Karen Weintraub, Special for USA TODAY
Children and young adults take longer to recover from a concussion if they've suffered a previous hit to the head within a year or repeated blows at any time, according to a new study.
Doctors had assumed it was bad for kids to get multiple knocks on the head, but the new study, from Boston Children's Hospital, is the first to confirm the connection and put a time frame on recovery.
The study found that kids and young adults, ages 11-22, who came to the emergency room with a repeat concussion - either within a year, or multiple times over a lifetime - took longer to recover than those with a first concussion. A single previous concussion more than a year earlier did not increase the risk for a longer recovery.
Most kids bounce back from concussions within a few weeks, but some take months, and doctors are trying to understand what makes the difference so they can better treat and protect them.
The new study, published Monday in the journal Pediatrics, suggests that the effects may last longer than previously thought - something coaches and parents should consider in deciding when kids should return to the athletic field, says Matthew Eisenberg, a study author and physician at Boston Children's. "This just adds another little weight to the risk side," when weighing benefits and risks, he says.
Patients without a prior concussion took 12 days on average to recover, while those with several previous concussions took 28 days. Recovery from a second concussion within a year took 35 days, the study found. About 60% had been injured playing sports.
It's not entirely clear whether the recovery is longer because the damage lingers unseen for a long time after a blow, or because someone who has had a previous concussion is more likely to be aware of symptoms.
Concussions can happen to anyone, Eisenberg says, but they are of particular concern in children, because doctors don't know how concussions affect the developing brain.
Research among professional football players and boxers suggests that the repeated blows can cause permanent damage, including an Alzheimer's-like condition and possibly an increased risk of suicide. Researchers don't know if there's any added risk for the typical amateur athlete.
"There may be a subgroup of kids, particularly those who play contact sports who are at risk over the course of their adolescence - those are the ones we worry about," says Eisenberg, also an instructor in pediatrics at Harvard Medical School.
A concussion is generally defined as any hit to the head that causes a change of consciousness or leaves the person feeling dazed, confused, forgetful or with a headache, nausea, dizziness or balance problems.
Another recent study in The Journal of Pediatrics found that concussions are more likely to happen during games than practice sessions. It's not clear whether that's because of the added pressure of playing competitively, or because parents and coaches are more likely to notice an injury during a game.
But the benefits of physical activity and teamwork vastly outweigh the risks of concussion, says Gerard Gioia, a concussion expert at Children's National Medical Center in Washington, D.C.
"Virtually all kids get better from these injuries - they really do," he says. "The question is how long it takes."