It's the time of the year when high schoolers, particularly boys who put on football pads, are getting another round of warnings and tests for the consequences of concussions.
High school athletes sustain an estimated 140,000 to 300,000 concussions a year, with football players making up about half of the injuries.
But two recent studies suggest that while sports may be the leading cause of concussions, they're not the only sources of bumps, blows and jolts to the still-maturing brains of older teens, and they may be more common than has been thought.
Adolescent boys who are hurt in just two physical fights suffer a loss in intelligence quotient roughly equal to missing an entire year of school, a study published this week by Florida State University found. Girls experience a similar loss of IQ after only a single fight-related injury.
About 4 percent of high school students are injured in a fight each year, said Kevin Beaver, a professor of criminology and social justice, and doctoral student Joseph Schwartz, who published their study in the Journal of Adolescent Health.
The results were based on data from health surveys done in 1994 and 2002 that involved 20,000 middle- and high school students who were tracked into adulthood through further surveys.
The findings are particularly significant since many teens with concussions report having difficulty concentrating and focusing on schoolwork, among other symptoms. Decreases in IQ are linked to lower educational achievement and occupational performance, mental disorders, behavioral problems, even longevity.
Each fighting-related injury resulted in an average loss of 1.62 IQ points for boys, while girls lost an average of 3.02 points. Earlier studies have shown missing a single year of school is equivalent to a loss of about 2 IQ points.
More severe consequences for girls hurt in fights may be because males have increased physical ability to absorb trauma. A number of other studies focused on sports concussions have shown that girls may be more susceptible to the injury, and many take longer to recover.
The researchers noted that the surveys on fighting did not spell out what parts of the body were hurt, and suggested that the effect on IQ would likely be greater if only injuries to the head could have been studied.
Of course, sports and fights are not the only reasons for head trauma in teens. There are car crashes, injuries from daredevil stunts and accidents of all kinds.
A Canadian study published last month in the Journal of the American Medical Association found that one in five students ages 11 to 20 reported having a traumatic brain injury that knocked them out for five minutes or required them to be hospitalized overnight.
Most concussion studies have indicated that less than 10 percent of the injuries result in a loss of consciousness for any period of time.
Researchers at the Center for Addiction and Mental Health and St. Michael's Hospital in Toronto said the proportion of injuries was much higher than previously thought. It was the first large study of such injuries based on surveys, rather than hospital records. It used data from a survey of 9,000 public-school students across Ontario.
Although not all the students were athletes, the study showed that 47 percent of the injuries among girls occurred during sports versus 64 percent among boys.
Brain injuries were more common among students who reported having poor grades, drinking alcohol or smoking marijuana at least 10 times in the past year, the researchers noted.
Other research has suggested there are links among brain injury, substance abuse and mental health problems in teens, but the exact nature of the relationships -- including whether one problem contributes to another -- remains unclear.
The Centers for Disease Control and Prevention says 15 to 20 percent of patients with mild traumatic brain injury have symptoms such as dizziness, headache, concentration difficulty and mood swings that may last for days or weeks, but the new studies expand that list of long-term symptoms.
(Contact Scripps health and science writer Lee Bowman at BowmanL@shns.com. Distributed by Scripps Howard News Service, www.shns.com.)