The two most notable ailments that have been linked with smoking are lung cancer and heart disease. Statistically, smokers are at increased risk for both of these, though not as much so as some of the propaganda out there would suggest. Certain types of cancer or heart disease are statistically more common in smokers or tend to appear at earlier ages, but again, not as much as some Antismoking propaganda would suggest. The disease is relatively unknown, even among heavier smokers, until later in life. However, at least some of these deaths are due not to smoking itself, but to the lifestyle choices that smokers make.
Smokers tend to eat fattier foods, drink more alcohol, use more illegal drugs , and exercise less.
When such factors are taken into account the difference in life expectancy between a smoker and a nonsmoker decreases significantly. Genetics, diet, and socio-economic status all can surpass moderate smoking in their effects on our longevity. Not so much as they are generally over-emphasized elsewhere. Recent studies indicate that most people vastly overestimate the health risks of smoking. If one derives enough enjoyment from smoking it is not at all irrational to balance that enjoyment against the risks and continue smoking.