Jannette Rodríguez Pallares
"Parkinson’s disease is currently the fastest-growing neurodegenerative disorder. According to the World Health Organisation (WHO), the number of cases of Parkinson’s has doubled over the last 25 years, and the organisation warns that this figure could triple over the next 25 years. As the cause of this disease is not yet known, it is of great importance to identify and minimise the risk factors associated with Parkinson’s.
There is considerable evidence linking exposure to certain environmental agents – particularly pesticides used in agriculture and, more recently, industrial pollutants – with an increased risk of developing Parkinson’s disease. Against this backdrop, the study explores whether exposure to road traffic noise might also be associated with this risk, reinforcing the importance of investigating potentially modifiable environmental factors that could contribute to the prevention of the disease.
This is one of the first studies to analyse the role of road traffic noise as a risk factor for Parkinson’s disease. The results indicate that prolonged exposure to traffic noise increases the risk of developing the disease. Compared with previous studies carried out in the Netherlands and Canada, this study, conducted in Denmark, goes a step further, as it includes data from a large number of participants – more than three million people – and takes into account the possible influence of additional variables, including demographic, socio-economic and environmental factors.
The study indicates that exposure of residential building façades to road traffic noise is associated with an increased risk of developing Parkinson's disease. It also suggests that noise may have a particularly important impact during periods of rest, especially in homes that lack a quieter façade, where bedrooms and other resting areas are typically located. These findings highlight the importance of considering such factors in urban planning.
Although the study does not investigate the biological mechanisms that might link noise exposure to the degeneration of dopaminergic neurons characteristic of Parkinson's disease, it suggests that this association could be related to sleep disruption and disturbances of the circadian rhythm. We now know that during sleep, the brain activates systems that help clear toxic molecules, thereby maintaining brain health, and that these processes are disrupted when sleep is fragmented. In addition, noise exposure may contribute to increased inflammation and oxidative stress, both within and outside the nervous system, which are key processes involved in the development of Parkinson's disease. Although it is unlikely that noise directly causes the death of dopaminergic neurons, it may impair the brain's protective mechanisms and promote biological processes involved in disease development. Therefore, further studies are needed to better understand the biological mechanisms that could explain the association between noise exposure and Parkinson's disease. At the same time, additional epidemiological studies will be essential to confirm these findings, identify new risk factors, and provide the evidence needed to inform prevention strategies and guide public health decision-making in light of the growing impact that Parkinson's disease is expected to have in the coming decades.
Is the study of good quality?
“The study has been published in a highly prestigious international medical journal, which follows a rigorous, high-quality peer-review process, thereby supporting the scientific rigour of the methodology and the results described.”
Are there any limitations that need to be taken into account?
“This is a long-term longitudinal study, which includes data from a large number of participants, employs a validated methodology and analyses various demographic, socio-economic and environmental variables, combined with exposure to road traffic noise. However, it does have some limitations, which the authors also acknowledge, such as the need to take into account other indicators, including the structural aspects of housing, participants’ exposure to noise outside the home – for example, in the workplace – or lifestyle factors such as smoking or physical exercise. It would also be interesting to consider other factors that may influence the risk of developing the disease, such as the presence of other health conditions among participants, including obesity, diabetes or high blood pressure. We now know that these conditions increase the risk of developing the disease and could influence the results of this type of study.”
What are the implications of this result, and how does it fit in with the existing evidence? Is traffic noise a new risk factor?
“Whilst exposure to certain environmental factors, such as pesticides, is a well-known risk factor for Parkinson’s disease, the evidence pointing to traffic noise as a possible risk factor is much more recent. Until now, only two previous studies had been published, one using data from the Dutch population and the other from Canada, with conflicting results, partly explained by the methodology and type of study. This is therefore a promising line of research, although it is still at an early stage. Studies such as this one can help to identify modifiable factors which, once confirmed, will contribute to the design of strategies to prevent or reduce the risk of developing the disease.”