Exposure to relatively high levels of air pollution is directly linked to increased use of community mental health services by people with dementia, reveals a long-term study focusing on a large, heavily trafficked area of London, published in the journal 'BMJ Mental Health'.
The researchers suggest that lowering levels of nitrogen dioxide and particulate matter could reduce demand in urban areas and help free up resources in overburdened psychiatric services.
Many studies have focused on the effects of air pollution in old age, including its possible role in accelerating cognitive decline and dementia, they add.
But while pollution has been linked to increased use of healthcare services by people with dementia, these studies have focused primarily on hospital services, rather than community services, which is where the majority are cared for. of people with this disease in the UK.
The researchers looked at the nine-year use of community mental health services by 5,024 older people (aged 65 and over) living in four south London boroughs after receiving an initial diagnosis of dementia between 2008 and 2012.
More than half (54%, 2,718) had been diagnosed with Alzheimer's disease, caused by deposits of plaques and tangles in the brain; one fifth (20%, 1,022) had vascular dementia, caused by damage to the blood vessels in the brain; and more than a quarter (26.5%, 1,330) had another type of dementia or unspecified dementia.
Published quarterly estimates of two major air pollutants, nitrogen dioxide (NO2) and particulate matter (PM2.5 and PM10), in the area surrounding participants' homes were linked to their anonymous mental health histories during the period 2008-12.
Exposure to all air pollutants was higher in people with vascular dementia and lower in those with Alzheimer's disease. The follow-up period was divided into three moments: up to 12 months, up to 5 years, and up to 9 years after diagnosis.
In the first year of follow-up, increased exposure to all air pollutants was associated with increased use of community mental health services by people with dementia, after accounting for potentially influencing factors.
The higher the level of exposure, the greater the use of these services, especially in the case of NO2 exposure. This was especially notable among people with vascular dementia.
Compared with those living in areas with the lowest NO2 exposure levels, those living in areas with the highest level of exposure were 27% more likely to use these services. And those exposed to the highest levels of very small particles (PM2.5) were 33% more likely to use mental health services.
The relationship between PM2.5 and more frequent use of mental health services was still evident 5 and 9 years later for people with Alzheimer's disease and vascular dementia, but was more evident for people 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+) to measure physical health and social activity.
At all time points, NO2 exposure was associated with higher HoNOS65+ scores, indicating poorer health and social functioning, including ability for routine activities of daily living, but not worse cognition.. Similar results were obtained for the particles.
Air pollution was not associated with brain function as measured by MMSE scores during the study period.. However, NO2 exposure was associated with higher HoNOS65+ scores at all time points, indicating poorer social and health functioning, including the ability to perform activities of daily living.. The results were similar in the case of PM2.5.
This is an observational study, so firm conclusions about the cause-effect relationship cannot be drawn.. The researchers also acknowledge that they were unable to assess the impact of exposure to pollutants early in life, fluctuations in exposure over 9 years, or changes in exposure due to residential mobility or time away from home.
However, based on their findings, they estimate that if annual PM2.5 exposure in London (11.6 micrograms/m3 in 2019) were to drop to 5 micrograms/m3, as recommended by the World Health Organization, the number of contacts of people with dementia with community mental health services could be reduced by 13% per year.
Similarly, reducing annual NO2 levels (39 micrograms/m3 in 2019) to the recommended limit of 10 micrograms/m3 could reduce annual contacts with mental health services by 38%.. These estimates could be applied to other large cities in high-income countries with heavy diesel traffic, they suggest.
“Based on the evidence presented, we argue that air pollution could be considered an important population-level target for reducing the use of mental health services in people with dementia, particularly for those with vascular dementia,” they write.
They add: “Reducing air pollution, and in particular NO2, through public health interventions such as expanding ultra-low emission zones could potentially improve the functioning and disease trajectories of people with dementia.”. “Reducing exposure to pollutants could reduce the use of mental health services in people with dementia, freeing up resources in already heavily stretched psychiatric services,” he concludes.