Abstract
ObjectivesThere is highly suggestive evidence for an effect of air pollution exposure on dementia-related outcomes, but evidence is not yet present to clearly pinpoint which pollutants are the probable causal agents. The aims of this study was to assess the longitudinal association between exposures of fine ambient particulate matter (PM2.5) from residential wood burning, and vehicle exhaust, with dementia.MethodWe used data from the Betula study, a longitudinal study of dementia in Umeå, Northern Sweden. The study size was 1 806 and the participants were followed from study entry (1993–1995) to 2010. Modelled levels of source-specific fine particulate matter at the residential address were combined with information on wood stoves or wood boilers, and with validated data on dementia diagnosis and individual-level characteristics from the Betula study. Cox proportional hazards models were used to estimate Hazard Ratios (HRs) and their 95% CIs for dementia incidence (vascular dementia and Alzheimer’s disease), adjusted for individual-level characteristics.ResultsThe emission of PM2.5 from local residential wood burning was associated with dementia incidence with a hazard ratio of 1.55 for a 1 μg/m3 increase in PM2.5 (95% Confidence Interval (CI): 1.00–2.41, p-value 0.05). Study participants with an address in an area with the highest quartile of PM2.5 from residential wood burning and who also had a wood-burning stove were more likely to develop dementia than those in the lower three quartiles without a wood-burning stove with hazard ratios of 1.74 (CI: 1.10–2.75, p-value 0.018). Particulate matter from traffic exhaust seemed to be associated with dementia incidence with hazard ratios of 1.66, (CI: 1.16–2.39), p-value 0.006, and 1.41 (CI: 0.97–2.23), p-value 0.07, in the third and fourth quartiles, respectively.ConclusionsIf the associations we observed are causal, then air pollution from residential wood burning, and air pollution from traffic, might be independent important risk factors for dementia.
Highlights
Dementia is a major cause of morbidity and mortality worldwide
Chen and colleagues later showed that living close to heavy traffic was associated with dementia in Canada, with an adjusted hazard ratio (HR) of 1.07 (CI: 1.06– 1.08) for people living less than 50 m from a major traffic road as compared with living further than 300 m[3]
In two early studies from Taiwan, NO2 was correlated with elevated risk of dementia, with a HR of 1.54 (CI: 1.34–1.77) in quartile 4 versus quartile 1[4], and a 4.34 μg/m3 increase in particulate matter 2,5 μm or less in diameter (PM2.5) was associated with an HR of 2.38 (CI: 2.21–2.56) [5]
Summary
Dementia is a major cause of morbidity and mortality worldwide. By 2050, the number of Alzheimer’s Disease (AD) patients is expected to rise to over 130 million from today’s 47 million [1]. In a study from Northern Sweden, we have previously observed residential concentrations of traffic-related air pollution to be a risk factor for vascular dementia and AD, with an attributable fraction of 16% [2]. Chen and colleagues later showed that living close to heavy traffic was associated with dementia in Canada, with an adjusted hazard ratio (HR) of 1.07 (CI: 1.06– 1.08) for people living less than 50 m from a major traffic road as compared with living further than 300 m[3]. In two early studies from Taiwan, NO2 was correlated with elevated risk of dementia, with a HR of 1.54 (CI: 1.34–1.77) in quartile 4 versus quartile 1[4], and a 4.34 μg/m3 increase in particulate matter 2,5 μm or less in diameter (PM2.5) was associated with an HR of 2.38 (CI: 2.21–2.56) [5]. A review from 2016 concludes that it is highly plausible, that air pollution has an effect on cognition, but current evidences does not clearly pinpoint which pollutants are the probable causal agents[7]
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