Genetic, environmental and behavioural risk factors are associated with dementia. But the Lancet Commission on Dementia Prevention, Intervention and Care has now speculated that air pollution is a significant risk factor to consider in public health interventions.

Oudin and colleagues published a study in Nature in June 2024 that quantified the associations between total and distinct source-specific particulate matter (PM) concentrations of ambient air pollution and dementia in Northern Sweden. The rationale behind this research was the lack of a well-executed longitudinal study of the causal relationship between long-term pollution and the incidence of dementia, which accurately accounts for local emission variations in pollution from sources such as car exhaust from traffic and wood burning.

Dementia is a term used to embody a range of neurological conditions characterised by a gradual decline in cognitive abilities, memory, behaviour, problem-solving skills and language. It imposes restrictions on individuals in everyday life and causes an emotional strain on those to whom they are closest. Dementia also contributes to global disease mortality and morbidity.

In the 16 major pharmaceutical markets (16MM: Australia, Brazil, Canada, China, France, Germany, India, Italy, Japan, Mexico, Russia, South Africa, South Korea, Spain, the UK and the US) GlobalData epidemiologists have predicted there will be 43.4 million total prevalent cases of dementia in men and women aged 60 years and over by the end of 2024, and 56.5 million cases by the end of 2032. Due to a lack of current treatment for the condition, more emphasis has been placed on prevention through managing established modifiable risk factors.

In this cohort study, Oudin and colleagues analysed data on 70,057 individuals enrolled in the Vasterbotten Intervention Program between 1990 and 2014, to measure the risk proposed by air pollution on dementia. Individuals with newly diagnosed dementia were identified by ICD-10 codes, and extensive care was taken to exclude prevalent cases. Over the total 884,847 person-years of follow-up, 409 incident cases of dementia were identified. The risk of dementia upon exposure to PM 10 [particulate matter 10 micrometres or less in diameter] from all sources was highest in the lowest tertile [third], where particulate concentration is lowest; the pattern was observed for those with 1 to 5 years of exposure until dementia and 6 to 10 years of exposure until dementia. Similar findings were found for exposure to PM 2.5 from all sources at lower concentrations, which yielded a higher risk of dementia compared to exposure at higher concentrations.

However, when PM 10 exposure from traffic was isolated, researchers found a statistically significant association between 1 to 5 years of prior exposure to PM 10 from traffic air pollution at median concentrations and the risk of dementia, which was increased by 1.43 times compared to exposure at the lowest concentration. This suggests that it is important to consider the source of air pollution and the specific environmental context when assessing the impact of air pollution on dementia risk. 

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The relationship between air pollution and dementia risk appears more complex than initially suspected, and previous studies yielded mixed results. However, this only indicates that more research in this field is needed to understand and account for nuances between air pollution impact based on different environmental conditions and populations to broaden data on this critical public health issue.