Almost 70% of the world’s population could be living in urban areas, being continuously exposed to air pollution, by 2050, while cases of dementia are expected to triple. Recent study results highlight the link between cardiovascular disease and dementia, as mediated by long-term exposure to air pollution.
Sixty-eight percent of the world’s population could be living in urban areas, being continuously exposed to air pollution, by 2050, while cases of dementia are expected to triple. Recent study results from a team at the Karolinska Institutet in Stockholm, Sweden, published in JAMA Neurology, highlight the link between cardiovascular disease (CVD)—namely, heart failure, ischemic heart disease, and stroke—and dementia, as mediated by long-term exposure to air pollution levels of particulate matter (<2.5 μm [PM2.5]) and nitrogen oxide (NOX) measured since 1990.
"Air pollution is an established risk factor for cardiovascular health and because CVD accelerates cognitive decline, we believe exposure to air pollution might negatively affect cognition indirectly," stated Giulia Grande, researcher at the Department of Neurobiology, Care Sciences and Society at Karolinska Institutet and first author on the study. "In our study, virtually all of the association of air pollution with dementia seemed to be through the presence or the development of CVD, adding more reason to reduce emissions and optimize treatment of concurrent CVD and related risk factors, particularly for people living in the most polluted areas of our cities.”
Overall results show that heart failure and ischemic heart disease increased the risk of dementia and that stroke was a likely reason behind the development of close to 50% of cases of air pollution—related dementia.
Study participants, who were from the Kungsholmen district of Stockholm, were already enrolled in the ongoing Swedish National Study on Aging and Care in Kungsholmen. Baseline assessments were performed between March 21, 2001, and August 30, 2004, on 2927 participants whose mean (SD) age was 74.1 (10.7) years; none had dementia at the time. Sixty-three percent were female. There was a mean (SD) follow-up of 6.01 (2.56) years by the end of the study period (February 18, 2013).
International Statistical Classification of Disease and Related Health Problems, Tenth Revision, criteria were used to classify the CVDs, and Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, criteria were used to define dementia. Pollution levels were measured at the participants’ residential addresses,and calculated every 5 years (1990, 1995, 2000, 2005, and 2011).
During follow-up, 364 of the study participants developed dementia, the risk of which increased the most per interquartile (IQR) range difference in the previous 5 years for both levels of pollutants measured (HR for difference of 0.88 μm/m3 PM2.5, 1.54 [95% CI, 1.33-1.78]; HR for difference of 8.35 μm/m3 NOX, 1.14 [95% CI, 1.01-1.29]). When heart disease was investigated for its role in dementia development, these numbers were even higher:
As for stroke’s relationship to dementia and pollution, the results showed a 26% greater risk of stroke per IQR difference at higher levels of PM2.5, and the odds of developing dementia were 3.8 times greater following a stroke.
“Cardiovascular disease appeared to amplify the negative association of air pollution. In particular, heart failure and ischemic heart disease seemed to enhance the dementia risk, whereas stroke seemed to be an important condition between air pollution and dementia,” the authors concluded. “Interestingly, the higher [pollution] limit reported herein is not only below the current European limit for fine particulate matter but also below the US standard.”
Grande G, Ljungman PLS, Eneeroth K, Bellander T, Rizzuto D. Association between cardiovascular disease and long-term exposure to air pollution with the risk of dementia [published online March 30, 2020]. JAMA Neurol. doi: 10.1001/jamaneurol.