Bob Garfield: And I’m Bob Garfield. This week, a new study concluded that retired NFL players who have suffered from concussions, especially those who lost consciousness, are at higher risk for later-life cognitive decline. That news  strengthens the links between on-field injuries and later neurological problems  -- which has been a courtroom evidentiary hurdle plaguing former players. But beyond the immediate legal liability, the NFL and the rest of the football industry are facing an existential threat as cases of “chronic traumatic encephalopathy” pile up. The NFL claims rule changes and equipment improvements have resulted in a sharp decline in concussions last season but for some players, that’s just not enough. Recently, the league was stunned when star San Francisco 49ers linebacker Chris Borland retired after his rookie season. Borland explains that his own research, not workplace education, that led to his decision.

Chris Borland: I began to look into the research. A high percentage of players suffer from early onset Alzheimer's, or depression. A certain number of brains have been found to have a degenerative neurological disease, and accompanied with the anecdotes of players who'd done things from commit suicide to having memory loss in their 30s, that was enough for me to say thank you, but no thank you.

Bob Garfield: Every restaurant in the world, somewhere around the restrooms has posters that say, "employees must wash their hands." Now they kind of blend into the background, but they're there. And I wonder if even in the background, players were kept aware of chronic brain encephalopathy, with all of the really horrifying symptoms that you've described.

Chris Borland: Yeah, there's a poster up in the locker room about tackling technique and avoiding injury, but I think players are sometimes willfully ignorant. "Yeah, I understand there's something going on, but I'm focused on this week." If we can do a better job of informing young guys, I mean even before high school, that's huge, because once you're a successful high school player what's to stop you from going to college, if you're successful in college, of course you'll want to play in the NFL. I even found myself thinking this past year, you know I'm probably OK, I probably could play a second year. And then I'm sure I'd have that conversation in year two, and then if all of a sudden if I'm fortunate enough to stay healthy, it's year six, and maybe it's too late for me to avoid some things down the road.

Bob Garfield: Tell me about denialism. You know in the way climate change denial has become a kind of fixture of conservative politics, is there a constituency for head injury denialism?

Chris Borland: Yeah I think there is. There's a small separation between correlation and causation, and if you focus on that sliver of a gap between the two, yes, technically no one can prove that yet, but I think it's counter-productive to just deny that something's going on.

Bob Garfield: For many decades, before there was actual biological linkage between smoking and cancer, there was an endless amount of epidemiological evidence connecting the two. And yet, the tobacco industry referred to a controversy surrounding tobacco- there was no controversy. And of course eventually science caught up to the epidemiology, what about at the NFL? Is there anybody claiming even at the league and the TV networks, that this is a controversial subject?

Chris Borland: Well I think a lot of people have made the analogy to Big Tobacco, but Big Football and proponents of football say that there's measures you can take to decrease the risks. And there are, but you know, they also made filtered cigarettes so, I don't know how much you can change football and keep it football, but individuals need to be informed and do what's right for them. I don't think you can look from the top down and expect drastic changes.

Bob Garfield: If you have sons, you gonna let them play football, ever?

Chris Borland: I think I'd be more apt, I think, to let my son play if he weren't that talented. But the concern for me is getting into something where you have a great experience in high school, then colleges come calling, and they're going to pay your tuition, and then imagine you have a great experience in college. It'd be really tough for anyone to say hey, son, stop playing. And then the same is true of the next level.

Bob Garfield: And the hits add up. [Chris Borland: Yeah.] And up, and up and up.

Chris Borland: Yeah, the violence is captivating, I understand that as much as anyone, but perhaps it goes too far.

Bob Garfield: Well Chris, all the best to you and thank you very much for being with us.

Chris Borland: Thank you Bob, I appreciate you having me.