An epidemiological cohort study of adolescents: Investigating behavioural problems and cognitive functions in relation to traffic noise exposure in Switzerland

Background
Environmental noise is a widespread source of discomfort in everyday life and is an increasing topic of concern for both politicians and the general population. After particulate air pollution, noise exposure is the second highest contributor to the burden of disease of environmental exposures (Hänninen et al., 2014) and the WHO considers children to be at particular risk of the negative consequences of noise (WHO, 2009).
Aim and Objectives
The primary aim of this dissertation is to study how chronic exposure to environmental noise affects adolescent health. The aim was split in four objectives.
1. Analyse the association between transportation noise and adolescent cognitive functions and behaviour problems
2. Describe and quantify the role of transportation noise at home, at school and their relationship
3. Evaluate the role of different noise characteristics in impacting health outcomes
4. Use parameters that modify transportation noise reaching the participants, such as bedroom orientation towards the loudest side of the house, and determine their role in noise exposure.
Methods
All objectives were addressed with two studies that were based on following cohort and methodological approach:
The study cohort consisted of 899 Swiss adolescents aged 10-17 years, from whom data was collected twice with a one-year follow-up through questionnaires and cognitive testing. The study design was cross-sectional and longitudinal; the statistical models were adjusted for relevant confounders and explanatory variables. Outcomes of interest were behaviour problems measured with the strength and difficulties questionnaire (SDQ) and two cognitive functions: memory and concentration. As the only meaningful noise exposure in this particular cohort was road traffic noise (very few participants lived near other sources of transportation noise), this thesis´ focus is road traffic noise exposure as a main exposure. The primary noise metric used throughout the study was the day-evening-night equivalent noise level (Lden). Analyses were conducted for both home and school locations, as well as for combinations of both. Additional analyses were conducted with other noise sources (railway noise, total noise (combination of road, rail and aircraft noise)) and other noise metrics (noise levels at day and night (Lday, Lnight), as well as Number of noise events (Nevt) and the Intermittency Ratio (IR) (Wunderli et al., 2016)). The variable bedroom orientation was used in interaction analyses and sensitivity analyses. Missing data was imputed using the multiple imputation technique (Sterne et al., 2009a).
Results
Both studies show small, but significant associations between environmental noise exposure and both cognitive functions and behavioural outcomes in a Swiss adolescent population.
Behavioural outcomes: In cross-sectional analyses, peer relationship problems were associated with higher levels of road noise at home. Changes in peer relationship problems within a year were not related with higher noise.
Cognitive functions: Worse figural memory was associated with higher noise exposure in cross-sectional analyses, while high road noise exposure at home for a year was associated with a lower concentration constancy. Strikingly, in longitudinal analyses, negative consequences of noise on cognitive functions were mostly observed in adolescents sleeping in bedroom facing towards the loudest street by their house.
Associations were found for road traffic at home, but not at school. Associations were only found for the equivalent sound metrics, not the Nevt and IR.
Discussion and Conclusion
These studies add to the knowledge of road traffic noises association between behaviour and cognition and are the first to show associations for cognition with road traffic noise at home. The fact that a significant association was found between road traffic noise at home with change in concentration constancy within only one year, indicates a potentially strong relationship. This one- year change in adolescents suggests that effects of noise may still happen at the later stages of development. Associations between road noise at school were not found for any outcomes. Following reasons are discussed: (1) due to misclassifications, (2) no relevant road noise reaching the inside of the building or (3) no existing association.