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Here's one more reason to make sure teens get enough sleep in between 3am Snapchat breaks: A new study suggests that tired teens are more likely than their well-rested classmates to end up on the wrong side of the law. 

Teenagers' body clocks tend to be out of sync with their schedules, thanks to their biology and, to a lesser degree, their fondness for late-night screen time. Rather than blame the pre-adult set for keeping odd hours, parents, teachers and other people invested in teens' well-being and academic success are crusading to tailor school schedules to teenage circadian rhythms. The later school start times movement, for instance, is fighting to push back the school day. And a growing number of schools are letting students catch up on sleep during the day — naptime is the new study hall.

Research overwhelmingly supports these efforts. Compared to well-rested teens (a slim control group if there ever was one), sleep-deprived teens get lower grades and suffer from more depression and other mood disorders. Now, we can add "more likely to commit crimes" to that list of fun outcomes.

For the current study, researchers from the University of Pennsylvania and the University of York analyzed a 1970s study that measured sleepiness levels in 101 15-year-old boys from the UK. Additionally, researchers pulled criminal records from 1990 to which of the study participants had gone on to commit crimes by age 29. They found that teens who'd reported daytime fatigue were 4.5 times more likely to become scofflaws than other participants.

Social adversity, researchers wrote, leaves kids stressed out and, as a result, under-slept and drowsy the next day.

Researchers proposed a few different pathways to explain how yawning through pre-calc might lead to criminal activity down the road. Ultimately, they determined that the chain of events starts not with sleepiness but with social adversity experienced by teens who grow up in high-crime and/or low-income neighborhoods.

Adversity, researchers wrote, leaves kids stressed out and, as a result, under-slept and drowsy the next day. Additionally, previous studies have linked low socioeconomic status with poor sleep quality. Sleepiness reduces functioning in and between brain regions vital to executive function tasks including paying attention. Attention deficits predispose teens to academic failure and, in turn, occupational failure. Without a diploma or a decent job, formerly tired teens are primed to break bad. Thus ends the downward spiral from backpack to handcuffs. (Cue the dramatic music.)

Researchers looked at other factors that might play a role the sleepiness-crime link, including antisocial behavior, i.e., displaying hostility towards other people and acting without consideration for their welfare. Kids who say sorrynotsorry for driving drunk, bullying classmates or tormeting teachers would score high for antisociality. Antisocial Personality Disorders, e.g., sociopathy, are very common among criminals. 

Researchers acknowledged the possiblity that antisocial behavior lay at the root of tiredness. Why? Antisocial teens have a penchant for breaking rules, including rules about going to bed. But, their analysis didn't support that idea. Teens who were both sleepy and antisocial did emerge as far more likely than other kids to commit crimes. But the sleepiness-criminality link remained after researchers eliminated antisociality from the equation.

Lead study author Adrian Raine said via email that they were able to rule out the idea that antisociaity explains everything because "even when we take away any effect of adolescent antisocial behavior on slep problems, we still get a drowsiness-crime relationship later on."

The study has plenty of limitations, including the fact that participants were all male and that the proposed cause-and-effect relationship between sleepiness and criminality is only based on data from two points in participants' lives. But, the results emphasize how vulnerable teens are to the impact of sleep deprivation on their brain function and behavior. The study is also a reminder that social inequalities seep into children's lives, to help or hurt them, in many subtle ways. 

The next step, Raine said, is to see if sleep problems in childhood predict adult crime in a completely different, larger population.