Long-Term Exposure to Traffic Related Noise and Incidence of Diabetes: A Danish Nurse Cohort Study

Abstract

Background/Aim: Well-established risk factors for diabetes include diet, body mass index and physical activity, all of which are individually modifiable factors. However, recent evidence suggests that environmental factors including road traffic noise and air pollution may affect the risk of developing diabetes. Here we examine whether road traffic noise is associated with diabetes incidence, when accounting for air pollution exposure. Methods: 28,731 female nurses from the Danish Nurse cohort (>44 years old at recruitment in 1993 or 1999) were linked to the Danish Diabetes Register with information on incidence of diabetes from 1995 until 2013. The annual mean weighted levels of 24-hour average road traffic noise (Lden) were modeled with Nord2000. Annual mean concentrations of PM2.5 at residence were modeled with Danish AirGIS system. Cox proportional hazards regression models with age as underlying time was used to examine the association between annual mean Lden at the study baseline (1995 or 1999) and the incidence of diabetes in a model adjusted for lifestyle factors and additionally, for annual mean PM2.5 concentration at the study baseline (1995 or 1999). Results: Of 23,169 nurses free of diabetes at the cohort enrolment, 1,099 developed diabetes during a mean follow-up of 15.2 years. The diabetes risk was increased among those exposed to high (>57 dB) when compared to low (≤ 47 dB) Lden in crude model (hazard ratio (HR); 1.25 (95% confidence interval (CI): 1.06-1.47), and adjusted for diabetes risk factors (1.18; 1.00-1.39). However, the effect of Lden diminished (HR 1.03; 0.86-1.24) when adjusting for PM2.5. In the fully adjusted model, an interquartile range (3.89 µg/m3) increase in PM2.5 was associated with 18% (HR: 1.18, 95% CI: 1.09-1.29) increase in diabetes risk. Conclusions: We detected association between road traffic noise and diabetes risk, but which disappeared after adjustment for PM2.5.