A link between common U.S. environmental toxins and depression symptoms has been revealed by scientists.
In a study of 3,427 adults from the National Health and Nutrition Examination Survey, researchers analyzed blood and urine samples, measuring levels of 27 toxins. A significant correlation was found between higher pollutant exposure and depression symptoms.
"This study adds to growing evidence linking environmental toxins to mental health problems, including depression. A related body of evidence, including my own research, links air pollutants, especially nitrogen dioxide and particular matter, to mental health problems in youth and adulthood, including psychosis and depression," Joanne Newbury, Sir Henry Wellcome Research Fellow at the University of Bristol, who did not work on the study, told Newsweek.
"The findings highlight the importance, from a public health and policy perspective, for considering the entire exposome when seeking to improve population mental health. Environmental toxins are potentially major area for intervention to improve mental health, which represents a growing burden around the world."
Out of 10 categories analyzed, the study identified six that contained toxic substances positively associated with depression.
These include acrylamide and glycidamide, ethylene oxide, two types of metals, three types of nicotine metabolites, six types of polycyclic aromatic hydrocarbons (PAHs) and 14 types of volatile organic compounds (VOC) metabolites.
In particular, individuals with detectable levels of MHBMA were found to have a 74 percent higher risk of depressive symptoms compared to those with undetectable levels. MHBMA is often measured as a biomarker to assess exposure to butadiene, which is a chemical commonly found in industrial emissions, cigarette smoke, and vehicle exhaust.
"We need better research and ways of measuring toxicants and responding to improve outdoor and indoor air quality, and regulate known harmful toxicants. Protecting people at critical periods of development, adolescence, pregnancy, when living with other health problems, is essential," Kamaldeep Bhui, a professor of psychiatry at the University of Oxford who did not work on the study, told Newsweek.
Additionally, higher levels of nicotine metabolites, substances produced when the body breaks down nicotine, were also linked to a greater risk of depression.
Specifically, chemicals TNE-2 and total hydroxycotinine were found to increase symptoms by 42 percent and 41 percent, respectively.
Newbury notes some limitations in the study, particularly its cross-sectional design and the absence of genetic information.
"The research does not show, for instance, if prior depression led participants to behaviors like smoking, which increased their exposure to toxins, nor whether genetics associated with depression and/or inflammation affects how people metabolize toxins," she said.
Men and younger individuals also appear to be more vulnerable to environmental toxins than women and older people, with 20 toxicants linked to symptoms in men and 23 in individuals aged 65 or below. This association was especially notable for nicotine and VOC metabolites.
However, Bhui cautioned, "I would approach the gender-specific findings with prudence."
"We need to understand specific mechanisms of the specific toxicants within each category, and also whether exposures were linked to occupation, indoor and outdoor environments, or selection biases of the women in the study, rather than reach for biological explanations.
"Although they might be relevant, they may be a little speculative from this type of study (as good as it is) with residual confounding and other potential biases. The perinatal period is also a vulnerable period for babies and mothers, and studies should look at this."
Crucially, the research also indicates that elevated levels of systemic inflammation, as measured by total white blood cell count, could be the crucial link between toxin exposure to depressive symptoms.
"We are becoming more aware of how air quality and pollution, and organic and inorganic particles in the air, can lead to poor general health, including depression and other mental illnesses, as well as affect neurodevelopment at critical phases of human growth such as adolescence," Bhui added.
"One mechanism is inflammation triggered directly by particles entering the body, but this process likely interacts with other adversities in the environment which are also associated with more inflammation."
As Newbury points out, the general population is often surprised to learn that pollutants and toxins can harm their mental health, emphasizing that increased public awareness is "definitely needed."
Generally, the public is not well-informed about emerging research such as this, except perhaps regarding efforts to reduce fuel emissions through diesel and low emission zones and carbon footprint reduction, Bhui said.
"We need more information on indoor and outdoor pollution, intoxicants and how to protect people across the lifespan," he said.
"This area of research has been largely neglected, for example, when trying to understand why some places like cities lead to poor health and why there are so many inequalities by place and demographics.
"Occupational exposures should also be considered, as well as protecting schools and hospitals and care homes, for example, from COVID and bioaerosols."
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