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Former National Football League (NFL) players who experienced concussion symptoms during their playing careers performed worse on cognitive tests later in life, cross-sectional data showed.

Retrospectively reported concussion symptoms were associated with worse performance on a battery of tests that assessed episodic memory, sustained attention, processing speed, and vocabulary nearly 30 years later, reported Laura Germine, PhD, of McLean Hospital and Harvard Medical School in Boston, and co-authors.

After adjusting for age, cognitive performance was correlated with football concussion symptoms (r_p -0.19, 95% CI -0.09 to -0.29, P<0.001) but not with diagnosed concussions, years of professional play, or age of first football exposure, the researchers wrote in .

The results emphasize the importance of tracking concussion symptoms in research, not just diagnosed concussions, Germine and colleagues noted. They also shed light on how professional football careers might affect cognitive aging.

"It is well established that in the hours and days after a concussion, people experience some cognitive impairment. However, when you look decades out, the data on the long-term impact have been mixed," Germine said in a statement.

"These new findings from the largest study of its kind show that professional football players can still experience cognitive difficulties associated with head injuries decades after they have retired from the sport," she noted.

The study evaluated 353 former NFL players with a mean age of 54 who completed both an online cognitive test battery and a survey about demographic information, health conditions, and past football exposure including recollected concussion symptoms playing pro ball, diagnosed concussions, years of professional play, and age of first football exposure.

Recollected concussion symptoms were measured by asking the players how frequently they experienced headaches, nausea, dizziness, loss of consciousness, memory problems, disorientation, confusion, seizure, visual problems, or feeling unsteady on their feet after a head hit during play or practice.

Cognitive testing occurred an average of 29 years after the final season of professional play and included an hour-long assessment on (a tool in 2005) to measure processing speed, visual-spatial and working memory, and aspects of short- and long-term memory and vocabulary.

A comparison sample of 5,086 male nonplayers also completed one or more cognitive tests.

Relationships between recollected football concussion symptoms and cognitive performance remained after adjusting for race, education, and playing position, but were largely attenuated after adjusting for reported anxiety and depression symptoms. "One possibility is that poorer cognitive performance, anxiety, and depression are all downstream effects of football injuries that produce concussion symptoms," Germine and co-authors suggested.

Age-adjusted cognitive performance was generally worse for former players than nonplayers. While younger former players outperformed nonplayers on some tests, older retired players were more likely to have worse cognitive scores than their counterparts, notably on two tests of processing speed.

There are several possible explanations for this, the researchers suggested.

"One possibility is that football exposure accelerates age-related declines in processing speed, producing cognitive disadvantages for former players relative to nonplayers at older ages, despite former players' similar or better performance at younger ages," Germine and colleagues wrote.

"A second possibility is that improved head injury prevention and management over time (e.g., by incorporating head impact sensor technology) has lessened the impact of football exposure on cognitive performance, sparing younger former players from processing speed disadvantages displayed by older former players," they pointed out.

An important study limitation is the lack of cognitive performance data before concussion symptoms emerged, Germine and co-authors acknowledged. More studies are needed to track cognitive changes in former pro sports players as they age, they noted.

"Future investigations of the long-term outcomes of contact sports exposure should include measures of sports-related concussion symptoms, which were more sensitive to objective cognitive performance than other football exposure measures, including self-reported diagnosed concussions," they wrote.

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