Indoor and outdoor road traffic noise and incident diabetes mellitus: Results from a longitudinal German cohort study

Abstract

Background: Road traffic noise affects a large number of people in urbanized areas. Recent epidemiological evidence indicates that environmental noise exposure may not only be associated with cardiovascular but also with cardio-metabolic outcomes. This prospective cohort study investigated the effect of outdoor and indoor residential road traffic noise on incident type 2 diabetes mellitus (T2DM). Methods: We used data from 3,396 participants of age 45-75 years of the Heinz Nixdorf Recall study being non-diabetic at baseline (2000-2003). T2DM was defined via blood glucose level, incident intake of an anti-diabetic drug during follow-up or self-reported physician diagnosis at follow-up examination (2005-2008). Weighted 24-h (Lden) and night-time (Lnight) mean road traffic noise was assessed according to the European Union directive 2002/49/EC. Road traffic noise exposure indoors was modeled taking into account the participants' room orientation, ventilation behavior and window insulation (n = 2,697). We applied Poisson regression analyses to estimate relative risks (RRs) of incident T2DM, adjusting for demographic characteristics, lifestyle factors, and air pollution exposure (NO2 or PM2.5). Results: A 10-dB(A) increase in outdoor road traffic noise (Lden) was associated with an RR of 1.09 (95% confidence interval, 0.96-1.24) for T2DM in the fully adjusted model. Models including PM2.5 or NO2 yielded RRs of 1.09 (0.96-1.24) and 1.11 (0.97-1.27), respectively. In analyses with road traffic noise (Lden) exposure indoors, we observed similar RRs with smaller confidence intervals (1.11 [1.01-1.21]). Conclusions: Our analyses suggest that long-term exposure to indoor and outdoor road traffic noise may increase the risk of developing T2DM, independent of air pollution exposure.