Do we need more evidence on the harm done by smoking? Smoking is a major contributor to common diseases such as heart attack, stroke, peripheral vascular disease, and chronic obstructive pulmonary disease. In addition, most lung cancers are caused by smoking and it is also a risk factor for cancers of the breast and bowel. The blogger who wrote last year that smoking bans were illiberal and “justified by bullshit science”1 will have gained little informed support. Smoking costs life and limb; smokers are even prematurely wrinkly.2

The linked study by Parsons and colleagues (doi: 10.1136/bmj.b5569) adds more to the evidence. The meta-analysis of the effect of continued smoking after a diagnosis of mostly early stage lung cancer shows that continued smoking substantially increases the risk of death, and that a large proportion of the increased risk is the result of cancer progression rather than cardiorespiratory disease. The estimated effects are large, with five year survival in “quitters” in the order of 60-70% compared with about …