Bjerregaard BK, Raaschou-Nielsen O, Sorensen M, Frederiksen K, Tjonneland A, Rohrmann S, Linseisen J, Bergman MM, Boeing H, Sieri S, Palli D, Tumino R, Sacerdote C, Bueno-De-Mesquita HB, Buchner FL, Gram IT, Braaten T, Lund E, Hallmans G, Agren A, Riboli E. The effect of occasional smoking on smoking-related cancers: in the European Prospective Investigation into Cancer and Nutrition (EPIC). Cancer Causes Control. 2006; 17(10):1305-1309.
OBJECTIVE: Most studies on tobacco smoking have focused on daily-smokers. Occasional smokers, who have never smoked daily, have often been included in the reference group of never-smokers. We have investigated the association between occasional smoking and cancer of the bladder, kidney, pancreas, upper aero-digestive tract and lung.
METHODS: The study population consisted of 158,488 persons, who provided information on occasional smoking, within the European Prospective Investigation into Cancer and Nutrition (EPIC), 780 of whom developed a smoking-related cancer. We used Cox proportional hazard model, stratified by gender and country to estimate incidence rate ratios (IRR) for smoking-related cancers.
RESULTS: The results suggest that occasional smokers have a higher risk of bladder cancer (IRR: 1.92, 95% confidence interval (CI) 0.93-3.98) and of the major smoking-related cancers combined (IRR: 1.24, 95% CI 0.80-1.94) than true never-smokers. Including occasional smokers in the reference group resulted in a lower risk estimate for former and current smokers.
CONCLUSIONS: Occasional smoking should be discouraged