Air pollution can send you mad! Linked to psychotic episodes in teens
Groan! Why does JAMA keep publishing these crap studies? Weak effects, dodgy statistics and failure to control for the most likely confounder. That summary of their work will probably grieve the authors but the fact remains that their study proves nothing. I suppose both the authors and the editors feel that their study is within convention but I am not interested in convention. I am interested in reliable evidence
So: they analysed their data using quartiles. That might sound very technical so let me spell it out: They threw away much of the information they had before they even started to analyse it! How does that sound? Unfortunately use of quartiles is quite a common procedure in medical research. Authors resort to it because using all the data would show no effect.
In this case they found the effect they expected only in the top quartile. It did not exist in the data as a whole. Expressing the relationship between illness and pollution as a Pearsonian correlation coefficient would almost certainly make that brutally clear. In their conclusions the authors did describe their findings accurately but the casual reader would almost certainly conclude that there was a overall correlation between psychiatric illness and air pollution. There was not.
And if there were, we would not know how to interpret it. Why? Because there was no control for income. Probably the most consistent finding in the whole of the epidemiological literature is that the poor have worse health. So you must control for income or your findings could be due to the target group on balance having worse health. Otherwise the lesser health you have found in that group could be simply a poverty effect. And there are reasons to think that was so in this case. The "teenagers living in areas of high pollution" could be living there because they were poorer. Well off people can usually avoid "living in areas of high pollution"
And given the weak effects reported, it's not only possible but probable that income was the sole influence at work in the data. Control for income would have knocked the effects down to negligibility
I know why they did not control for income: It is a more difficult datum to collect. But I usually controlled for it in my survey research career so it can be done if you want your findings to be taken seriously.
Sigh! Why do I so often have to spend an hour pointing all that stuff out? It's just Greenie cussedness. If they think a thing is so, they will twist the statistics to fit
Journal abstract appended
The first research ever to investigate the link between psychotic experiences and poor air quality found teenagers living in areas of high pollution suffered more than those in cleaner environments.
The researchers, from King's College London, used data from 2,232 children born in England and Wales.
They found that, overall, approximately a third of adolescents reported hearing or seeing something that wasn’t there, or feeling paranoid on at least one occasion between the ages of 12 and 18.
Such episodes, while not necessarily serious in themselves, can be a gateway to graver mental conditions such as schizophrenia.
The mental health data was compared against with hourly estimates of air pollution at their home addresses and two other locations where they spent a lot of time at the age of 17 such as a school.
"This study found that psychotic experiences were significantly more common among teens exposed to higher levels of air pollution," lead author Dr Joanne Newbury said.
"For example, teenagers exposed to the highest levels of nitrogen oxides had a 72 per cent greater odds for psychotic experiences compared to those with lower exposure.”
Adolescents exposed to the highest level of nitrogen dioxide had 71 per cent greater odds of having a psychotic experience, the study also found.
Meanwhile, those exposed to the highest levels of particulate matter, which can include carbon, liquids, metals and dust, had 45 per cent greater odds.
Previous research has shown a link between urban living and adolescent psychotic experiences, but the researchers said this is the first evidence of an association with air pollution levels.
Other studies have recently shown an association between dementia and air pollution levels, as well as strokes.
Some theories suggest that small particles from air pollution can enter the brain and cause inflammation or cause chemicals to enter the body, the researchers said.
The King's researchers said noise pollution may also play a role.
The paper is published in the journal JAMA Psychiatry.
Association of Air Pollution Exposure With Psychotic Experiences During Adolescence
Joanne B. Newbury et al.
Importance: Urbanicity is a well-established risk factor for clinical (eg, schizophrenia) and subclinical (eg, hearing voices and paranoia) expressions of psychosis. To our knowledge, no studies have examined the association of air pollution with adolescent psychotic experiences, despite air pollution being a major environmental problem in cities.
Objectives: To examine the association between exposure to air pollution and adolescent psychotic experiences and test whether exposure mediates the association between urban residency and adolescent psychotic experiences.
Design, Setting, and Participants: The Environmental-Risk Longitudinal Twin Study is a population-based cohort study of 2232 children born during the period from January 1, 1994, through December 4, 1995, in England and Wales and followed up from birth through 18 years of age. The cohort represents the geographic and socioeconomic composition of UK households. Of the original cohort, 2066 (92.6%) participated in assessments at 18 years of age, of whom 2063 (99.9%) provided data on psychotic experiences. Generation of the pollution data was completed on October 4, 2017, and data were analyzed from May 4 to November 21, 2018.
Exposures: High-resolution annualized estimates of exposure to 4 air pollutants—nitrogen dioxide (NO2), nitrogen oxides (NOx), and particulate matter with aerodynamic diameters of less than 2.5 (PM2.5) and less than 10 μm (PM10)—were modeled for 2012 and linked to the home addresses of the sample plus 2 commonly visited locations when the participants were 18 years old.
Main Outcomes and Measures: At 18 years of age, participants were privately interviewed regarding adolescent psychotic experiences. Urbanicity was estimated using 2011 census data.
Results: Among the 2063 participants who provided data on psychotic experiences, sex was evenly distributed (52.5% female). Six hundred twenty-three participants (30.2%) had at least 1 psychotic experience from 12 to 18 years of age. Psychotic experiences were significantly more common among adolescents with the highest (top quartile) level of annual exposure to NO2 (odds ratio [OR], 1.71; 95% CI, 1.28-2.28), NOx (OR, 1.72; 95% CI, 1.30-2.29), and PM2.5 (OR, 1.45; 95% CI, 1.11-1.90). Together NO2 and NOx statistically explained 60% of the association between urbanicity and adolescent psychotic experiences. No evidence of confounding by family socioeconomic status, family psychiatric history, maternal psychosis, childhood psychotic symptoms, adolescent smoking and substance dependence, or neighborhood socioeconomic status, crime, and social conditions occurred.
Conclusions and Relevance: In this study, air pollution exposure—particularly NO2 and NOx—was associated with increased odds of adolescent psychotic experiences, which partly explained the association between urban residency and adolescent psychotic experiences. Biological (eg, neuroinflammation) and psychosocial (eg, stress) mechanisms are plausible.
JAMA Psychiatry. Published online March 27, 2019. doi:10.1001/jamapsychiatry.2019.0056