I'm wondering what effect of smoking can be prevented?

Why do you ask?: You've being played for a sucker if you think that any medication, exercise, supplement or healthy habit might undo the damage you've done to your lungs smoking. The lost elasticity will never return. The cancer risk will reverse only in part and after a few decades following cessation. Tobacco companies have sometimes claimed various vitamins / foods are protective. It's all lies. Please stop.