Poor air quality is associated with a higher rate of multiple psychiatric disorders, new research suggests.
Analyzing large datasets from the United States and Denmark, the researchers found significant correlations between air pollution and bipolar disorder in both countries and between air pollution. and depression, schizophrenia and personality disorder in Denmark.
"If we know which environmental offenses can cause a disease, we can probably prevent it in some patients, especially if we know that they are genetically vulnerable." corresponding author Andrei Rzecki, Ph.D., professor of medicine and human genetics at the University of Chicago, Illinois, told Medscape Medical News.
The results were published online on August 20 in PLOS Biology.
A complex mix
Heredity largely explains the development of psychiatric disorders, but is "never 100%" and it is increasingly evident that environmental offenses play an important role, Rzecki said.
Air pollution is a complex mixture of small dust particles, gases, metals and organic pollutants generated by natural erosion of stones and materials created by man, vehicle exhausts, industrial activities and fires.
There is already evidence from humans, animals, and in vitro studies that air pollutants can enter the brain and are implicated in the etiology of neurological and psychiatric disorders.
For this study, researchers performed two analyzes, one using US data and the other Danish data
It was impossible to have the same design for the two datasets, Rzecki said. He added that the two countries have different cultures and different approaches to health care, population monitoring and environmental monitoring.
For US analysis, investigators use the IBM MarketScan Health Insurance Claims Database, which includes inpatient and outpatient claims, medical procedures and prescription drugs for more than 151 million patients, 2003 to 2013
Their analysis includes air, water and land quality (eg soil chemicals) and "built-in" environment (eg road traffic, transit access and pedestrian safety)
quantify for Air Pollution Researchers have used the Environmental Protection Agency's Air Quality Index, which is a summary measure of 87 potential air pollutants. Rzecki notes that for this analysis, researchers only measured air quality at one point and county level.
Researchers have transformed environmental projections into septics, with Q1 showing the best quality and Q7 showing the worst quality.
This analysis evaluated four psychiatric disorders – bipolar disorder, major depression, personality disorder and schizophrenia – and two neurological disorders – Parkinson's disease (PD) and epilepsy. Neurological disorders were included to act as controls, and "we did not expect to find an association," Rzecki says.
The results show that, compared to the best air quality, the worst air quality is associated with about a 27% increase in the incidence of bipolar disorder (95% confidence interval, 15% – 40%; P <10 -4 ).
In major depression there was an increase of 6% in the diagnosed frequency in the regions with the worst and best air quality.
Data in the United States also show a relationship between personality disorder and poor ground quality, but not air pollution.
There was no relationship between poor water quality or "built" environment and psychiatric illness, nor was there any relationship between any type of contamination and epilepsy or PD.
For the Danish analysis, researchers used national registers for treatment and contamination, which included more than 1.4 million people born from 1979 to 20 years 02 who lived in Denmark on the 10th birthday.
They examined the relationship between childhood exposure to air pollution and the same four psychiatric disorders included in the US analysis, but did not evaluate neurological disorders.
Researchers performed principal analyzes of components of 14 air quality indicators to obtain a summary measure of air pollution exposure. They again transform this exposure into septic matter, with Q1 representing the lowest exposure and Q7 the highest radiation.
With the Danish registers, researchers have been able to track the movements of each person over time and to access historical pollution data of 1 km with a 1 km cell size. This allowed them to evaluate exposure to air pollution at an individual level, which is "much more accurate" than the county-level exposure used in the US analysis, Rzecki said.
The results show that the incidence of all four psychiatric disorders increases with increasing levels of exposure to air pollution. The strongest association was in personality disorder, for which there was a 162% increase (95% confidence interval, 142% – 183%; P <2 × 10 −16 ) in percentage for category Q7 compared to category Q1.
In bipolar disorder, the prognosis is 24.3% higher in the Q7 group than in the Q1 group. Suspicious Pollutants
The sub-data include a "spatial dependence correction" that takes into account the proximity of US counties that may have a shared environment and the "harmonization" of the two datasets.
