Cancer aside! The heart disease risk for a light smoker (1-4 per day) is 3-times that of a non-smoker.

Cancer follows a risk curve that is a bit more like a linear dose-response. For instance, for those smoking >20 cigarettes per day, the risk of dying from lung cancer is >23 times higher, whereas those who smoke 1 to 4 cigarette per day have a 3-fold higher risk than nonsmokers.