In the gospel reading from last Tuesday, Jesus heals a man who was apparently unable to walk for many years (John 5:1-3,5-16). Afterward, Christ warns him:
|‘Now you are well again, be sure not to sin any more, or something worse may happen to you.’|
I'd read in some commentary someplace (can't remember by whom) that sin and sickness were commonly associated in ancient times. But it would not be a very Christian attitude to allude irrational superstition to the Son of God. There is, in fact, a lot of empirical evidence for the association.
I can think of a few sins that involve behavior that risks one's health. Violence has its own risks, and a violent life, and certainly when unwarranted (not in war or law enforcement), carries unwarranted extra risks. Substance abuse? Sexual promiscuity certainly comes to mind, too. It is now considered conventional medical wisdom (for example) that there is a strong correlation between promiscuity with multiple partners and STD contraction. If environmentalists can cite violations against the ecosystem, why can't we cite destructive human behavior, too? It doesn't even take being a Catholic to understand that. Perhaps all you need are facts.