Recent research provides evidence that exposure to hot and cold temperatures during early life stages can have lasting effects on brain development, particularly affecting the white matter in the brain. A study published in the journal Nature Climate Change has found that children exposed to high or low temperatures, especially those living in poorer neighborhoods, show significant changes in the microstructure of their brain’s white matter.
Climate change poses a severe threat to human health, with its effects becoming increasingly evident as global temperatures rise. Children are particularly susceptible to the adverse effects of extreme temperatures due to their developing thermoregulation systems.
Previous studies have linked temperature variations to various health issues, including increased anxiety, depression, and aggressive behavior in children. However, the underlying structural brain changes due to these temperature exposures remained largely unexplored. This study aimed to fill that gap by investigating the potential impacts of heat and cold exposure on the white matter microstructure in children’s brains.
“Temperature impacts on human health are cause of concern for the scientific community and society, given the ongoing climate change emergency,” said study author Laura Granés, a medical doctor and predoctoral researcher at Bellvitge Biomedical Research Institute (IDIBELL) and at the Barcelona Institute for Global Health (ISGlobal).
“Childhood is a vulnerable period to environmental exposures, and the brain is particularly susceptible during early life. Although some studies had found an association between temperature and mental health/cognitive outcomes, no previous studies had assessed the potential effects of temperature on children’s brain.”
The researchers conducted their study within the framework of the Generation R Study, a long-term research project based in Rotterdam, the Netherlands. They recruited 9,896 pregnant women between April 2002 and January 2006, following their children from birth. For this specific study, 2,681 children aged 9 to 12 underwent brain magnetic resonance imaging (MRI) sessions to evaluate their white matter microstructure.
To assess temperature exposure, the researchers used the UrbClim model, which provides high-resolution hourly estimates of ambient temperature. They calculated the mean temperature over four-week periods from conception until the children’s MRI assessments. The average four-week mean temperature during the study period was 12.0 degrees Celsius (53.6 degrees Fahrenheit).
Cold and heat exposures were defined based on the temperature distribution during the study period. Cold exposure was defined as the 5th percentile of the monthly temperature distribution. This corresponds to a mean temperature of 2.6 degrees Celsius (36.7 degrees Fahrenheit). Heat exposure was defined as the 95th percentile of the monthly temperature distribution. This corresponds to a mean temperature of 20.2 degrees Celsius (68.3 degrees Fahrenheit).
White matter was analyzed using diffusion tensor imaging (DTI), focusing on two key metrics: mean diffusivity (MD) and fractional anisotropy (FA). These metrics help in understanding the density and organization of white matter tracts in the brain. Lower MD values and higher FA values typically indicate healthier white matter.
The study found that exposure to both cold and heat during early life was associated with significant changes in the microstructure of white matter. Specifically, cold exposure from the third month of pregnancy to the fifteenth month of life and heat exposure from the ninth month of life to 2.6 years of age were linked to higher global MD values at ages 9 to 12 years. Higher MD values indicate poorer white matter microstructure, which can affect neural connectivity and cognitive function.
“It is challenging to provide messages for the average person based on findings of one single study,” Granés told PsyPost. “I would say we need to be aware of the vulnerability of fetuses and children to these exposures in early life, but the solutions are not individual actions but public health policies for climate change adaptation and mitigation.”
Interestingly, the study did not find a significant association between temperature exposure and FA values. This suggests that while cold and heat may impact the overall diffusion properties of white matter, they might not affect its directional coherence to the same extent.
In a more detailed analysis, the researchers identified specific windows of susceptibility to temperature extremes. For cold exposure, these periods mostly spanned from pregnancy to the early years of life. For heat exposure, vulnerability periods were identified from around birth to three years of age in several white matter tracts, including the cingulum bundle, corticospinal tract, and superior longitudinal fasciculus.
Furthermore, the study revealed that children living in lower socioeconomic status (SES) neighborhoods were more vulnerable to the effects of temperature extremes. This finding underscores the importance of considering socio-economic factors when assessing the health impacts of climate change.
“It was interesting to see that there were some differences in the effects when we compared children living in neighborhoods with lower socioeconomic status vs those who were living in neighborhoods with a higher socioeconomic status, as we could see more effects in the first group,” Granés said. “Our hypothesis/interpretation of these findings is that these differences could be explained by poorer housing conditions or energy poverty (but this should be further investigated).”
While this study provides valuable insights, it has some limitations. One key limitation is the lack of indoor temperature data. Since children, especially infants, spend significant time indoors, indoor temperatures could differ significantly from outdoor estimates, potentially affecting the accuracy of the findings. Additionally, the study did not account for temperature exposures at daycare centers or schools, which could be relevant for older children.
“We are currently working on other projects to assess the impact of temperature exposure during childhood, considering other health outcomes such as brain function, behavior and psychological symptoms, and sleep quality,” Granés said.
The study, “Early life cold and heat exposure impacts white matter development in children,” was authored by Laura Granés, Esmée Essers, Joan Ballester, Sami Petricola, Henning Tiemeier, Carmen Iñiguez, Carles Soriano-Mas, and Mònica Guxens.
