Sports-related head injuries have become a growing concern, not just for their immediate effects, but for the long-term damage the brain tsunamis related to concussions can set in motion. Athletes in many sports — skiers, snowboarders, football, soccer and rugby players, as well as equestrians and cyclists — are also vulnerable to these types of head injuries.

It can be difficult to get an accurate picture of the number of concussions sustained while playing sports because concussions are often underdiagnosed. Players may try to minimize or hide their symptoms to keep playing or think their symptoms are unrelated to having sustained a concussion.

The symptoms of a concussion, such as headaches, dizziness, nausea, memory loss or loss of consciousness, rather than the number of diagnosed concussions, may be a better way to predict the long-term cognitive functioning in former athletes, a recent study of retired professional football players found.

Participants’ cognitive functioning was associated with the number of concussion symptoms they recalled having had during their NFL career.

The retired players, who reported experiencing concussion symptoms during their time in the National Football League (NFL), were part of a study led by researchers at Harvard Medical School and McLean Hospital. The NFL players did worse on cognitive tests than a control group of more than 5,000 men who had never played professional football.

The findings, published in Archives of Clinical Neuropsychology, point to the importance of tracking the symptoms of concussion, rather than diagnosed concussions. They also provide supporting evidence that a professional football career can accelerate cognitive decline.

“Former players can be proactive, talk to their providers and educate themselves about symptoms of head injury,” said Ross Zafonte, principal investigator of the Football Players Health Study at Harvard Medical School, in a statement. The findings support efforts to enhance diagnosis and define long-term outcomes of concussion.

More than 350 retired professional football players who were enrolled in the Football Players Health Study participated in the current analysis. The players had been retired from the NFL for an average of 29 years. Their average age was about 54 years old.

On a test of visual memory, the differences in scores between former players with the greatest number of concussion symptoms and those with the fewest symptoms were similar to the differences in scores between a typical 60-year-old and a 35-year-old.

Players participating in the study completed an online test of cognitive functioning, including tests of processing speed, memory and vocabulary. They also answered several questions about demographic information, current health status, when they first started playing football and how long they played professional football. Additionally, they were asked to recall any concussion symptoms they experienced while playing professionally and how many times they were diagnosed with a concussion.

Participants’ cognitive functioning was associated with the number of concussion symptoms they recalled having had during their NFL career. On a test of visual memory, the differences in scores between former players with the greatest number of concussion symptoms and those with the fewest symptoms were similar to the differences in scores seen between a typical 60-year-old and a 35-year-old.

In general, former players fared worse on cognitive tests than the control group. On tests of processing speed, the age-related differences in scores among former players were greater than the differences among those in the control group. Older former players had the lowest scores in these tests.

Poor cognitive functioning was not associated with the number of diagnosed concussions, the number of seasons of play or the age when the retired players first started playing football. Younger retired players may have benefitted more than older players because of increased awareness of and better treatment for head injuries. The researchers did note a lack of information on former players’ cognitive function prior to their injuries limited their findings. “More research is needed that closely matches former players and nonplayers and tracks their cognitive performance across their lifetimes.”