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Air pollution and dementia – link to higher mental health service use

Cutting levels of pollution could help free up overstretched psychiatric resources in urban areas, research suggests

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Exposure to higher levels of air pollution is linked to increased use of community mental health services by people with dementia, a new study has revealed. 

And by cutting levels of nitrogen dioxide (NO2) and particulate matter, this could help free up overstretched psychiatric resources in urban areas, the research suggests. 

The long-term study focused on four boroughs of South London with heavy traffic, and involved 5,024 older people – aged 65 and over – following a dementia diagnosis, between 2008 and 2012. 

“Based on the evidence presented, we contend that air pollution could be considered an important population-level target to reduce mental health service use in people with dementia, particularly for those with vascular dementia,” say the study authors.

“The reduction in air pollution and particularly NO2 through public health interventions, such as the expansion of ultra-low emission zones, could potentially improve functioning and disease trajectories for people with dementia.

“Reducing pollutant exposure might reduce the use of mental health services in people with dementia, freeing up resources in already considerably stretched psychiatric services.”

An estimated 850,000 people are living with dementia in the UK, with the number projected to increase to 2million by 2050, in tandem with the ageing of the population. Dementia is already the leading cause of death in the UK, note the researchers.

Growing numbers of research projects have focused on the effects of air pollution in older age, including its potential role in the speeding up of cognitive decline and dementia, they add.

But while air pollution has been linked to increased health service use by people with dementia, these studies have largely focused on hospital services, rather than community services, which is where most people with the condition are managed in the UK.

In this study of over 5,000 people in a large area of London, over half (54 per cent, 2,718) had been diagnosed with Alzheimer’s disease, which is caused by plaque deposits and tangles in the brain; a fifth (20 per cent,1,022) had vascular dementia, which is caused by damage to blood vessels in the brain; and over a quarter (26.5 per cent,1,330) had other or unspecified dementia.

Quarterly published estimates of two major air pollutants – nitrogen dioxide (NO2) and particulate matter (PM2.5 and PM10) – covering the area around participants’ homes were linked with their anonymised mental health records for the period 2008-12.

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 time points: 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 by people with dementia, after accounting for potentially influential factors.

The higher the level of exposure, the greater the use of these services, particularly for exposure to NO2. This was especially noticeable among those with vascular dementia.

Compared with those living in areas with the lowest levels of exposure to NO2, those living in areas with the highest level of exposure were 27 per cent more likely to use these services.

And those exposed to the highest levels of very small particulate matter (PM2.5) were 33 per cent more likely to use mental health services.

The associations between PM2.5 and more frequent mental health service use were still evident five and nine years later for people with Alzheimer’s disease and vascular dementia, but were most noticeable for those with vascular dementia.

During the study period the Mini Mental State Exam (MMSE) was used to measure brain function and the Health of the Nation Outcomes Scale (HoNOS65+) was used to measure physical health and social activity.

At all time points, exposure to NO2 was associated with higher HoNOS65+ scores, indicating poorer health and social functioning, including the capacity for routine activities of daily living, but not poorer cognition. Similar findings emerged for particulate matter.

Air pollution was not associated with brain function as measured by MMSE results over the study period. But exposure to NO2 was associated with higher HoNOS65+ scores at all time points, indicating poorer health and social functioning, including the capacity for routine activities of daily living. Similar findings emerged for PM2.5.

Based on their findings, the researchers estimate that if the annual PM2.5 exposure 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 per cent 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 per cent.

These estimates are likely to apply to other large cities in high income countries with heavy diesel traffic, they suggest.

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