Yes, it was from the harsh blows to his head that he had when he was fighting. If it is affecting NFL Football players the blows to their heads, why not for the great boxer Muhammad Ali who was boxing and took many punches to his head and had fallen many times.
Muhammad Ali was a professional athlete and as such, he trained hard and vigorously. He was in excellent condition and should not have been a candidate for dementia. That's why I believe his boxing career was to blame. A person's body is not meant to withstand that kind of abuse. Even though he was strong and in good shape, I believe his many fights took their toll on him.
Yes, I think it is believable that Muhammad Ali's dementia was caused by his boxing career. Repeated blows to the head had to have had an impact on his health, and it is not surprising that he developed a brain disorder. While it is difficult to say whether boxing was the only cause, it definitely seems to have played a role.
He was diagnosed with Parkinson's, not dementia if you think that was caused by his boxing your going to be wrong again. If your going to throw out things like this, do your research first. He was or never seemed punchy,but he sure does all the symptoms of Parkinson's, as do Michel J Fox, who never boxed.