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Introduction
Over the past decade, there has been increasing evidence that transportation noise exposure, such as road traffic noise, leads to poorer cardiovascular health. A recent review suggested that risk for adverse cardiovascular health outcomes, such as heart attacks and stroke, increased by 7–17% for a 10-dB increase in road traffic noise exposure (Basner et al. 2014). This increase is biologically plausible (Babisch 2014; Recio et al. 2016): Noise exposure is hypothesized to cause physiological stress reactions in individuals (Recio et al. 2016), which in turn lead to increases in cardiovascular disease risk factors such as blood pressure, blood fats, and blood glucose concentrations. These risk factors lead to increased risk of high blood pressure and arteriosclerosis (e.g., narrowing of arteries because of fat deposits) and are related to serious events such as heart attacks and strokes (Babisch 2014; Basner et al. 2014). Noise exposure at night may also interfere with sleep, which may also affect diabetes via effects on glucose regulation, appetite, and energy expenditure (Eriksson et al. 2014).
Given the widely accepted causal pathways for noise and cardiovascular health (Babisch 2014; Recio et al. 2016), we would expect to observe associations between noise exposure and metabolic risk factors. To date, relatively few studies have examined the influence of transportation noise exposure on metabolic risk factors for cardiovascular health such as body mass index (BMI), waist circumference, central obesity (Oftedal et al. 2015; Pyko et al. 2015), and blood fats (Sørensen et al. 2015), with studies suggesting small effects on these outcomes. Diabetes is another metabolic risk factor that places an enormous burden on the Canadian population (PHAC 2011) but has received only limited study. A cohort study of 57,053 Danish adults, 50–64 y old, who were exposed to annual average road traffic noise ranging from 48–70 dB found that a 10-dB higher level of road traffic noise during the 5 y preceding diagnosis was associated with an increased risk of incident diabetes identified from registry data {incidence rate ratio of 1.11 [95% confidence interval (CI) 1.05, 1.18]} after adjusting for age, sex, body mass index, waist circumference, education, air pollution (nitrogen oxides), and lifestyle characteristics (Sørensen et al. 2013).
One potential confounding factor in studies examining associations of environmental noise on diabetes is...