Cold and heat in childhood and development of cerebral white matter

In the current climate emergency situation, the impact of extreme temperatures on human health is one of the main concerns of the scientific community and society. The child population is especially vulnerable to temperature changes, since their thermoregulation mechanisms are still immature.

The results of a new study suggest that exposure to cold and heat in the first years of life can affect the development of the white matter of the brain. This underscores the vulnerability of fetuses and young children to extremes of cold and heat, and the need to protect the most vulnerable communities from the effects of global climate change.

Brain scans of more than 2,000 preteens specifically suggest that exposure to cold and heat early in life can have lasting effects on the microstructure of the brain’s white matter, especially when living in poor neighborhoods.

The study has been led by the Barcelona Institute for Global Health (ISGlobal) and the Bellvitge Biomedical Research Institute (IDIBELL), located in Hospitalet de Llobregat and which is one of the institutions NEAR the Generalitat of Catalonia. ERASMUS MC (Erasmus University Medical Center Rotterdam) in the Netherlands and the Center for Biomedical Research Network (CIBER) have also collaborated in their areas of Epidemiology and Public Health (CIBERESP), and Mental Health (CIBERSAM).

“We know that the developing brains of fetuses and children are particularly susceptible to environmental exposures, and there is some evidence that exposure to cold and heat can affect mental well-being and cognitive performance in children,” says Mònica Guxens, co-author of the study, researcher at ISGlobal, Erasmus MC and CIBERESP. “However, there is a lack of studies that evaluate possible changes in brain structure as a result of these exposures,” she adds.

In this study, the team of scientists analyzed the structure of white matter in the brains of preadolescents to identify windows of susceptibility to exposure to cold and heat in the first years of life. The analysis included 2,681 girls and boys from the Generation R Study, a birth cohort from Rotterdam, who underwent MRI between 9 and 12 years of age.

The MRI protocol assessed brain connectivity by measuring the magnitude and direction of water diffusion in the white matter of the brain. In more mature brains, water flows more in one direction than in all, giving lower values ​​for a marker called mean diffusivity and higher values ​​for another marker called fractional anisotropy.

The research team used an advanced statistical approach to estimate, for each participant, exposure to monthly mean temperatures from conception to age 8 years, and its effect on these MRI connectivity parameters measured at ages 9-12 years. .

The results show that exposure to cold during pregnancy and the first year of life, and exposure to heat from birth to 3 years of age were associated with greater mean diffusivity in preadolescence, which points to a maturation of the white matter slower.

Extreme exposure to cold (left) and heat (right) in the first years of life can affect the development of the white matter of the brain, according to the conclusions reached in the new study. (Images: Amazings/NCYT)

“The fibers of the white matter are responsible for connecting the different areas of the brain, which allows communication between them. As the white matter develops, this communication becomes faster and more efficient. Our study is like a photograph at a certain moment in time and what we see in that image is that the participants most exposed to cold and heat show differences in a parameter—mean diffusivity—that is related to a lower level of maturation of the white matter,” explains Laura Granés, researcher at IDIBELL and ISGlobal and first author of the study. “In previous studies, alteration of this parameter has been related to worse cognitive function and certain mental health problems,” she adds.

“The greatest changes in connectivity parameters are observed in the first years of life,” says Carles Soriano, co-author of the study and researcher at IDIBELL, the University of Barcelona (UB) and CIBERSAM. “Our results suggest that it is during this period of rapid brain development that exposure to cold and heat can have lasting effects on white matter microstructure.”

No association was found between temperature exposure in early life and fractional anisotropy at 9-12 years. The scientific team maintains that a possible explanation is that these two metrics reflect different microstructural changes, and that mean diffusivity may be a stronger indicator of white matter maturation, compared to fractional anisotropy.

An analysis stratified by socioeconomic conditions showed, as expected, that girls and boys living in poorer neighborhoods were more vulnerable to exposure to cold and heat. In these groups, the windows of susceptibility to cold and heat were similar to those identified in the general cohort, but began earlier. These differences may be related to housing conditions and energy poverty.

An important mechanism that could explain the effect of ambient temperature on neurodevelopment could be related to poorer sleep quality. Other possible mechanisms are alteration of placental functions, activation of the hormonal axis leading to increased cortisol production or inflammatory processes.

“Our findings help raise awareness about the vulnerability of fetuses and children to temperature changes,” says Guxens. The results also highlight the need to design public health strategies to protect the most vulnerable communities in the face of the imminent climate emergency.

The study is titled “Cold and heat exposure in early life and white matter microstructure in preadolescents.” And it has been published in the academic journal Nature Climate Change. (Source: IDIBELL)