Air pollution
According to a recent Lancet commission on pollution and health, pollution is the largest environmental cause of disease and premature death in the world today, responsible for an estimated 16% of all deaths worldwide and associated with a much wider range of disease than was previously thought [1]. Air pollution in particular is at highest concentration in Low and Middle-Income Countries (LMIC) but can disperse globally and has a disproportionally greater effect on the vulnerable, children and older adults [1].
Dementia
The risk of dementia, and the cognitive decline that precedes it, rise with increasing age. The globally ageing population means that the absolute numbers of those living with dementia continue to increase with an estimated new case every three seconds [12]. The rise in dementia cases is global but due to differing patterns in risk factor exposure and healthcare access, the rise is greater in LMIC [12].
Air pollution and dementia
Exposure to air pollution, especially fine particulate matter, is thought to increase risk of hypertension, raised lipids, atherosclerosis, oxidative stress, insulin resistance, endothelial dysfunction, enhanced propensity toward coagulation, inflammation, and stroke, all of which also raise risk of cognitive decline and dementia [1–4, 13–17].
The 2017 Lancet commission on dementia prevention, intervention and care included air pollution in a list of potential risk factors for dementia [18]; the 2018 Lancet commission on pollution states that the evidence of causation is building, in particular for fine particulate matter and dementia in the elderly, and it calls for research to explore emerging causal links [1]. Given that air pollution is known to have a negative effect on human health, a clinical trial of the length needed to evaluate effect on cognitive function is unlikely and the best evidence to demonstrate a causal link will come from longitudinal observational studies. Recent interest in this area has led to the publication of several such studies examining air pollution exposure and incident cognitive decline or dementia [6, 11].
Our aim was to systematically review the evidence base with respect to the relationship between air pollution and incident cognitive decline and dementia in adult populations and to update our earlier review in this area [11]. The protocol for this review is registered with the International prospective register of systematic reviews (http://www.crd.york.ac.uk/prospero/) no. CRD42018094299 and is an update of an earlier review CRD42014007582 [12]
Results:
From 3,720 records, 13 papers were found to be relevant, with studies from the USA, Canada, Taiwan, Sweden, and the UK. Study follow-up ranged from one to 15 years. Pollutants examined included particulate matter ≤2.5 μ (PM2.5), nitrogen dioxide (NO2), nitrous oxides (NOx), carbon monoxide (CO), and ozone. Studies varied in their methodology, population selection, assessment of exposure to pollution, and method of cognitive testing. Greater exposure to PM2.5, NO2/NOx, and CO were all associated with increased risk of dementia. The evidence for air pollutant exposure and cognitive decline was more equivocal.
Conclusion:
Evidence is emerging that greater exposure to airborne pollutants is associated with increased risk of dementia.
Ref
. 2019 Aug 13;70(Suppl 1):S145–S163. doi: 10.3233/JAD-180631
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