Analysis of the effect of tobacco upon human longevity after age 30 using a random sample of 6813 men (grouped as nonusers of tobacco moderate smokers and heavy smokers) showed a significant impairment of survivorship among smokers with the impairment increasing as frequency of smoking increased. Beyond age 70 however differences in the mortality rates of the 3 groups practically disappeared possibly because of the immunity developed by resistent specimens against the harmful effects of tobacco.
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Raymond Pearl (1938) studied this question.