WHICH FEATURES OF SMOKING DETERMINE MORTALITY RISK IN FORMER CIGARETTE SMOKERS WITH DIABETES

OBJECTIVE - The effects of quitting smoking on mortality risk in indiv iduals with diabetes is unknown and may differ from the benefits obser ved in the general population. We therefore determined the mortality r isks in ex-smokers with diabetes, compared with subjects who have neve r smoked, by the number of years since quitting, the number of cigaret tes smoked, and the number of years of smoking. RESEARCH DESIGN AND ME THODS - An international cohort study of 4,427 individuals with diabet es was studied. Baseline examinations were performed in 1975-1977 when smoking habits were determined by questionnaire. Mortality follow-up continued until 1988. RESULTS - All-cause mortality risks were higher for recent quitters (1-9 years; relative risk [RR], 1.53 [95% CI 1.19- 1.97]; P = 0.001) than for those who quit earlier (greater than or equ al to 10 years; RR, 1.25 [95% CI 1.03-1.52]; P = 0.02), compared with subjects who have never smoked. These risks were highest in those who had smoked the longest (greater than or equal to 30 years: RR, 1.66 [9 5% CI 1.22-2.26]; P = 0.001; vs. 1-9 years: RR, 1.17 [95% CI 0.85-1.60 ]; P = 0.3). Risks were also highest in those who had smoked the most and least number of cigarettes. Adjustment for key confounders, which included a previous history of heart disease, proteinuria, and blood p ressure, did not materially affect these relationships. CONCLUSIONS - Quitting smoking does reduce mortality risk in ex-smokers with diabete s, but risks remain high several years after quitting and are highly d ependent on thr duration of smoking. Thus, individuals with diabetes w ho smoke should be encouraged to quit as soon as possible in the cours e of disease.