Cardiovascular Disease and Long-term Exposure to Air Pollution Associated with Dementia Risk

by | Aug 18, 2020 | 2020, Brain Health, Cardiovascular Health, Environmental Health, Pollution

Written by Joyce Smith, BS. This study found an increased association between exposure to higher levels of air pollution and dementia, with cardiovascular disease and stroke strengthened the association during the last five years of exposure.

This study attempts to clarify whether cardiovascular disease is an active player in the association between long term exposure to air pollution and dementia. Air pollution has well-established repercussions on human health, especially pulmonary and cardiovascular diseases and dementia. With a worldwide aging population, dementia is expected to triple within the next 30 years, creating a global need for preventative strategies. While research has included predisposing factors such as lifestyle, drugs, and health conditions 1, evolving evidence is suggesting that air pollution, excessive oxidative stress, neuroinflammation, neurodegeneration and inflammation 2 may all be linked to the increasing levels of air pollution and brain pathology 3,4. A 2019 Canadian study suggested that CVD mediated the potential association between dementia and high levels of PM2.5 and NO2 air pollution and concluded that improved cardiovascular health may prevent dementia in areas of higher exposure to air pollution 5.

To investigate further the association between long-term exposure to air pollution and dementia and to assess the role of CVD in that association, Grande and colleagues 6 analyzed data from a longitudinal population-based cohort study in Sweden, the 2001-2013 Swedish National Study on Aging and Care in Kungsholmen (SNAC-K). Baseline assessments were carried out on 3,363 assessed participants, aged 60 and older, from March 21, 2001 through August 30, 2004. The 2,927 dementia-free participants, 1,845 (63.0%) female, were followed up to year 2013 and data analyzed from June 2018 – 2019. Using stratified analyses and generalized structural equation modeling, the team investigated whether CVD (atrial fibrillation, ischemic heart disease, heart failure, and stroke) could modify or strengthen the association between long-term exposure to air pollution and dementia.

Mean concentrations of two major residential outdoor air pollutants (particulate matter ≤2.5 μm [PM] and nitrogen oxide [NO2]) were assessed yearly from 1990 to completion of study (≈21 years) for the cohort participants, using dispersion models for outdoor levels at residential addresses. During the 5 years preceding the study, mean level for PM2.5 was 8.4 μg/m and 25.9 μg/m  for NO2, while in the 6 to 11 years preceding the event, these levels were higher (8.6 μg/m and 33.3 μg/m , respectively).

During the follow-up, 364 incident cases of dementia were identified. Dementia were more prevalent in women, (263; 72.3%) particularly those with less education (294; 81.9%) and who were a mean of 10.3 (95% CI, 9.1-11.4) years older at baseline than those who never developed dementia (P < .05). An increased association between exposure to higher air pollution levels (MP2.5 and NO2) and dementia was found during the last 5 years of exposure. During that time, the hazard of dementia increased by as much as 50% per interquartile range difference in mean pollutant levels at the residential addresses.

Also, the association was stronger in spite of the fact that exposure levels were comparatively low in Kungsholmen, Sweden during that time. Heart failure and ischemic heart disease strengthened the dementia risk while stroke (preceding dementia onset) appeared to be the most important intermediate condition, explaining 49.4% of air pollution-related dementia cases.

Although researchers were able to establish harmful effects of air pollution in Sweden where air pollution levels were lower than current standards, the mechanisms through which air pollution affects brain health are not well understood. They suggest that ultrafine air particulates may enter the brain viathe blood circulation, causing systemic inflammation, blood-brain barrier damage, microglia activation, ultrafine particulate deposition, and accumulation of amyloid beta-42 and alpha-synuclein 7.

The geographical area covered in this study was urban and included just a portion of the city of Stockholm. Only residential addresses were included in assessing exposure and did not provide a true representation of air pollution exposure. Since almost all of the association of air pollution with dementia appeared to occur through the presence or development of CVD, controlling the risk factors for CVD may be a beneficial intervention for people living in highly polluted areas.

Source: Grande, Giulia, Petter LS Ljungman, Kristina Eneroth, Tom Bellander, and Debora Rizzuto. “Association between Cardiovascular Disease and Long-term Exposure to Air Pollution with the Risk of Dementia.” JAMA neurology (2020).

Copyright 2020 Grande G et al. JAMA Neurology. This is an open access article distributed under the terms of the CC-BY License.

Click here to read the full text study.

Posted August 18, 2020.

Joyce Smith, BS, is a degreed laboratory technologist. She received her bachelor of arts with a major in Chemistry and a minor in Biology from  the University of Saskatchewan and her internship through the University of Saskatchewan College of Medicine and the Royal University Hospital in Saskatoon, Saskatchewan. She currently resides in Bloomingdale, IL.

References:

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