Association between passive and active smoking and incident type 2 diabetes in women

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.Smoking is one of the leading causes of avoidable death globally (1). The disease burden attributable to smoking already is enormous, with ~6 million premature deaths worldwide each year, and is projected to grow substantially across the century without an end to the pandemic (1). Diabetes also is a global health priority. The International Diabetes Federation has predicted that the number of individuals with diabetes will increase from 240 million in 2007 to 380 million in 2025 (2).Accumulating evidence has identified a positive association between active smoking and risk of type 2 diabetes (3), whereas few studies had information on passive smoking. Data from the Third National Health and Nutrition Examination Survey 1988–1991 suggest that ~90% of nonsmokers have detectable levels of serum cotinine, a sensitive marker for tobacco exposure (4). Therefore, previous studies linking active smoking with diabetes risk might have underestimated the magnitude of the true association because individuals exposed to passive smoke would be in the reference group. The few studies that simultaneously examined the relative associations of passive and active smoking on diabetes risk (5,6) were limited by relatively short follow-up periods, limited information on potential confounders, and lack of information on smoking quantity or change in smoking behavior over time. Therefore, we prospectively investigated the association between passive and active smoking and the risk of incident type 2 diabetes over 24 years of follow-up among 100,526 women from the Nurses’ Health Study (NHS).