A researcher from the Basque Environmental Health Research Group (B-EHRG) used hair samples from 11-year-old children to assess chronic stress. To conduct the study, she extracted data from the INMA project; the INMA (Environment and Childhood) project collects all kinds of data on children and families, starting with the mother’s pregnancy, for long-term studies.

So the research showed that, first, major behavioral problems are associated with higher levels of hair cortisol. In addition, “we saw that maternal stress is associated with children’s behavioral problems. This means that maternal stress can also affect children’s cortisol levels through their behavioral problems. In some way, in this two-step pathway,” Arregi explained.

Cortisol levels are also affected by ambient noise.

Second, they also found something they didn’t expect: “Higher exposure to environmental noise is associated with lower cortisol levels. We found that the higher the noise level, the lower the cortisol levels. When the analysis was stratified by gender, this association was significant only for boys.” According to the researchers, “initial acute noise stress can lead to a temporary increase in cortisol levels, but chronic stress caused by long-term exposure to high noise levels can lower cortisol levels.” To confirm the unexpected results regarding noise, the same research will be conducted as part of the broader European Athlete project (Horizon 2020).

Environmental, social and individual factors

In general, “in our study, we detected these two factors, but that does not mean that other factors are not related, but we did not find any other type of association,” Arregi explained. “It is important to give this study a broader perspective, taking into account more than one stressor.” So a model was created to examine the relationship between environmental, social and individual factors and children’s hair cortisol concentrations. All the factors that can affect stress and that appear in the literature were taken into account: for example, green and blue spaces, air pollution, environmental noise; family and school relationships, parental stress level; sleep problems, physical activity, age, gender, etc.

As the UPV/EHU researcher noted, “a lot remains to be studied regarding the factors influencing hair cortisol levels in children and adolescents, and studies have not yet considered the simultaneous influence of multiple factors.” The model was created to address this. Arregi explained that it is important to include multiple factors in the model: “From now on, the model will allow us to know which variables should be taken into account when measuring hair cortisol levels and which should not.”

Future studies will need to use this more complex approach to better understand the factors that determine hair cortisol in children; in fact, simultaneous exposure to various environmental, social and individual factors can affect hair cortisol concentrations. Children who are under chronic stress are associated with many health problems; “childhood and adolescence are very sensitive stages because they are stages of rapid development. It is very important to know how different factors affect the health of children and adolescents at this stage so that they can become healthy adults,” the researcher said.

“We believe that hair cortisol can be a useful tool in assessing the impact of environmental exposures on chronic stress. In short, it can help implement effective public policies; in fact, knowing what can cause chronic stress in a population in a specific location can facilitate the implementation of preventive policies,” she concluded.