Serum cotinine levels and diabetes mellitus in never smokers

The aim of the current study is to examine the association of environmental tobacco smoke (ETS) exposure evident by serum cotinine level, and diabetes mellitus in never smokers. Previous studies suggest that active tobacco cigarette smoking is associated with diabetes mellitus risk. However it is not clear if the low-level "background" ETS exposure is associated with diabetes among never smokers.

We present evidence from five independent replications based on the US nationally representative National Health and Nutrition Examination Surveys (NHANES) conducted 2003-12. Our exposure of interest is ETS exposure among never smokers, measured by serum cotinine levels (ng/mL), and our main outcome is diabetes mellitus assessed via self-reported physician-diagnosis, current use of insulin and/or oral hypoglycemic medications, plasma fasting glucose levels ≥126mg/dL or glycohemoglobin levels ≥6.5%. The conceptual model encompassed age, sex, ethnic self-identification, education, poverty-income ratio, alcohol drinking, total cholesterol and body mass index.

In never smokers, higher serum cotinine levels were positively associated with diabetes mellitus (the meta-analytic summary estimate is 1.2, 95% CI=1.1, 1.2). This association was not evident among never smokers with cotinine levels below 3ng/mL.

These replications help sustain evidence of ETS-diabetes mellitus association, which might be explained by shared psychosocial characteristics. Prospective studies with appropriate biomarkers are needed to further investigate this association.