Air pollution and mental health: an unhealthy love story
I live in Camberwell, in South East London, just a few minutes away from the Institute of Psychiatry, Psychology and Neuroscience where I currently work.
A typical morning of my everyday commute would be to walk 20 minutes from my house to my son’s school and then another 20 minutes to my office. During my commute, I usually pass from four major roads, a bunch of leafy streets, two parks, a series of big estate buildings, a vibrant high street full of cafes and restaurants, construction sites and a small street full of Georgian houses before I arrive at my office.
During my commute, there are few days especially in the springtime that I am thinking if and how the air I breathe is affecting my mental health and wellbeing … always with a little help from Bo Diddley, Herbert Leroy Needleman, General Motors, the Great London smog and my current research.
“Pollution in the home
Pollution in the streets
Pollution everywhereGonna get you and me
Pollution”- Bo Diddley, Another Dimension (Chess; 1971)
At the same time that Bo Diddley (1928–2008) recorded “Pollution” in the early 1970s, Herbert Leroy Needleman (1927–2017) was about to embark to a seminal epidemiological study — the study of patterns and determinants of health and disease in defined populations — which showed the first link between children being highly exposed to lead from petrol derived from car engines and deficits in their psychologic and classroom performance in Chelsea and Somerville in Massachusetts, USA.
Before Needleman’s study, there were few anecdotal accounts of lead poisoning, spanning from Roman times (a roman physician noted that “lead makes the mind give away”) to the ban of lead coils in rum in the Americas in the 18th century. However, the well-known neurotoxic effects of lead did not stop big industries such as General Motors to include lead as an additive in petrol in the early 1920s and making huge efforts to discredit Needleman’s work.
The effects of these actions on the atmosphere and population health were profound at a global scale for the years to come.
Primary air pollutants are typically released from ‘mobile’ sources (e.g., exhaust fumes from vehicles), ‘stationary’ sources (e.g., emissions from factories) and domestic activities (e.g., coal and wood for cooking and heating).
Secondary air pollutants formed in the atmosphere through chemical reactions.
Thus, traffic is not the only source of poor outdoor air quality, but it is the main driver for air pollution, specifically in cities.
Children are particularly susceptible to harmful effects of traffic-related air pollution, because of central nervous system plasticity during early stages in life.
In 1999, leaded petrol was finally banned in the UK to protect children’s brains from its damaging effects. However, studies continued to emerge linking children residing in areas with poor air quality with deficits in classroom performance and educational attainment. This mounting evidence is due to other components of traffic-related air pollution particles, including carbon monoxide, polycyclic aromatic hydrocarbons and nitrogen dioxides, which have also been shown to be neurotoxic.
Support for these studies came recently from brain sciences.
A recent review of the literature detected brain damages that might be targets of traffic-related air pollution.
Also, in the last two decades, many studies have shown that air pollution is associated with increased risk of psychotic experiences such as delusions or hallucinations in adolescents and adults, depression, anxiety and suicide in adults, and dementia in elderly.
However, the evidence is far from conclusive and there is little understanding of how inhaled pollutants gain access to the brain.
The reason for this is that findings from these observational studies that link air pollution with neurological and mental health problems cannot sort out what causes what.
It’s easy to find coincidental changes in the environment that correlate with the number of people receiving psychiatric diagnoses.
Due to environmental inequalities, people who live in more polluted areas tend to be different (e.g. in terms of ethnicity, gender or socioeconomic status) from those who live in less polluted areas in many ways not caused by the pollution, and it could be that one or more of these other differences the real cause of differences in rates of psychiatric disorders.
When analysing the data on this matter, statistical adjustments made by the researchers to try to allow for these other factors are not always adequate and some of them potential confounders have been estimated inadequately.
Conducting a randomised controlled trial — a type of scientific experiment that aims to reduce these type of biases (read more about these trials in a previous blog here) — could resolve this and establish a causal link between air pollution and mental health, but it would be unethical to subject people in high levels of air pollution as we would do, for example, in a pharmaceutical drug trial.
Furthermore, only one of the studies mentioned above investigates these associations over the lifetime of the participants, as ideally studies would wish to capture early life exposure in air pollution to provide a comprehensive understanding of how changes in individual cognitive development during childhood influence psychiatric symptoms in adulthood.
