How does smoking shorten your life?

For smoking, it would be unwise to say that it "shortens" one's life. Although studies give the answer that a cigarette takes 11 minutes off of your life, this is not necessarily correct. It was obtained through math, paying no attention to how the body functions. If you were to smoke on a regular basis for the rest of your life, yes, each one would take about 11 minutes off, but if you quit before any permanent damage was done and you have enough time left in you to keep on living, then your lungs will heal themselves right as rain (given proper time that is).