High school rate has more than doubled.

• Position: Sports Concussions - Sports injuries

Concussion rates in U.S. high-school athletes more than doubled between 2005-12, according to a study in the American Journal of Sports Medicine using data on nine team sports. Overall, the rate increased from .23 to .51 concussions per 1,000 athlete exposures. An exposure is defined as one athlete participating in one competition or practice.

The increase might appear to sound an alarm about sports safety, but the researchers suspect the upward trend in reported concussions reflects increased awareness--especially since the rates went up the most after the 2008-09 academic year. Around that time, states began passing legislation promoting education about concussions and setting "return to play" guidelines for youth sports. Media coverage about head injuries in professional athletes also has increased over the last five to 10 years.

"It's scary to consider these numbers because, at first glance, it looks like sports are getting more dangerous and athletes are getting injured more often," says study author Joseph Rosenthal, a physician at Ohio's Wexner Medical Center. "This study is observational, so it doesn't offer any proof about why the rates are going up, but I think in reality it's showing that concussions that were occurring before are now being diagnosed more consistently, which is important."

A concussion is an injury to the brain that produces a transient loss of brain function with symptoms of dizziness, lightheadedness, confusion, headache...