Air Pollution in London is Associated with Increased Risk of Dementia

Written by Joyce Smith, BS. Study finds that older residents of London living in areas with higher air pollution were more likely to be diagnosed with dementia in subsequent years compared to those living in areas of lower air pollution.

Dementia, including both Alzheimer’s disease and vascular dementia, represent 12% of the leading causes of death in England and Wales and the 5^th leading cause of death based on the Global Burden of Disease ranking ¹, thus making prevention of all dementia an important global health concern ². The Global Burden of Disease studies have definitively established air pollution as a risk factor for cardiovascular and respiratory diseases and, as well, have shown the worldwide impact of air pollution on the prevalence of stroke, lung cancer, and chronic obstructive pulmonary disease ³. Some studies investigating neurological outcomes have linked living near major roads with the development of  Parkinson’s disease and Multiple Sclerosis ⁴, while others have suggested a genetic susceptibility to neurological effects of air pollution in later life ⁵. There is also evidence that brain development in children may be affected by traffic sources such as lead in gasoline ⁶. Early air pollution exposure in young children has been linked to impaired cognitive development ⁷ and when continued long-term, may  produce neuroinflammation and an altered brain innate immune response that disrupts the blood brain barrier and promotes the accumulation of amyloid beta-42 and alpha- synuclein in both children and young adults ⁸.

This study ⁹ was a retrospective observational study that used primary care data to investigate a potential association between dementia incidence and the residential levels of air and noise pollution in London. Carey and colleagues examined data from existing electronic health records of 130,978 older adults, ages 50 to 79, who were registered between 2005 and 2013 with 75 primary care practices located within the London orbital M25 motorway. Patients had no recorded history of dementia or of requiring home care. Based on their residential postcodes, the research team estimated the patients’ yearly exposure to air pollutants and their proximity to heavy traffic and road noise using fine resolution modeling methods validated with recorded measurements. Road traffic noise levels were estimated using the TRAffic Noise EXposure (TRANEX) model ¹⁰. The pollutants of interest were nitrogen dioxide, fine particulate matter, and ozone.

Researchers found that based on an average of 7 years, 2,181 patients (1.7%) were diagnosed with dementia, of which 39% were Alzheimer’s disease and 29% were vascular dementia. There was an association between dementia and all measures of air pollution except ozone.  Adults living in areas in the top fifth of nitrogen dioxide concentration (>41.5 µg/m3) versus the lowest fifth (<31.9 µg/m3) had an increased risk of dementia (HR 1.40). The researchers also saw increases in dementia risk with fine particulate matter from primary traffic sources and night-time noise levels, but only nitrogen dioxide and fine particulate matter remained statistically significant in multi-pollutant models. Associations were more consistent for Alzheimer’s disease than vascular dementia.

These results suggest that both regional and urban background pollutants may be as important as near-traffic pollutants. This London study was able to simultaneously analyze the modelled effects of air and noise pollution on dementia which previous studies could not do; however, it was an observational study which may limit its application to the London area only. Researchers suggest these findings be interpreted with caution since more research is needed to confirm an association between air pollution and dementia. They recommend future large-scale studies that provide improved recording and linkage of dementia diagnoses across electronic systems to improve diagnostic accuracy, particularly with respect to Alzheimer’s disease

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).

This is an open access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license http:// creative commons. org/ licenses/ by- nc/ 4. 0/

Posted July 28, 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:

1. Newton JN, Briggs AD, Murray CJ, et al. Changes in health in England, with analysis by English regions and areas of deprivation, 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013. Lancet. 2015;386(10010):2257-2274.
2. Prince M. The global prevalence of dementia: a systematic review and metaanalysis. Alzheimer’s & dementia. 2013;no. 1:63-75.
3. Cohen AJ, Brauer M, Burnett R, et al. Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study 2015. The Lancet. 2017;389(10082):1907-1918.
4. Chen H, Kwong JC, Copes R, et al. Living near major roads and the incidence of dementia, Parkinson’s disease, and multiple sclerosis: a population-based cohort study. Lancet. 2017;389(10070):718-726.
5. Bakulski KM, Rozek LS, Dolinoy DC, Paulson HL, Hu H. Alzheimer’s disease and environmental exposure to lead: the epidemiologic evidence and potential role of epigenetics. Curr Alzheimer Res. 2012;9(5):563-573.
6. Sunyer J, Esnaola M, Alvarez-Pedrerol M, et al. Association between traffic-related air pollution in schools and cognitive development in primary school children: a prospective cohort study. PLoS Med. 2015;12(3):e1001792.
7. Carey, Iain M., H. Ross Anderson, Richard W. Atkinson, Sean D. Beevers, Derek G. Cook, David P. Strachan, David Dajnak, John Gulliver, and Frank J. Kelly. “Are noise and air pollution related to the incidence of dementia? A cohort study in London, England.” BMJ open 8, no. 9 (2018): e022404.
8. Gulliver J, Morley D, Vienneau D, et al. Development of an open-source road traffic noise model for exposure assessment. Environmental Modelling & Software 2015;74:183–93.