Recent research is starting to show athletes don't have to sustain a concussion to suffer brain injuries, mild repeated bumps to the head even from heading can cause injury over time.
As a brain injury researcher myself I don't think we should wait for the research to complete to take action because research is never complete and many athletes will already have sustained injuries.
Some soccer football programs are going so far as to ban heading:
As an alternative to an outright heading ban is to practice heading with a lighter rubber ball to develop technique, strengthen neck muscles, and reduce the total number of heading impacts. This is especially important for younger players who's brains are still developing. With light rubber ball practice the players will have the strength and control to use correct form possibly reducing the risk of injury when they are older and in games and do head the ball.
[Possible heading practice ball: http://www.amazon.com/Spalding-High-Bounce-Ball-Pack-4/dp/B001R58J1Y/ref=pd_sim_t_5?ie=UTF8&refRID=1GQWVBTMATB132WB4QXE]