NEW ORLEANS -- A study of more than 2,500 retired NFL players found that those who had at least three concussions during their careers had triple the risk of clinical depression as those who had no concussions.
Those who recalled one or two concussions were 1½ times more likely to be diagnosed with depression, said Kevin Guskiewicz, research director of the University of North Carolina's Center for the Study of Retired Athletes.
"The findings of this study are not simply relevant to 50-, 55-year-old, 60-year-old retired athletes" but to those currently playing, said Guskiewicz, lead author of the study published Thursday in "Medicine & Science in Sports & Exercise," the journal of the American College of Sports Medicine.
Repeated concussions may be even more dangerous for children, said Dr. Gerry Gioia, director of the pediatric neuropsychology program and the Safe Concussion Outcome Recovery & Education program at Children's National Medical Center in Washington.
"Kids, generally speaking, do worse than adults with generalized injuries" like concussions, he said.
He also noted that many of the retired players were on the field before the NFL began a concussion management program in the mid-1990s and before studies sponsored by the NFL and NCAA prompted new helmet designs.
"It will be interesting to see in 40 years what happens to these current players who have better management," Gioia said.
Dr. Amparo Gutierrez, a child psychiatrist before becoming associate professor of clinical neurology at LSU Health Sciences Center in New Orleans, said the study's biggest problem is that it relies on athletes' memory, unverified by doctors' records. But she said its chance of accuracy is improved by its response rate: 2,552 of the 3,683 retired players who were sent surveys completed and returned them.
The study did not say when this was done; Gutierrez said he has been collecting data since about 2001.
Guskiewicz said 595 players remembered at least three concussions -- an incident in which a blow to the head caused a change in mental status and at least one additional symptom such as headache, nausea, vomiting, fatigue, blurred vision or concentration or memory problems.
He said 884 remembered one or two concussions and 1,513 at least one. About half said at least one knocked them out or left them unable to remember what had happened.
The 269 who reported that a doctor had later diagnosed them with depression included about 20 percent of those who reported at least three concussions, nearly 10 percent of those who had one or two concussions and almost 7 percent of those without concussions.
An earlier study at UNC found retired athletes' chronic pain may also contribute to depression. Guskiewicz said his study analyzed its potential effect and those of numerous other potential causes and factors, including arthritis, stroke, cancer, age and mild cognitive impairment -- a middle area between the changes of normal aging and more serious mental problems.
"We controlled for all these factors, and, after doing that, we still found this link between concussion history and a diagnosis of depression at some point in life," Guskiewicz said.
The Centers for Disease Control and Prevention has estimated that more than 300,000 athletes lose consciousness from concussions every year in the United States, and the total number of such concussions could be as high as 3.8 million.
Guskiewicz's study involved only those concussions suffered in the NFL. But players also reported concussions during high school and college.
"We have many retired players in our database who had three to four concussions in just their short five-, six-year career, who also two to three in college, who had one to two in high school," he said. "Add these together and it's a cumulative affect over a playing career."
NFL spokesman Greg Aiello said: "We think it's interesting. But it does not prove anything. And we want to know more. And that's why we are spending close to $2 million on a study of concussions on our retired players."
Guskiewicz coaches youth football and has sons aged 7, 9 and 10 who all play. He said worries that young players will accept the notion that concussions don't matter.
"Kids look up to the NFL players," he said. "They see players who sustain concussions. And it's just concerning."
The league is considering a whistle-blower program to keep team officials from pushing players to play too soon after concussions, and commissioner Roger Goodell has ordered all 32 teams to send their doctors and trainers to a meeting about concussions next month. Gutierrez will be speaking to that meeting, Aiello said.
Concussions among NFL players have made news in recent months. A forensic pathologist who studied Andre Waters' brain after he killed himself in November said it had been damaged by concussions.
The 34-year-old Johnson said his mental problems began in 2002, when he had two concussions in four days: the first during an exhibition game and the second after coach Bill Belichick pushed him to join full-contact practice.