Childhood behavioral problems and cortisol concentration in hair

A new study reveals that childhood behavioral problems are linked to a higher concentration of cortisol in the hair. This hormone secreted by the body in response to stressful situations accumulates in the hair and is an indicator of long-term stress.

Ane Arregi, a member of the B-EHRG (Basque Environmental Health Research Group) at the University of the Basque Country (UPV/EHU), has concluded in a study carried out on 11-year-old boys and girls from the INMA project that the greatest behavioural problems are related to higher levels of cortisol in the hair. The study also concludes that exposure to certain factors that can simultaneously cause chronic stress can determine the concentration of cortisol in the hair.

Cortisol is the hormone that the body secretes in response to stressful situations, and to analyse chronic stress, it is very useful to measure the concentration of cortisol in the hair. “Among other places, cortisol is usually found in the blood, saliva and urine, which indicates the level of cortisol at a given time: however, it accumulates in the hair and serves as an indicator of the degree of stress in the longer term, that is, chronic stress,” explains Ane Arregi Otxotorena, a researcher at the Faculty of Psychology at the University of the Basque Country. To distinguish between occasional stress and chronic stress, Arregi uses a clear example: “The stress that occurs when you go to buy bread one day and realise that you are short of money is not the same as the stress that occurs when you know that you do not have money to buy bread on a day-to-day basis.”

The B-EHRG researcher has used hair samples from 11-year-old boys and girls to assess chronic stress. The data for the research was taken from the INMA project: In the Childhood and Environment (INMA) project, a variety of data is collected from children and families to conduct long-term research from the mother’s pregnancy.

The research concludes that greater behavioural problems are related to higher cortisol levels in the hair. In addition, “we have seen that maternal stress is related to behavioural problems in boys and girls. This means that maternal stress can also influence children’s cortisol levels through their behavioural problems,” Arregi explained.

Ane Arregi. (Photo: UPV/EHU)

Environmental noise also influences cortisol levels

The authors of the study also found something they had not expected: “A higher level of 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 separated by sex, this relationship was only significant in boys.” According to the researchers, “initial acute stress caused by noise can lead to an increase in cortisol levels at one time, but chronic stress caused by long-term exposure to loud noise can reduce cortisol levels.” In order to confirm these unexpected noise-related results, they are going to carry out the same research in a larger European project, Athlete (Horizon 2020).

Environmental, social and individual factors

In general, “in our research we have detected these two factors, but that does not mean that there are no other related factors, but that we have not found any other relationship,” Arregi clarifies. “It is important to give a broader view to these investigations and at the same time take into account more than one factor that causes stress.” Thus, they have created a model to investigate the relationship between environmental, social and individual factors and the concentration of cortisol in children’s hair. As factors that can influence stress, they have taken into account all the factors that appear in the literature, such as green and blue spaces, air pollution, environmental noise, family and school relationships, the level of stress of parents, sleep problems, physical activity, age, sex, etc.

The researcher from the University of the Basque Country has pointed out that “there is still much to be investigated about the factors that influence cortisol levels in the hair of children and young people, and the studies carried out until now did not take into account the simultaneous influence of factors.” The model has been created with the aim of analysing precisely that. Arregi has explained that it is important to take into account many factors in the model: “From now on, the model will allow us to know which variables should be taken into account when measuring cortisol levels in hair and which should not.”

Future research should use this more complex approach to better understand the factors that determine cortisol concentration in children’s hair, since simultaneous exposure to environmental, social and individual factors can influence this concentration. Chronic stress in children is related to many health problems; “Childhood and adolescence are very vulnerable stages, because they are stages of rapid development. It is very important to know how different factors influence the health of children and adolescents at this stage so that they become healthy adults,” says the researcher.

“We believe that hair cortisol can be a very useful tool to assess the impact of environmental exposures on chronic stress. Ultimately, this can help implement effective public policies, because knowing what can cause chronic stress in the population of a place can make it easier to implement policies to prevent it,” she concluded.

This research is one of the studies published in the doctoral thesis of Ane Arregi Otxotorena. Arregi is not only a researcher in the B-EHRG group of the University of the Basque Country, but also a member of the BioGipuzkoa group of Environmental Epidemiology and Child Development.

The study is titled “Hair cortisol determinants in 11-year-old children: Environmental, social and individual factors”. It has been published in the academic journal Hormones and Behavior. (Source: UPV/EHU)