Exposure to cold or heat negatively affects mental health in adolescents

Two recently published studies by research teams at the Barcelona Institute for Global Health (ISGlobal) conclude that exposure to excessive temperatures leads to reduced brain connectivity and changes in behaviour. Using complementary approaches, the studies carried out by Mònica Guxens‘ group aim to highlight the consequences of climate change on adolescents.

Cold depresses and warmth deconcentrates

In one of the studies, in which behaviour was analysed, it was found that adolescents who were exposed to temperatures of around 5 °C for more than two months had internalising problems such as depression and anxiety. On the other hand, those who were exposed for two months to high temperatures (21.7 °C) suffered from attention problems. However, no cases were seen where both types of problems were present. This is because in neither case were the participants exposed to both high and low temperatures for long periods of time.

The analysis drew on data from the Generation R and INMA (Infancia y Medio Ambiente) projects, which involved almost 4000 adolescents in the Netherlands and 900 in Spain. Behaviours were determined through questionnaires, while the temperatures of their residential areas were determined with the high-precision UrbClim model, which has a resolution of 100 metres. That is, it reports temperatures every 100 metres over a given area. Notably, problems associated with cold were only seen in the Dutch cohorts, while those associated with heat were only detected in Spain.

“Mental health and climate change have not been a policy priority.”
Esmée Essers

Previous studies have already found that extreme temperatures trigger hospitalisations and other markers of mental health in adults. However, according to the paper’s first author, Esmée Essers, this study indicates that less severe symptoms linked to these temperatures can be detected earlier, in young people, when the effects may still be reversible. This could help to react to cases of mental health problems before they become too severe.

Heat disconnects brain networks

The second project studied the neurological effects of temperature and observed changes in the medial parietal and salience networks and the hippocaumpus.

The medial parietal network is associated with self-perception and autobiographical memory. The salience network is responsible for detecting internal and external stimuli and processing their information. In this sense, it is a very important network at a cognitive level. Finally, the hippocampus is involved in memory, learning and emotions.

The study showed that in pre-adolescents, all three networks were less connected when they had been exposed to temperatures between 18 and 24 °C in the days prior to the analysis. The loss of connection was more pronounced if the heat was just the day before. However, if the exposure had been to temperatures below 18°C, these networks remained unchanged.

As in the previous study, temperature data from the UrbClim model was used. This study involved 2229 participants from the Generation R project in the Netherlands who underwent functional magnetic resonance imaging (fMRI) when they were between 9 and 12 years old. In these, the oxygen consumption of different brain regions can be measured: the higher the oxygen consumption, the more neuronal activity. This allows researchers to know which regions are functioning synchronously. Reduced synchronisation of neural activity was seen in all three of these networks after exposure to heat in the previous days.

“We would like studies like ours to help promote climate change mitigation policies at both the European and local level”
Laura Granés

One of the hypotheses that first author Laura Granés and the rest of the research team are considering is that dehydration plays a fundamental role in the results obtained. It has been proven that children are more prone to dehydration during high temperatures than adults. Fluid loss could be one of the causes of the loss of functional connectivity in neural networks.

Previous studies have already found that low salience network connectivity in adolescents accentuates some symptoms of depression. This analysis has found one of the possible causes, which will help to alleviate it.

Data to tackle climate change

Esmée notes that the research could help promote new climate change mitigation policies that accentuate exposure to extreme temperatures. Laura says: ‘Our data show the importance of preventing children from experiencing heat stress”. Her work focused on exposure to temperatures at home and highlights that it shows the importance of building sustainably and insulating well. She adds that this does not mean abusing air conditioning, but rather finding ways to counteract the effects of heat.

Continuing with these lines of research is essential to mitigate the effects of climate change. Seeing if the results are repeated in other parts of the world or if the temperature difference affects other aspects of life will provide a global vision of the problem and tools to fight it.

The two research projects are part of the authors’ doctoral theses. Laura, who has already submitted her thesis, defends it in April, while Esmée expects to present it in July. Good luck to both!