PHILADELPHIA (CBS) - Coinciding with the start of the NFL season, a new study sheds some light on how dangerous the sport can be for the men who play it for a living.

A report in the Journal Neurology examined over 3,400 retired players who played five or more seasons in the league, and the study finds these athletes are four times more likely than other men their age to die of Alzheimer’s disease or ALS.

In addition, NFL players are more likely to have a problem called Chronic Traumatic Encephalopathy (CTE) which is a buildup of protein seen in autopsied brains of former athletes who played in contact sports.

The report also found that those who played in “high speed positions” like running back and wide receiver also had an even greater problem. The study also raises concerns for people who have younger children who are athletes who may be in sports where head trauma is part of the picture.