Secondhand smoke, obesity, and risk of type II diabetes among California teachers

To examine if secondhand smoke (SHS) is associated with elevated risk of type II diabetes among California teachers. We also aim to determine if overall and central obesity are mediators or effect modifiers of this association.

Using data from the California Teachers Study, conducted in 1995-2013 in California public schools, we obtained information on SHS exposure among 39,887 lifetime nonsmokers. The association between SHS and incident diabetes after 17 years of follow-up was assessed using Cox regression models. The mediation and modification effects of BMI and waist circumference on this association were tested.

At baseline, 70.2% of the nonsmokers reported exposure to SHS. Higher intensity, duration, and intensity-years of exposure to SHS were associated with higher multivariate adjusted risk of incident diabetes in a dose-response manner (hazard ratio = 1.28; 95% confidence interval, 1.11-1.48 for highest quartile vs. lowest quartile of exposure; P = .001 for trend). Participant's waist circumference (measured 2 years after baseline) could explain greater than 50% of the association between SHS and diabetes.

SHS exposure is associated with increased risk of type II diabetes among nonsmokers of California teachers with obesity being a potentially important mediator but not an effect modifier for this association.