Children’s exposure to heat or cold can have lasting impacts on the brain

Exposure to spikes in either heat or cold in early childhood can have lasting effects on the microstructure of white matter in children’s brains, new research suggests. 

Published in Nature Climate Change the study highlights the vulnerability of children to extremes in temperature, and has led researchers to call for more to be done to respond to the threat posed by climate change. 

“The fibres of the white matter are responsible for connecting the different areas of the brain, enabling communication between them,” first author Laura Granés explained. 

“As the white matter develops, this communication becomes faster and more efficient. Our study is like a photograph at a particular moment in time and what we see in that image is that participants more exposed to cold and heat show differences in a parameter – the mean diffusivity – which is related to a lower level of maturation of the white matter.” 

In previous studies, she continued, these alterations have been associated with poorer cognitive function and certain mental health problems.

In the current ‘climate emergency’, researchers argue, the impact of extreme temperatures on human health is a major concern for the scientific community and society. Children are particularly vulnerable to temperature changes, as they have less ability to regulate their temperature. 

Over 2,500 children  from the Generation R Study, a birth cohort in Rotterdam, were included in the study, all of whom underwent magnetic resonance imaging (MRI) between 9 and 12 years of age. 

The MRI protocol assessed brain connectivity by measuring the magnitude and direction of water diffusion within the brain’s white matter. In more mature brains, water flows more in one direction than in all directions, which gives 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 until 8 years of age, and their effect on these MRI connectivity parameters (mean diffusivity and fractional anisotropy) measured at 9-12 years of age.

The results showed that children were most susceptible to brain changes from extremes in temperature from birth until three years of age.

“The largest changes in connectivity parameters are observed in the first years of life,” co-author Carles Soriano said. 

“Our results suggest that it is during this period of rapid brain development that exposure to cold and heat can have lasting effects on the microstructure of white matter.”

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

Children living in less advantaged neighbourhoods with higher levels of socioeconomic hardship were more likely to be vulnerable, authors continued, noting that in these children, the windows of susceptibility to cold and heat were similar to those identified in the overall cohort, but started earlier. 

These differences, they speculate, may be related to housing conditions and energy poverty.

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

To access the findings in full please see here.