The risk of concussion and brain damage is now well known in American Football, but what about plain old regular football (or "soccer", as our US readers will call it)?
In a BBC One documentary that aired last night called Dementia, Football and Me, the former Newcastle United striker explored the link between heading a football and the risk of developing dementia.
Match of the Day pundit Shearer is still the Premier League record goalscorer, netting 260 times, with 46 headers among them.
"As someone who played the game for 20 years, and sometimes headed the ball up to 100 times a day in training, I knew that if there was a danger, then I was one of those who could be at risk," Shearer said.
"I went into football knowing that at the end of my career I could probably expect to have some physical issues, which I do - I have dodgy knees, a dodgy back and dodgy ankles.
"But what I never contemplated for a second back then was that there is a chance that heading the ball could affect my brain.
"If that is the case, then people need to be aware of it."
In the doc, which you can watch now on BBC iPlayer, Shearer undergoes testing to see what heading a ball does to his brain.
During the documentary, Professional Footballers' Association chief executive Gordon Taylor admitted that he doesn't know how many of the 50,000 PFA members have dementia.
"Football has a duty to see if there is a causal link, because if there is, and if that could significantly increase the problems in later life, then we need to look at the rules of the game and address it," Taylor said.
There was a strong response to the documentary from viewers:
Shearer surprised some viewers by not calling for a ban of heading in under-11s.
"Our experts think it could be counter productive," he explained later on Twitter.
"Brains at most vulnerable aged 14/15.
"If we ban for under 11's then the first time children head the ball they have no technique at the most vulnerable time. Possibly increasing the risk. I'm saying make educated decisions."
