First world problems: we're not getting A's because we're not catching enough Z's.

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It’s hard to master math when you’re too tired to keep your eyes open in class. While nutrition and family income have previously been associated with academic performance, now quantity of sleep has also been shown to play a role, according to a Boston College analysis reported on by the BBC. The study, which draws on data culled from tests taken by more than 900,000 students in 50 countries, found that the U.S. has the greatest proportion of students whose academic performance, particularly in math and science, suffers due to poor sleep, with 73% of 9 and 10-year-olds and 80% of 13 and 14-year-olds affected. Those rates are significantly higher than the international average of 47% and 57%, respectively.

The top 5 countries where poor sleep hampers learning are:

United States New Zealand Saudi Arabia Kuwait Australia

The study found variations within countries too. For example, in the U.S., middle school students in Colorado are more sleep deprived than their cohorts in Massachusetts.

Countries where sleep has the least impact on learning are:

Kazakhstan Azerbaijan Slovakia Japan Malta

(MORE: Why Are We Depriving Our Teens of Sleep?)

The findings were part of a 2011 study that gauged education benchmarks around the world. In order to assess how sleep and nutrition affected these results, Boston College researchers sent questionnaires to teachers, students and parents about students’ sleep habits. Those responses were then compared with test performance. The results of the new comparison have not been published in a peer-reviewed journal.

“Sleep is a fundamental need for all children,” Chad Minnich of the TIMSS and PIRLS International Study Center at Boston College told the BBC. “Our data show that across countries internationally, on average, children who have more sleep achieve higher in maths, science and reading,” Minnich added.

The low level of Z’s in affluent countries like the U.S. and Saudi Arabia are attributed to students having cell phones and tablets at their finger tips — literally. The light from the screen, held close to the face, makes it harder to fall asleep. “Having a computer screen that is eight inches away from your face is going to expose you to a lot more light than watching a television on the opposite side of the room. It’s going to tell your brain to stay awake,” Dr. Karrie Fitzpatrick, a sleep researcher at Northwestern University in Illinois, told the BBC.

While the news is discouraging for U.S. parents, the problem can be fixed fairly easily. “As long you haven’t gone into extreme sleep deprivation, if you go back to seven to nine hours per night, as long as there has been no permanent damage, you can probably restore the functionality of accumulating, processing and being able to recall memories,” says Dr. Fitzpatrick.

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