These additional analyzes  The most likely mechanism by which pollutants give rise to psychiatric illness is through neuroinflammation. "We have ample evidence of this from studies on eg, dogs, and anecdotal evidence in humans, "says Rzecki.
Researchers have noted that it is impossible to identify specific compounds in the air that can lead to mental illness; many pollutants are likely to contribute to the adverse effects on humans
However, there are "some suspects", including small particles of the environment, that can enter the lungs and bloodstream or pass through the nervous system. over the blood brain barrier, Rzecki said. "They can also pass through the olfactory system to the brain, which is a more direct route because we have olfactory neurons in our nose," he added.
He is convinced that stopping neuroinflammation can reverse psychiatric symptoms.
However, this needs to be verified, which can be challenging. Rzecki noted that clinical trials could not be conducted because it was "completely unethical" to expose people to poor environmental conditions for research purposes.
An Intriguing Opportunity
In an accompanying version, John PA Ioannidis, MD, Director, Prevention Research Center, Stanford University, California, and Director of the Meta-Research Innovation Center in Stanford, states that the cause and effect relationship is of air and mental illness is an "intriguing possibility" and that this study is a valuable contribution to this
Researchers "have offered a brilliant exploratory analysis with interesting hypotheses generating hints of bipolar disorder and possibly other psychiatric diagnoses", Ioannidis.
But he notes some shortcomings of the study, including the fact. that the "huge sample sizes of data sets" does not guarantee validity.
"Big data analysis can make absurd conclusions because of fundamental deficiencies in data quality," he writes. "The database in the US is approximately 100 times larger than that in Denmark, but the latter is of better quality."
Other notable differences include the differences between the datasets in the exposure measurements and the number of variables used for determination of air pollution.
In addition, the power of the observed associations is "modest"; although the effect sizes are larger in Denmark, they never reach relative risks greater than 3, notes Ioannidis.
"However, this is not necessarily a weakness. It is argued that most true causal effects are modest or even minor. / tiny; too large effects can simply indicate errors and biases, "he writes.
Researchers also" seem to interpret their results as being reproduced in different countries, "he writes." However, with the exception of bipolar disorder, point estimates are strikingly different. between the United States and Denmark, and the 95% confidence interval does not even overlap. "
It would be useful to carry out analyzes conducted by other researchers, including those who may have" skeptical views "on the association of air pollution, and
'Remarkable' bipolar findings
Comment on Medscape medical news Elizabeth Haaz, MD, Carson Tahoe Health, Carson City, Carson City, Carson City, Carson City, Carson City The American Psychiatric Association Climate Change Caucus said the study was interesting and that its illustrations were particularly impressive.
"Only the maps themselves showing the distribution of mood disorders and schizophrenia in the United States and the spread of healthy verbal media of different types is fascinating, "says Haase, who has not participated in the research.
She agreed with John nidis that the Danish analysis was "a little cleaner" than the US one, partly because it took into account exposure to child pollution. Early neuroinflammation or genetic damage in the early years could be an important risk factor for later pathology, she said.
Haase was also impressed by the way Danish data narrows the exposure to air pollution "up to 1 km, not from the whole county, which is much more specific."
She added that it was "remarkable" that the results of bipolar disorder are so consistent. She noted that no studies on bipolar disease and air pollution have been conducted so far. "It's a big shortfall in the field," she said.
Haaz emphasized that there are options for controlling air pollution that can reduce neuroinflammation. These include the production of clean energy, the control of industrial pollutants and the reduction of the use of fossil fuels.
There is "very clear evidence" that diseases are becoming less severe in areas of the US where coal plants are closed, she said.  The study was funded by NordForsk Project 75007, the DARPA Big Mechanism Program, the National Institutes of Health and a gift by Liz and Kent Douten. The authors of the study, Ioannidis and Haase did not consider the relevant financial relationships.
PLoS Biol. Published online August 20, 2019. Full Article, Revision
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