this is a bit of a dumb comment I think; it's a bit like saying you've known people who've headed a soccer ball repeatedly every weekend for years, so you find

this is a bit of a dumb comment I think; it's a bit like saying you've known people who've headed a soccer ball repeatedly every weekend for years, so you find it hard to believe that heading a cement block could be harmful. It's a different chemical, with different effects. The best way to determine those effects is through properly controlled trials.