Early-life heat exposure increases risk of neurodevelopmental delay in preschool children

Early childhood represents a critical window of rapid brain growth and heightened vulnerability, yet the impacts of heat on development remain unclear. Here, using data from the Chinese National Cohort of Motor Development, comprising 101,228 children aged 3–5.5 years from 551 cities, we examined early-life exposure to ambient temperature. Within the observed range of 0–25 °C, we found that both prenatal and postnatal heat exposure were associated with increased risk of suspected neurodevelopmental delay. The exposure–response relationship followed a J-shaped pattern, with risk rising steeply at higher temperatures. Compared with the temperature of lowest risk, extreme heat (95th percentile) was linked to 35% higher risk during pregnancy and 53% higher risk from birth to age 3 years. Suspected neurodevelopmental delay risk increased across all examined heatwave definitions postnatally. These findings underscore the vulnerability of the developing brain to heat exposure and highlight the global relevance of temperature-related neurodevelopmental risks under climate change.