Traffic-Related Air Pollution and Dementia Incidence in Northern Sweden

This article [ref below] is VERY well written in that the authors’ closing statement starts with:  “If the associations we observed are causal, …”  I suggest virtually all epidemiological publications include this excellent phrase in their summary, and I’m sure that others would agree.

Exposure to ambient air pollution has long been suspected to cause cognitive effects, but a prospective cohort has been needed to study exposure to air pollution at the home address of the subjects as well as the incidence of dementia of these subjects. Authors aimed to assess the association between long-term exposure to traffic-related air pollution and dementia incidence among subjects living in a major city in northern Sweden. Data on the incidence of dementia were obtained over a 15-year period. Traffic air pollution exposure was assessed using a land-use regression model with a spatial resolution of 50 m × 50 m. Annual mean nitrogen oxide levels at the residential address of the participants at baseline (the start of follow-up) were used as markers for long-term exposure to air pollution.

Out of 1,806 participants at baseline, 191 were diagnosed with Alzheimer disease during follow-up, and 111 were diagnosed with vascular dementia. Participants in the group with the highest exposure were more likely than those in the group with the lowest exposure to be diagnosed with dementia (Alzheimer’s disease or vascular dementia), with a hazard ratio (HR) of 1.43 [95%;  CI = 0.998, 2.05] for the highest versus the lowest quartile). The estimates were similar for Alzheimer disease (HR = 1.38) and vascular dementia (HR = 1.47). The HR for dementia associated with the third quartile versus the lowest quartile was 1.48 [95%; CI = 1.03, 2.11]. A subanalysis that excluded a younger sample that had been re-tested after only 5 years of follow-up suggested stronger associations with exposure than were present in the full cohort [HR = 1.71; (95% CI = 1.08, 2.73) for the highest vs lowest quartile).

Authors conclude that:  “If the associations we observed are causal,” … then air pollution from traffic might be an important risk factor for vascular dementia and Alzheimer disease. NB:  When confidence interval (CI) values overlap and include values below 1.00, … some of us always get a bit nervous.

 Environ Health Perspect  Mar 2o16; 124: 306–312

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