A preliminary study by Boston University researchers shows a link between the number of hits a player takes in youth, high school and college football and the development of cognitive difficulties as an adult.

The authors warn that more research is needed before parents or policy-makers draw conclusions about the safety of amateur football.

The study was published Thursday in the Journal of Neurotrauma.

Dr. Robert Stern of the BU School of Medicine says the study is the first of its kind to look at the connection between the total number of head impacts an athlete sustained and later-in-life difficulties such as depression, apathy and behavioral dysfunction.

But he stressed it is meant to spur further research and not guide individuals when deciding whether football is safe for them.

Journal information: Journal of Neurotrauma