Objective

Only a few prospective studies have examined the relationship between the frequency of cigarette smoking and the incidence of diabetes mellitus. The purpose of this study was to determine whether greater frequency of cigarette smoking accelerated the development of diabetes
mellitus, and whether quitting reversed the effect.

Methods Data were collected in the Cancer Prevention Study I, a prospective cohort study conducted from 1959 through 1972 by the American Cancer Society where volunteers recruited more than one million acquaintances in 25 US states. From these over one million original participants, 275 190 men and 434 637 women aged L30 years were selected for the primary analysis using predetermined criteria.

Results As smoking increased, the rate of diabetes increased for both men and women. Among those who smoked L2 packs per day at baseline, men had a 4596 higher diabetes rate than men who had never smoked; the comparable increase for women was 74%. Quitting smoking reduced the rate of diabetes to that of non-smokers after 5 years in women and after 10 years in men.

Conclusions A dose-response relationship seems likely between smoking and incidence of diabetes. Smokers who quit may derive substantial benefit from doing so. Confirmation of these observations is needed through additional epidemiological and biological research.

Q1 : What type of study design is described in the abstract?

Q2 : How did the authors define primary exposure? Be specific.

Q3 : Was the relative risk higher in men or women?

Q4 : Which Bradford-Hill criterion of causality was cited in the abstract?

Q5 : Provide 1 limitation of the selected study design