The study was published in the open access journal BMJ Mental Health and part-funded by the NIHR Maudsley Biomedical Research Centre and supported by the NIHR Applied Research Collaboration South London.

The research group, led by academics at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) and ESRC Centre for Society and Mental Health at King’s College London, analysed data on 5,024 people with a primary diagnosis of dementia for up to nine years. They used a state-of-the-art air quality model to estimate address-level exposure to pollutants in Southwark, Lambeth, Lewisham, and Croydon.

Over half (54%) had been diagnosed with Alzheimer’s disease, which is caused by plaque deposits and tangles in the brain; a fifth (20%) had vascular dementia, which is caused by damage to blood vessels in the brain; and over a quarter (26.5%) had other or unspecified dementia.

In this new study, researchers linked concentrations of two major air pollutants—nitrogen dioxide (NO₂) and particulate matter (PM_2.5 and PM₁₀) - with anonymised electronic mental health records of community mental health service use. Air pollution exposure was estimated by modelling levels of pollutants at the residential address of the participants at 20 x 20 metre grid points from 2008 to 2012.

The study showed that living at an address with exposure to higher levels of both PM_2.5 (particulate matter consisting of a huge variety of chemical compounds and materials) and nitrogen dioxide (NO₂) was associated with increased use of community mental health services among people with dementia. The reason for use of mental health services varied and included presence of depression, psychosis and behavioural problems linked to dementia.

Exposure to all air pollutants was highest in people with vascular dementia and lowest in those with Alzheimer’s disease.

The monitoring period was divided into three periods (up to 12 months; up to five years and up to nine years after diagnosis). In the first year of monitoring, higher exposure to all air pollutants was associated with an increase in the use of community mental health services in people with dementia.

The higher the level of exposure, the greater the use of these services for people with dementia, particularly for exposure to NO₂ and particularly for people with vascular dementia.

Those living in areas with the highest level of exposure to NO₂ were 27 per cent more likely to use these services compared with those living in areas with the lowest levels of exposure to NO₂. Those exposed to the highest level of very small particulate matter (PM_2.5) were 33 per cent more likely to use community mental health services. These associations were still evident five and nine years later.

The Mini Mental State Exam (MMSE) was used to measure cognitive function and the Health of the Nation Outcomes Scale (HONOS65+) was used to measure physical health and social activity over the study period.

Air pollution was not associated with cognitive function over the study period but exposure to NO₂ was associated with higher HoNOS65+ scores at all time points, indicating poorer health and social functioning. Similar findings emerged for very small particulate matter.

Dr Amy Ronaldson, Research Fellow at King's IoPPN, and first author, said, “Our study showed that there were stronger associations for patients with vascular dementia, which is caused by reduced blood flow to the brain, and implies that air pollution might impact the development of vascular dementia more than other dementia types.

“We looked at associations between air pollution and cognitive function over time, as well as physical health and social functioning. The results of the study indicate that NO₂ exposure negatively impacts health and social functioning more so than cognitive function, which might partially explain how air pollution leads to more use of community mental health teams in people with dementia.”

 

Dr Ioannis Bakolis, Reader in Biostatistics and Epidemiology, at King’s IoPPN, and the study’s senior author said, “Our findings indicate that reducing levels of air pollution could lead to a considerable reduction in the use of community mental health services by people with dementia both in South London as well as other urban traffic areas in the UK. More work is needed to understand how air pollution impacts other aspects of dementia-related care, as well as the pathways involved but our work suggests that urban measures to reduce air pollution could help ease some of the demand on mental health services. We estimate that if the annual PM2.5exposure in London (11.6 µg/m3 in 2019) fell to 5 µg/m3, as recommended by the World Health Organization, the number of community mental health service contacts by people with dementia could be reduced by 13% a year. Similarly, reducing annual levels of NO2 (39 µg/m3 in 2019) to the recommended limit of 10 µg/m3 could reduce annual mental health service contacts by 38%.” 

The researchers used the Clinical Record Interactive Search system (CRIS), a computer system that allows researchers at the NIHR Maudsley Biomedical Research Centre (BRC) to carry out research using information from South London and Maudsley NHS Foundation Trust clinical records.

Associations between air pollution and mental health service use in dementia: A retrospective cohort study, BMJ Mental Health, Amy Ronaldson, Robert Stewart, Christoph Mueller, Jayati Das-Munshi, Joanne B. Newbury, Ian Mudway, Matthew Broadbent, Helen L. Fisher, Sean Beevers, David Dajnak, Matthew Hotopf, Stephani L. Hatch, Ioannis Bakolis. DOI 10.1136/bmjment-2023-300762 

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