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Ozone exposure linked to depression in adolescents

Ozone is a highly reactive gas that has molecules composed of three oxygen atoms (O3). It is a natural product found in the Earth’s upper atmosphere, the stratosphere, where it is very beneficial and helps to reduce the amount of harmful UV radiation that reaches Earth. However, ozone is also produced as a result of human activities in the lower levels of the atmosphere, the troposphere. This ground-level ozone is a toxic pollutant that we breathe in, and its levels are regulated by environmental laws.

Ozone is formed primarily when various pollutants from motor vehicle exhausts, power plants and other sources react in the presence of sunlight. It is a component of “smog” that is found in many large cities, but is also found in smaller cities and can be carried by the wind to almost any location. Higher levels of this gas have been linked to the occurrence of various physical ailments, including asthma, respiratory viruses and premature death from respiratory causes. 

Now, a new study from the American Psychological Association is the first to link exposure to ozone from pollution with an increase in depressive symptoms in adolescents, even in neighborhoods that meet air quality standards. Those symptoms include persistent feelings of sadness or hopelessness, difficulty with concentration, sleep disturbances, poor performance at school and thoughts about suicide. 

Past research attempting to identify environmental contributors to the development of depression have focused mainly on individual and family-level psychosocial characteristics, such as the quality of interpersonal relationships or socioeconomic resources. Very little research has been conducted into the possible role of pollution in the development of mental health issues.

“I think our findings really speak to the importance of considering air pollution’s impact on mental health in addition to physical health,” said lead researcher Dr. Erika Manczak, an assistant professor of psychology at the University of Denver.

The experts investigated whether levels of neighborhood ozone predicted the development of depressive symptoms over a four-year period in 213 adolescents (57 percent female; 53 percent male; of minority race/ethnicity). The average age of participants at the start was 11.4 years and they all lived in the San Francisco Bay area. The participants self-reported depressive and other types of psychopathology symptoms up to three times during the four-year period. 

In addition, their home addresses were used to obtain relevant ozone levels in their census tract, using data from air monitoring sites compiled by the California Environmental Protection Agency. Daily maximum eight-hour average concentrations of ozone for all air monitoring sites in California were extracted for the years 2012–2014 and the respective levels for each participants’ home address were used. Confounding variables, including personal, family, and neighborhood characteristics, were also assessed by the researchers.

The findings showed that adolescents who lived in areas with relatively higher ozone levels exhibited significant increases in depressive symptoms over time, even though the ozone levels in their neighborhoods didn’t exceed state or national air quality standards. The findings weren’t affected by the participants’ sex, age, race, household income, parental education, or the socioeconomic characteristics of their neighborhoods.

“It was surprising that the average level of ozone was fairly low even in the communities with relatively higher ozone exposure,” said Dr. Manczak. “This really underscores the fact that even low levels of ozone exposure have potentially harmful effects.”

Late childhood and early adolescence are times of physiological and emotional change, often associated with the onset of several forms of psychopathology. Thus, adolescents may be particularly vulnerable to the effects of ozone exposure at this stage. Furthermore, adolescents are exposed to more air pollution than are individuals in other age groups because they usually spend more time outside. 

Research by other scientists has shown that one of the ways in which ozone exposure may be linked to physical health is by activating immune processes. For example, inhaling ozone can contribute to both local and systemic inflammation; such inflammatory processes are also implicated in psychopathology symptoms, most importantly with those of depression. Research on animal models has also indicated that ozone exposure can disrupt neurotransmitter activity, promote greater oxidative stress, and lead to increased levels of inflammatory proteins

Although the authors acknowledge that this was a correlational study and does not prove a causal relationship between ozone exposure and the development of depression in adolescents, they do feel that it adds to a growing body of research implicating air pollution not only in physical health outcomes, but also in youth mental health outcomes. They feel it is important to consider environmental pollutants as possible causative factors, given that symptoms of depression in childhood and adolescence can be associated with life-long difficulties in psychosocial functioning

Because air pollution disproportionately affects marginalized communities, ozone levels could be contributing to health disparities, Manczak said. Communities also should consider ways to reduce ozone exposure, such monitoring the quality of the air in their homes, holding youth sporting events indoors when necessary and limiting driving and refueling during peak hours of air pollution. Investment in clean and renewable energy sources that reduce air pollution also could be helpful.

“I believe state and federal air quality standards should be stricter, and we should have tighter regulations on industries that contribute to pollution,” said Dr. Manczak. “Our findings and other studies suggest that even low levels of ozone exposure can pose potentially serious risks to both physical and mental health.”

The study is published in the journal Developmental Psychology.

By Alison Bosman, Staff Writer

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