Is exposure to night-time traffic noise a risk factor for purchase of anxiolytic-hypnotic medication? A cohort study.

BACKGROUND Studies suggest that road traffic noise increases risks of sleep disturbances, anxiety and depressive symptoms, but few have focused on psychotropic drug use. We examined whether exposure to night-time road traffic noise in Marseilles (France) is associated with an increased risk of purchasing anxiolytic or hypnotic medications. METHODS Cohort of 190,617 inhabitants of Marseilles (aged 18-64 years) covered by the National Health Insurance Fund. We used the CadnaA noise propagation prediction model to calculate a potential road noise exposure indicator at dwellings for the night-period: Ln. Association between the number of purchases of anxiolytics-hypnotics in 2008-9 and the Ln was analysed with a zero-inflated negative binomial (ZINB) model adjusted for characteristics of individuals (sociodemographic, consultations with general practitioners, presence of chronic psychiatric disorder), prescribers (demographic, specialty, workload) and neighbourhoods (medical density, complaints filed for environmental noise). Analyses were stratified by the deprivation level of the census block of residence to control for the confounding effects of neighbourhood socio-economic status. RESULTS The ZINB model showed a small but significant increase in the risk of purchasing higher numbers of anxiolytics-hypnotics for Ln greater than 55 dB(A) only in the low deprivation stratum. CONCLUSION We found some evidence that potential exposure to night-time road traffic noise might affect individual use of anxiolytics-hypnotics. Further research based on strictly individual approaches is warranted to assess exposure to road traffic noise more precisely and reliably than allowed by noise propagation prediction models.