High school and college students who get concussions may struggle more with academics than their peers who get other types of sports injuries, a small U.S. study suggests.

Researchers surveyed 70 students who received emergency treatment for concussions and 108 teens and young adults treated for other injuries.

With a concussion, students took an average of 5.4 days to return to school, compared with 2.8 days for other injuries.

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One week after getting hurt, 42 percent of the students with concussions received academic help such as tutoring or extra time for tests, compared with 25 percent with other injuries. One month afterwards, 31 percent of the concussion group got help, as did 24 percent of the other students.

"After a concussion, there is an energy crisis in the brain; the brain needs more energy to heal than it has available," said lead study author Erin Wasserman of the University of North Carolina at Chapel Hill.

"Because of this, individuals experience symptoms like headache and dizziness, they have trouble sleeping, they may experience depression, and they often have trouble concentrating and remembering things," Wasserman, who completed the study at the University of Rochester, said by email.

"All of these symptoms are known to cause problems in school," Wasserman added.

To assess how concussions impact schoolwork, Wasserman and colleagues surveyed student athletes treated at three emergency departments in the Rochester, New York, area from September 2013 to January 2015.

They excluded students who went to the emergency department more than 24 hours after the injury or who were hurt badly enough to require a hospital admission.

For the comparison group without concussions, researchers only included athletes with isolated injuries to the extremities, such as an arm broken in one place. Concussed students were excluded if brain scans showed what's known as acute intracranial lesions, or badly damaged tissue.

Researchers asked about symptoms and school performance one week and one month after injuries. Questions touched on things like their concentration skills, ability to do well on tests or quizzes, and symptoms like headaches and dizziness. Scores ranged from 0 to 174 with higher scores indicating worse academic difficulties.

At one week, 83 percent of the concussed students reported impairments in at least one area that they didn't experience before the injury, as did 60 percent of students with extremity injuries, researchers report in the American Journal of Public Health.

Also at one week, concussed students had academic dysfunction scores 15 points higher on average than their peers with other injuries at 63 and 48, respectively. After one month, though, their scores were similar: 42 with concussions and 40 with other injuries.

One limitation of the study is that 24 percent of concussed students hadn't returned to school within a week of their injury and were excluded from the analysis. That may mean only the less-impaired students were included and for others impairment after concussion could be worse than observed in the study.

With concussions, students may also have vision problems or difficulties with eye movements that impact school performance, said Anthony Kontos, research director of the sports medicine concussion program at the University of Pittsburgh Medical Center.

"Some students may experience difficulty shifting from near to far - like from a textbook to a chalkboard - following concussion," Kontos, who wasn't involved in the study, said by email.

With the potential for vision and concentration issues as well as symptoms like headaches and dizziness to complicate schoolwork, doctors advise students to take frequent breaks and try to stop work before symptoms get bad, said Dr. John Leddy medical director of the concussion management clinic at the University at Buffalo.

"We don't know for sure what the cause of difficulty with concentration and memory in school is but a common report is that of cognitive intolerance; that is, students cannot do their work for sustained periods of time before becoming very fatigued and thus unable to process new information," Leddy, who wasn't involved in the study, said by email.

"Academic problems likely reflect an issue of cognitive intolerance due to an inefficient brain after concussion," Leddy added.