Road traffic noise is a prevalent and known health hazard. However, little is known yet about its effect on children’s cognition. We aimed to study the association between exposure to road traffic noise and the development of working memory and attention in primary school children, considering school-outdoor and school-indoor annual average noise levels and noise fluctuation characteristics, as well as home-outdoor noise exposure.
We followed up a population-based sample of 2,680 children aged 7 to 10 years from 38 schools in Barcelona (Catalonia, Spain) between January 2012 to March 2013. Children underwent computerised cognitive tests 4 times (n = 10,112), for working memory (2-back task, detectability), complex working memory (3-back task, detectability), and inattentiveness (Attention Network Task, hit reaction time standard error, in milliseconds). Road traffic noise was measured indoors and outdoors at schools, at the start of the school year, using standard protocols to obtain A-weighted equivalent sound pressure levels, i.e., annual average levels scaled to human hearing, for the daytime (daytime LAeq, in dB). We also derived fluctuation indicators out of the measurements (noise intermittency ratio, %; and number of noise events) and obtained individual estimated indoor noise levels (LAeq) correcting for classroom orientation and classroom change between years. Home-outdoor noise exposure at home (Lden, i.e., EU indicator for the 24-hour annual average levels) was estimated using Barcelona’s noise map for year 2012, according to the European Noise Directive (2002). We used linear mixed models to evaluate the association between exposure to noise and cognitive development adjusting for age, sex, maternal education, socioeconomical vulnerability index at home, indoor or outdoor traffic-related air pollution (TRAP) for corresponding school models or outdoor nitrogen dioxide (NO2) for home models. Child and school were included as nested random effects.
The median age (percentile 25, percentile 75) of children in visit 1 was 8.5 (7.8; 9.3) years, 49.9% were girls, and 50% of the schools were public. School-outdoor exposure to road traffic noise was associated with a slower development in working memory (2-back and 3-back) and greater inattentiveness over 1 year in children, both for the average noise level (e.g., ‒4.83 points [95% CI: ‒7.21, ‒2.45], p-value < 0.001, in 2-back detectability per 5 dB in street levels) and noise fluctuation (e.g., ‒4.38 [‒7.08, ‒1.67], p-value = 0.002, per 50 noise events at street level). Individual exposure to the road traffic average noise level in classrooms was only associated with inattentiveness (2.49 ms [0, 4.81], p-value = 0.050, per 5 dB), whereas indoor noise fluctuation was consistently associated with all outcomes. Home-outdoor noise exposure was not associated with the outcomes. Study limitations include a potential lack of generalizability (58% of mothers with university degree in our study versus 50% in the region) and the lack of past noise exposure assessment.
We observed that exposure to road traffic noise at school, but not at home, was associated with slower development of working memory, complex working memory, and attention in schoolchildren over 1 year. Associations with noise fluctuation indicators were more evident than with average noise levels in classrooms.
Why was this study done?
* Exposure to aircraft noise has been associated with impaired cognitive development in schoolchildren, and experiments have also observed that animals exposed to moderate or high noise levels for 4 to 30 days suffer changes in the brain.
* Road traffic noise is the most common noise source and many children are exposed to it at school; however, it is still unclear whether it affects children’s cognitive development, including important aspects such as working memory or attention.
* Moreover, while previous studies have assessed exposure to the average noise level outside the school, none have assessed whether the noise peaks of fluctuating traffic and exposure to noise inside the classroom could affect children’s cognition.
——What did the researchers do and find?
* We carried out a cohort study to assess whether school exposure (inside and outside classrooms) and home exposure to road traffic noise were associated with the development of working memory and attention over 12 months in 2,680 children aged 7 to 10 years from 38 schools in Barcelona, Spain.
* We assessed long-term exposure to road traffic noise outside and inside the school with measurements (average noise levels and noise fluctuation) and at home with Barcelona’s noise map (outdoor average noise levels).
* We used computerised tests every 3 months over 12 months to measure the development of working memory (the system that keeps and manipulates transitory information), complex working memory (it further involves continuous updating of the working memory), and inattentiveness in children.
* We observed that higher exposure to road traffic noise outside and inside the school, but not at home, was associated with a slower development of working memory and a slower improvement of inattentiveness over 12 months. Inside the classroom, associations were more evident for exposure to noise fluctuation than to average noise levels.
What do these findings mean?
* These findings suggest that, in children aged 7 to 10 years in Barcelona, higher exposure to road traffic noise at school relates to poorer development of attention and working memory. These are important for learning.
* The findings might not be applicable to other populations and need replication in other locations.
* These findings are of public health relevance given the large number of children exposed to road traffic noise in schools and support the implementation of environmental noise policies that protect the school environment.