Heat Exposure During Pregnancy and Infancy May Influence Children’s Brain Development

Physical activity, Exposure to high temperatures during pregnancy and early infancy is associated with slower growth of the thalamus later in childhood, according to a study led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by the ”la Caixa” Foundation. The findings, published in Environment international, suggest that heat exposure during the earliest stages of life may have lasting effects on brain development.

Climate change is increasing exposure to extreme temperatures worldwide, raising concerns about its impact on children's health. Pregnancy and the first years of life are particularly important for brain development, as the brain grows rapidly and is especially sensitive to environmental factors. Although previous studies have linked heat exposure to changes in cognition and mental health, there is not much literature about its effects on brain structure.

"We wanted to examine whether exposure to heat or cold from conception to 8.5 years of age was associated with changes in brain development during late childhood and adolescence, and to identify the periods when the brain is most vulnerable," explains Laura Granés, ISGlobal and IDIAPJGol researcher and first author of the study.

The study included 3,251 children participating in the Generation R Study, a birth cohort in the Netherlands. “We used a high-resolution climate model that provided weekly outdoor temperature estimates during pregnancy and monthly estimates from birth to 8.5 years of age at each participant's place of residence. We then analysed brain MRI scans performed at around 10 and 14 years of age”says Granés. This allowed researchers to measure how the volume of 11 brain structures changed over time and to examine whether these changes were associated with earlier exposure to heat or cold.

Why the thalamus appears especially vulnerable

Among the brain regions studied, only the thalamus showed a consistent association with early-life heat exposure. The thalamus acts as the brain's main relay centre, processing and transmitting sensory and motor information to the cerebral cortex.

The researchers believe this region may be particularly sensitive because it develops very early in pregnancy and follows a tightly regulated developmental timeline. Its rich blood supply during foetal development may also make it more vulnerable to heat-related changes affecting the placenta or blood flow to the foetus.

A critical window: from conception to the fifth month of life

The study identified a clear period of vulnerability spanning pregnancy and the first months after birth. Compared with a reference average temperature of 12.5°C, exposure to monthly mean temperaturesof 20.5°C during this period (calculated across day and night) was associated with slower thalamic growth between 9 and 15 years of age. No similar associations were found for other brain structures or for exposure to cold temperatures.

How heat could affect brain development

Although the study was not designed to identify the biological mechanisms involved, previous research suggests several possible explanations. Heat exposure during pregnancy may alter maternal stress hormone levels, affect the placenta's ability to protect the developing foetus from these hormones, or disrupt serotonin signalling, which plays an important role in the formation of connections between the thalamus and the cerebral cortex. Heat-related inflammation and oxidative stress may also contribute, although more research is needed to confirm these mechanisms.

The researchers also found that slower thalamic growth was associated with more externalising behavioural symptoms during adolescence, including aggressive and rule-breaking behaviour. However, they did not find an association with cognitive performance. "Future studies should investigate whether early-life heat exposure contributes to neurodevelopmental disorders and whether altered thalamic development could help explain these associations," says Esmée Essers, ISGlobal researcher and study co-author.

"The children who participated in our study were born between 2002 and 2006. Since global temperatures have continued to rise, it would be valuable to conduct a new study under current conditions. In any case, our findings suggest that taking measures to reduce heat exposure during pregnancy and early infancy could play an important role in protecting children's brain development," concludes Mònica Guxens, ICREA Research Professor in ISGlobal and coordinator of the study.

Reference: Granés, L., Essers, E., Kusters, M. S. W., Petricola, S., Tiemeier, P. H., Soriano-Mas, P. C., Schwartz, P. J., & Guxens, P. M. (2026). Early life ambient temperature and brain volumes change throughout childhood. Environment International, 214(110385), 110385. https://doi.org/10.1016/j.envint.2026.110385

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