Big hits may be par for the course in football, but the impact some players sustain from head injuries may follow them for years to come, new study finds.

A published Thursday in the Archives of Clinical Neuropsychology has found that NFL players who experienced concussion symptoms during their years on field showed reduced cognitive function long after retiring.

"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," said study senior author Laura Germine, director of the Laboratory for Brain and Cognitive Health Technology at McLean Hospital and associate professor of psychiatry at Harvard Medical School, in a . "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."

Researchers assessed more than 350 former NFL players who were studied for an average of 29 years following their retirement from professional football, examining their cognitive functions such as episodic memory, sustained attention, processing speed and vocabulary.

To find out which players had experienced concussion symptoms while playing, the researchers asked them if they had experienced symptoms such as headaches, nausea, dizziness, memory problems, or visual problems.

Players were also asked to think back on their careers and report if they had ever lost consciousness while playing, and if they were diagnosed with a concussion by a medical professional at any point.

The results of these assessments showed that players who said they had experienced concussion symptoms during their career demonstrated worsened cognitive function overall.

To put these results in perspective, when looking at visual memory scores between former players with the highest versus the lowest reported concussion symptoms, they found their difference in cognitive function was comparable to that of a typical 35 year old and 60 year old.

"Former players can support their cognitive health as they age by taking proactive steps and continuing to consult with their providers and educate themselves on symptoms of head injury,鈥 said Ross Zafonte, principal investigator of Harvard University's Football Players Health Study, of which this new study is a part of, in a press release.

Neither the number of diagnosed concessions nor the length of a player's football career appeared to impact the results.

To understand how playing football contributes to the decline in cognitive function later in life, researchers conducted a follow-up analysis that compared the former NFL players to more than 5,000 males from the general population who were not football players.

This comparison concluded that the NFL players' cognitive function generally worsened to a higher degree as they aged, more than the non-players.

A previous published in 2010 reported on the prevalence of concussions in the sport, finding that there are approximately 140 concussions reported each NFL season, plus it鈥檚 estimated that one player suffers a concussion every five games.

鈥淔or researchers and providers, these findings support efforts to develop ways to enhance diagnosis and define long-term sequalae of concussion,鈥 said Zafonte.