If you don't eliminate the bias caused by smoking, it will artificially inflate the risk of dying among the lean and underestimate the risk of dying in the overweight,

The effect of cigarettes on the risk of disease is so powerful and it's so difficult to control for factors like the intensity and duration of smoking that the only way to eliminate the bias is to look at people who have never smoked,

Active cigarette smoking is established by us -- and, really, almost everyone -- as being the single largest risk factor for hardening of the arteries.

Smoking appears to confer a modest elevation in breast cancer risk, ... Certainly this relationship is not as strong as the relationship between smoking and lung cancer or smoking and heart disease, but breast cancer may be another disease to add to the long list of diseases associated with smoking.

There was no significant difference in risk between men who quit smoking and those who continued to smoke.

The evidence is now compelling and irrefutable,