But, this is just the beginning…
We live in an era with unprecedented opportunities to harness on different types of data resources to answer the questions ahead of us.
Here at King’s College London, we are part of a wider international research community which aims to tackle these issues.
We recently had the ability to link high-resolution measures of air pollution with over 300,000 electronic mental health records from patients attending mental health services in South East London, and we are currently investigating for the first time the impact of air pollution in mental health service use and its associated costs over a period of over twelve years.
In addition, the UK supports an unparalleled collection of large-scale population-based studies which follow individuals from birth providing a wealth of information of measurements of air pollution and mental health data across the lifetime of the participants.
The advent of smartphone technologies has currently given us new opportunities to collect multiple environmental and mental health data. Specifically, via Urban Mind — a citizen-science project which uses a smartphone app to measure the experience of urban and rural living — we are currently investigating possible short-term associations between air pollution and mental wellbeing in real-time and as people go about their daily life.
Most importantly, residents in London, since January 2019, have been all participants of a natural experiment a kind of a clinical trial with the implementation of the new Ultra Low Emission Zone (ULEZ) — an extra daily change to those driving polluting vehicles in central London on top of the existing congestion charge.
ULEZ could act as the “therapeutic intervention” which aims to reduce harmful emissions from traffic, improve air quality and thus enhance the overall health of the population residing in the city, where improvements in mental health could also be possible and traceable.
The study of air pollution and health was originally driven by dramatic events such as the 1943 Los Angeles eye-stinging smog where L.A residents believed that the Japanese were attacking them with chemical welfare.
In Europe, the 1952 Great London Fog, in which a combination of water droplets with soot and sulphur from coal that powered industry and kept homes warm, resulted in thousands of deaths.
However, smog events did not remain only memories of the past.
In recent years, countries such as China, India and Nepal have been experiencing similar events and saw air pollution measurements reach record levels, conditions that led to significant increases in morbidity and mortality rates. Such events led to considerable debate with pressure from the media and the public which led towards policy (e.g., the UK 1956 Clean Air Act, the 1967 California Air Resources Board (CARB), the China 2015 Air Pollution Control Law) and heightened public awareness of the relationship between air quality and health.
In 2016, the World Health Organization (WHO) reported that 91% of the world’s population lives in places where air quality exceeds WHO guideline limits with 4.2 million of premature deaths being a result of ambient air pollution with 91% of these premature deaths occurring in low- and middle-income countries.
This is another example of environmental health inequalities at a global scale with current evidence from the research community indicating the need for revision of WHO air quality guidelines in even lower limits to protect human health.
There should be special attention for innovative measures to improve air quality such as the ULEZ, the introduction of buses and cars powered by electricity, and boldly rethink the way that we plan our cities — some cities have announced car-less visions, including Milan, Copenhagen, Madrid and Paris and Oslo.
Improving air quality is a tractable, though complex issue, and therefore measures to reduce air pollution may represent a potentially impactful and rare primary health measure for the prevention of psychiatric disorders, although we still need to learn much more about if and how this would work.
The Herbert Leroy Needleman story — both his showing the link between exposure to lead and deficits in children classroom performance, and the efforts from car industries to discredit his work — is one of the many stories that has taught us that air pollution, like climate change and structural inequalities, is not a problem to be resolved by science, but an issue deeply embedded into our individual and societal decisions and the power relations of our political systems.
Thus, we need to answer the question if we are willing to revert the neoliberal processes that generate these issues in favour of a better place to live in the future and bring this unhealthy love story to an end.
This blog was originally published on www.inspirethemind.org
NOTE FROM THE EDITORS: We are delighted to have Dr Ioannis Bakolis join our team of fantastic writers and share this piece. Dr Bakolis is a senior lecturer in Biostatistics and Epidemiology at the Institute of Psychiatry, Psychology and Neuroscience.
Ioannis is interested in how social, built and physical environments affect the epidemiology of both physical and mental health. Some of his current work includes exploring how exposure to road-traffic air and noise pollution affect mental disorders; and how neighbourhood deprivation relates to mental health over the life course.
Once again, a massive thank you from us to him for this great insight into the impact of air pollution on mental health!
