Associations between long-term exposure to ambient air pollution and Parkinson's disease prevalence: A cross-sectional study
Introduction
Parkinson's disease (PD) is a progressive and disabling neurodegenerative disorder, which, after Alzheimer's disease, is the most common neurodegenerative disorder (De Lau and Breteler, 2006; Jankovic, 2008). The incidence of PD is low before 50 years of age, after which it increases sharply prior to peaking above 80 years of age (Kalia and Lang, 2015). Meta-analyses of world-wide data showed a prevalence of 1,903 PD cases per 100,000 persons older than 80 years (Pringsheim et al., 2014). Studies have found evidence of a greater incidence and prevalence of PD in men compared with women (De Lau and Breteler, 2006).
A meta-analysis of the risk factors for PD found lower risk of PD in smokers, with a 40% lower risk in ever smokers (Noyce et al., 2012). However, it is unclear whether the association is causal and what biological mechanisms may be involved (Ritz and Rhodes, 2010). Apart from age and smoking, the aetiology of PD is still largely unknown, however, emerging evidence suggests that the interplay between genetic and environmental factors may contribute to the development of PD (Kalia and Lang, 2015).
Air pollution, particularly particulate matter (PM), has been implicated as a chronic source of neuroinflammation and reactive oxygen species that may lead to neurological dysfunction (Block and Calderón-Garcidueñas, 2009; Genc et al., 2012). Studies that have assessed the associations between long-term exposure to air pollution and PD have shown inconsistent findings (Cerza et al., 2018; Chen et al., 2017b, Chen et al., 2017a; H Chen et al., 2017a; Finkelstein and Jerrett, 2007; Kioumourtzoglou et al., 2015; Lee et al., 2016; Liu et al., 2016; Palacios et al., 2014a; Palacios et al. 2014b; Palacios et al. 2017; Ritz et al., 2016; Shin et al., 2018).
A recent systematic review and meta-analysis has been conducted on the associations of PD with long-term exposure to air pollution (Kasdagli et al., 2019). They found suggestive associations between long-term exposure to PM2.5 (Relative risk (RR) = 1.06 (95% CI: 0.99–1.14) per 10 increase) and NO2 (RR = 1.01 (95% CI 0.98–1.03) per 10 increase) with PD. They also concluded that further research is required to elaborate their findings. Therefore, this study aimed to examine the association between exposure to ambient PM2.5 and NO2 and the risk of PD using the baseline data from an established cohort of more than 265,000 people aged 45 years and older living in New South Wales (NSW), Australia.
Section snippets
Study population
We conducted a cross-sectional analysis using data from the Sax Institute's ‘45 and Up Study’, described in detail elsewhere (45 and Up Study Collaborators, 2008). Briefly, the 45 and Up Study was established by the Sax Institute and during 2006–2009 recruited 267,153 adults aged 45 years and over in NSW, Australia. Participants were sampled from the Australia's Department of Human Services (formerly Medicare Australia) enrolment database. At recruitment, participants in rural and regional
Results
Of the 266,969 participants residing in the areas with available PM2.5 and NO2 exposure estimates, 30,579 (11%) were excluded due to missing information on outcome and/or covariates. Of the 236,390 remaining participants, 1,428 (0.6%) reported physician-diagnosed PD. PD cases were more likely to be older, male, to have not completed high school, and were more likely to have a family history of PD (Table 1).
PM2.5 and NO2 concentrations were relatively low (Table 2). Mean PM2.5 and NO2
Discussion
In this study, we found positive, but not statistically significant associations between exposure to low level PM2.5 and NO2 and self-reported physician-diagnosed PD. The associations with NO2 was statistically significant in past smokers while no such associations were found in current and non-smokers.
Studies that have examined the associations between long-term exposure to PM10, PM2.5 and NO2 and PD are summarised in Table 6. Nine of 11 studies found positive associations with five results
Conclusions
In summary, we found limited evidence for associations between exposures to NO2 or PM2.5 and PD. The associations with NO2 was stronger and statistically significant in past smokers which warrants further investigation on the modifying effects of smoking.
Acknowledgements
This research was completed using data collected for the 45 and Up Study (www.saxinstitute.org.au). The 45 and Up Study is managed by the Sax Institute in collaboration with major partner Cancer Council NSW; and partners: The National Heart Foundation of Australia (NSW Division); NSW Ministry of Health; NSW Government Family & Community Services – Ageing, Carers and the Disability Council NSW; and the Australian Red Cross Blood Service. We thank the many thousands of people participating in the
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