It is suggested both duration (years of cigarette use) and intensity (cigarettes per day) determine the negative health effects of smoking.43
The 2014 report of the US Surgeon General concluded that “reducing the number of cigarettes smoked per day is much less effective than quitting entirely for avoiding the risks of premature death from all smoking-related causes of death.”64
Use of electronic cigarettes by cigarette smokers to cut down on the number of cigarettes smoked per day is likely to have much smaller beneficial effects on overall survival compared with quitting smoking completely.43
This situation is particularly likely to exist for cardiovascular disease. Light smoking, even 1 to 4 cigarettes per day, is associated with markedly elevated risk of cardiovascular disease.65 In addition, e-cigarettes deliver loads of fine particles similar to those of conventional cigarettes. Above certain intensity, the specific levels of exposure may not cause significant differences in risk for cancer. Doll and Peto66 found a dose-response relationship between duration of smoking and number of cigarettes smoked per day and risk of lung cancer, with models suggesting the impact of duration to be greater than that of intensity. Using participants from the Cancer Prevention Study II, Flanders et al67 found a greater increase in lung cancer mortality with a greater duration of cigarette smoking compared with a greater intensity of smoking. Overall, this data suggests that lung cancer mortality increases more with additional years of smoking than additional cigarettes per day. Thus, if dual use of e-cigarettes and cigarettes results in reductions in the number of cigarettes per day for current smokers, any reduction malignancy risk will be less than proportional to the reduction in cigarette consumption because of the (likely larger) importance of duration of smoking.43
“Even though e-cigarettes are known to be much less harmful for health than tobacco smoking products, nobody knows what their long-term health and addiction consequences might be.”
– Roswell Park Cancer Institute, Buffalo, New York
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