There are conflicting and limited data on associations between smoke cessation and risk of coronary heart disease (CHD) and chronic respiratory illnesses. There are consistent results of a decreasing risk for CHD with increasing duration of smoking cessation. However, the duration of cessation of smoking needed for ex-smokers to have a comparable CHD risk to never smokers varied widely from 1 year to more than 15 years. This requires better and larger designed studies and more accurate exposure measures of tobacco smoking. There is consistency that quitting smoking can decrease the risk of CHD to be similar to that of never-smokers. For the association between smoking cessation and respiratory illnesses there is consensus that the damage can be irreversible especially to the airway lining and structure. Forced expiratory volume seems to improve after cessation as shown by several studies of COPD diagnoses participants. However, the pathological damage to the structure of airways as a result of smoking can improve with longer cessation periods, but may become permanent and never returns to normal according to several studies. Cumulative tobacco smoke exposure in relation to respiratory illnesses seems to be more important than current smoking status. There is no doubt that smoking cessation will positively impact the health of smokers who quit and the earlier the quitting the lesser the long-term damage. More studies on mechanisms and accurate dose-response associations between quitting and coronary and respiratory diseases are still needed.
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