That depends on the way it is linked. If it's linked causally in the opposite direction, your advice is quite dangerous. Meaning that if higher per capita head injuries are causing more helmet wearing in sub populations (maybe because they see more news about deadly injuries), than your advice is for people in those sub populations to not wear their helmets.

So it's relevant information, but the direct effect of "wearing a helmet cuts the risk of serious head injury by 60% and a deadly brain injury by 71%" is more important information.