My dad smoked 4 packs of cigarettes a day to the day he died. The doctor told me he could not believe how clear his lungs were as much as he smoked. Some people just have natural tolerances for certain things.
Take a look at Keith Richards for example....
Can you believe this guy is already 63... amazing! He doesn't look a day over 35 if you ask me. Who Knew that heavy doses of smack, booze and cigarettes would act as health elixirs for this lucky guy.