cognitive benefit of breakfast has been found among undernourished children. That doesn't tell us much, though, about the well-fed kids who say they don't eat breakfast because they aren't hungry. The breakfast club exhibits a number of other weaknesses. Some of its research does not control for socioeconomic status, leaving open the possibility that disparities in wealth, not breakfast-eating, underlie differences in performance. And the review does not address whether or not what kids ate first thing in the morning was healthful.
So, how have we gotten so fixated on breakfast as a key to good performance? Here's some historical speculation. The point, of course, is not that breakfast-eating is bad; from a nutritional perspective, it probably has real merit. But except in undernourished kids, it's not clear that eating breakfast makes you sharper in the morning. And whatever the meal's merits, it doesn't make a lot of sense for researchers who study it to ignore the evidence about sleep patterns and circadian rhythms that is probably confounding their results. As it happens, lack of sleep bears on at least two other areas that nutritional researchers are now exploring: the possible links between breakfast-skipping and obesity and childhood illnesses. (The ADA Journal includes another paper on the obesity front this month.) In both these areas, sleep matters: Sleeping less is clearly tied to being overweight, and exhaustion is associated with compromised immunity. It's past time for the breakfast club to wake up to the findings on sleep (and, in all fairness, for the sleep camp to pay more attention to the nutrition literature). In the meantime, you can deduce for yourself this Wheaties-busting wisdom: The best way to handle the cranky kid who doesn't want breakfast is to let her sleep.