Objective: Accumulating evidence has identified a positive association between active smoking and the risk of diabetes, but previous studies had limited information on passive smoking or changes in smoking behaviors over time. This analysis examined the association between exposure to passive smoke, active smoking, and the risk of incident type 2 diabetes among women.
Research design and methods: This is a prospective cohort study of 100,526 women in the Nurses' Health Study who did not have prevalent diabetes in 1982, with follow-up for diabetes for 24 years.
Results: We identified 5,392 incident cases of type 2 diabetes during 24 years of follow-up. Compared with nonsmokers with no exposure to passive smoke, there was an increased risk of diabetes among nonsmokers who were occasionally (relative risk [RR] 1.10 [95% CI 0.94-1.23]) or regularly (1.16 [1.00-1.35]) exposed to passive smoke. The risk of incident type 2 diabetes was increased by 28% (12-50) among all past smokers. The risk diminished as time since quitting increased but still was elevated even 20-29 years later (1.15 [1.00-1.32]). Current smokers had the highest risk of incident type 2 diabetes in a dose-dependent manner. Adjusted RRs increased from 1.39 (1.17-1.64) for 1-14 cigarettes per day to 1.98 (1.57-2.36) for ≥25 cigarettes per day compared with nonsmokers with no exposure to passive smoke.
Conclusions: Our study suggests that exposure to passive smoke and active smoking are positively and independently associated with the risk of type 2 diabetes.