Air pollution linked to hospital admissions for mental health, study suggests

Air pollution has been linked to increased risks of hospital admission for mental health, as well as physical illness, research found.

Scientists at the University of St Andrews revealed that cumulative exposure to air pollution is linked to a heightened risk of admission to hospital for mental and physical conditions.

Previous research has focused on deaths rather than hospital admissions, and physical health, rather than mental health, according to the team – however, analysis of data tracked from Public Health Scotland examined four key pollutants between 2002 and 2017 and the impact of “ambient” air pollution.

Dr Mary Abed Al Ahad, from the School of Geography and Sustainable Development, led the data review on the health effects of long term exposure, and concluded stricter environmental restrictions are needed to curb the impact on secondary care.

Researchers drew on individual level data from the Scottish Longitudinal Study, which represents 5% of the Scottish population and includes demographic information from linked censuses.

In all, 202,237 people aged 17 and above were included in the research which was published in the open access journal BMJ Open using data from 16 years.

Their health and hospital admissions for cardiovascular, respiratory, or infectious diseases and mental illness/behaviour disorders, were tracked from Public Health Scotland data and linked to levels of four pollutants from road traffic and industry – nitrogen dioxide (NO2); sulphur dioxide (SO2); particulate matter diameter of at least 10 μm (PM10); and small particulate matter of 2.5 μm or less (PM2.5) per 1 km2 in each person’s residential postcode.

Fluctuations in pollutant levels were observed across the study period, with higher levels recorded in 2002–04.

Over the entire period, average levels of NO2, SO2, PM10 and PM2.5 were 12, 2, just above 11, and just above 7 μg/m3, respectively.

The average annual levels for NO2, PM10 and PM2.5 were lower than the 2005 World Health Organisation (WHO) guidelines but the levels of NO2 and PM2.5 were higher than the most recent 2021 WHO guidelines.

Average cumulative exposure to air pollution was strongly associated with higher rates of hospital admissions.

Higher cumulative exposure to NO2, PM10, and PM2.5 was associated with a higher incidence of hospital admissions for all causes, and for cardiovascular, respiratory, and infectious diseases before accounting for residential area.

When fully adjusted for cumulative exposure across time, the incidence rate for respiratory disease hospital admissions rose by just above 4% and just above 1%, respectively, for every 1 μg/m3 increase in PM2.5 and NO2 pollutants.

Sulphur dioxide was mainly associated with hospital admissions for respiratory disease while nitrogen dioxide was associated with a higher number of hospital admissions for mental illness/behavioural disorders.

Exposure to ambient air pollution was assessed yearly rather than monthly or daily, so masking seasonal variations, while residential postcode had to serve as a proxy for personal exposure to air pollution.

Dr Mary Abed Al Ahad said “Policies and interventions on air pollution through stricter environmental regulations, long term planning, and the shifting towards renewable energy could eventually help ease the hospital care burden in Scotland in the long term.

“Policies and interventions targeting air pollution emissions such as zero-emission zones or incentives for renewable energy in transportation and energy production sectors could help ease the hospital-care burden in the long-term both locally and globally.”