Former National Football League players are more likely to suffer from brain damage and lose memory and attention abilities than non-athletes, according to a new study.

Previous research on football players and war veterans has shown a significant association between concussions and brain damage. However researchers in the present study found that a few players who had suffered from many head blows didn't have any mental disorders after retirement.

The study involved 34 former football players. Researchers assessed mental abilities of these players and compared them to men who didn't play the sport.

In the study group, 20 players had no symptoms of a mental illness. One of them was Daryl Johnston who suffered numerous blows to the head, HealthDay reported.

Eight participants were reported to suffer from depression, eight were diagnosed with mild cognitive impairments, four with cognitive deficits and two with dementia.

The study found that players who were cognitively impaired performed poorly in tests of naming, word finding and visual or verbal memory.

"The damage can occur from head injuries because the brain is shaken or twisted, and that stretches the white matter," one of the study authors, Dr. John Hart Jr., medical science director of the Center for BrainHealth at the University of Texas at Dallas, told HealthDay.

Brain scans of 26 former NFL players along with 26 other study participants were also conducted. Researchers found that former NFL players had more damage to the white matter in the brain compared to other participants. Hart explained that white matter connects the gray areas of the brain. Brain scans showed that there was a difference in blood flow in certain areas of the brain. For example, an area associated with word-finding had an increase in blood flow, while an area associated with verbal memory had decreased blood flow.

"Cognitive deficits and depression appear to be more common in aging former NFL players compared with healthy controls. These deficits are correlated with white matter abnormalities and changes in regional cerebral blood flow," study authors concluded.

In an interview given published in JAMA, Hart said that nowadays, the guidelines for football players are designed in way that removes the potential damage from head injuries.

The study is published in the journal JAMA Neurology.