London researchers say tackling air pollution 'could ease pressure on mental health services'
A team from King's College have been studying patients living in four boroughs of south London.
The number of people with vascular dementia using community mental health services could be reduced if levels of air pollution are cut, researchers have suggested.
A team from King's College London looked at community mental health service use over nine years by 5,024 people aged 65 and over.
All patients lived in four boroughs of south London - Croydon, Lambeth, Lewisham or Southwark - following their initial dementia diagnosis between 2008 and 2012.
More than half of those involved had Alzheimer's disease (54%), 20% had vascular dementia, and 26.5% had unspecified dementia.
Vascular dementia is caused when there are issues with the blood supply to the brain and can be caused by high blood pressure, stroke or heart problems.
The study, published in medical journal BMJ Mental Health, measured cognitive function and health and social functioning at three points in time - up to 12 months after diagnosis, up to five years after diagnosis, and up to nine years after diagnosis.
They then looked at quarterly published estimates for two major air pollutants - nitrogen dioxide (NO2) and particulate matter - covering the areas around the patients' homes during the same timeframe.
In the first year, higher exposure to both air pollutants was associated with an increase in use of community mental health services by people with dementia.
The researchers said: "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."
Those in areas with higher levels of NO2 were 27% more likely to use community mental health services than those living in areas with the lowest levels, while those exposed to the highest levels of particulate matters were 33% more likely to use them.
Researchers said that while air pollution was not associated with cognitive function based on the scale they used, exposure to NO2 was associated with poorer health and social functioning scores, including the capacity for routine and daily living.
They added that, as the study was observational, "no firm conclusions can be drawn about cause and effect".
However, they suggested that if the annual level of exposure to inhalable particulate matter in London was reduced, as recommended by the World Health Organisation (WHO), the number of community mental health service contacts made by patients with dementia could fall by 13%.
"These estimates are likely to apply to other large cities in high-income countries with heavy diesel traffic," researchers said.
The team added: "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."
Dr Susan Mitchell, head of policy at charity Alzheimer's Research UK, said the Government is "dragging its feet" when it comes to implementing stricter air quality standards, and that changes could be "a decade too late".
She added: "If this Government is serious about improving lifelong health and reducing the burden on our NHS, it can't continue to turn a blind eye to air pollution.
"Poor air quality is a significant public health issue, and this new research demonstrates its knock-on effect on already over-stretched health services and the lives of people living with dementia.
"As well as urgent action to bring levels down, there is a pressing need to find out more about exactly how air pollution affects dementia risk. This evidence will allow Government and policymakers to develop policies that can reduce the impact of air pollution exposure on people at risk of developing dementia, and those living with the condition."