how can steroids shorten life spans?

Answer 1

Anything that speeds up your bodies heart rate or alters the bodies natural growth can shorten the life span.

Answer 2

I assume you mean prescribed steroids at therapeutic levels....steroids are immunosuppressive drugs. They lower your immunity and can allow opportunistic infections to become deadly. This risk is outweighed by the fact that they also suppress the effects of whichever condition they are being prescribed to treat. As for illegal steroids to boost muscle mass--I cannot answer. I have never had reason to study that.