Exposure to high temperatures during pregnancy and early infancy is linked to slower growth of the thalamus later in childhood, according to research from the Barcelona Institute for Global Health (ISGlobal), supported by the “la Caixa” Foundation. Published in Environment International, the findings suggest that heat exposure during early life stages may have enduring effects on brain development.

Climate change is increasing worldwide exposure to extreme temperatures, raising concerns about children’s health impacts. Pregnancy and early childhood are critical periods for brain development, as the brain grows rapidly and remains sensitive to environmental factors. While prior research has connected heat exposure to changes in cognition and mental health, limited literature addresses effects on brain structure.

The study examined 3,251 children from the Generation R Study birth cohort in the Netherlands. Researchers used a high-resolution climate model providing weekly outdoor temperature estimates during pregnancy and monthly estimates from birth to 8.5 years of age. Brain MRI scans performed at approximately 10 and 14 years of age measured changes in 11 brain structures.

Among regions studied, only the thalamus showed consistent association with early-life heat exposure. The thalamus functions as the brain’s relay center, processing and transmitting sensory and motor information to the cerebral cortex. Researchers believe this region may be particularly sensitive because it develops very early in pregnancy and follows a strictly regulated developmental timeline.

The study identified a vulnerability period spanning pregnancy through the fifth month after birth. Compared with a reference temperature of 12.5°C, monthly mean temperatures of 20.5°C during this period were associated with slower thalamic growth between 9 and 15 years of age. No similar associations appeared for other brain structures or cold temperature exposure.

Slower thalamic growth was associated with more externalizing behavioral symptoms during adolescence, including aggressive and rule-breaking behavior, though no association with cognitive performance was found.

Possible biological mechanisms include heat exposure during pregnancy potentially altering maternal stress hormone levels, affecting the placenta’s ability to protect the developing fetus, or disrupting serotonin signaling. Heat-related inflammation and oxidative stress may also contribute, though further research is needed.

“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,” said Laura Granés, ISGlobal researcher.

“Future studies should investigate whether early-life heat exposure contributes to neurodevelopmental disorders and whether altered thalamic development could help explain these associations,” said Esmée Essers, ISGlobal co-author.

“With global temperatures continuing to rise, measures to reduce heat exposure during pregnancy and early infancy could play an important role in protecting children’s brain development,” said Mònica Guxens, ICREA Research Professor and study coordinator.

Journal: Environment International

DOI: 10.1016/j.envint.2026.110385

Article Title: “Early life ambient temperature and brain volumes change throughout childhood”

Publication Date: Volume 214 (110385), 2026

Source: Barcelona Institute for Global Health (ISGlobal)