How dangerous is professional football to the long term health of its players? Apparently, it is the opposite of dangerous:

That [study], conducted by the National Institute for Occupational Safety and Health (and then peer-reviewed), compared mortality among retired football players and nonathletes matched for age and race and found that the ex-athletes were dying about half as often as one might expect. In other words, the health risks associated with playing football were being more than outweighed by the benefits of being a pro athlete—excellent training and nutrition, a good salary, top-quality medical care, and so on.