Short- and long-term exposures to elevated temperatures influence weight status among young children: A secondary analysis of multi-longitudinal datasets from Australia and New Zealand.

Climate change and childhood obesity are major global health threats that share common upstream determinants. However, evidence on the associations between ambient temperature and childhood obesity remains limited. This study aimed to investigate the associations between temperature exposure and childhood obesity using longitudinal datasets from The Early Prevention of Obesity in CHildren (EPOCH) Collaboration. The analysis included four trials involving 2372 mother-child dyads from five cities in Australia and New Zealand (2007-2016). Anthropometric outcomes were assessed at ages 1, 2, 3.5, and 5 years, with overweight and obesity defined according to World Health Organization standards. Exposures to minimum, maximum temperatures, and extreme heat (>95th percentile of the maximum temperature) were assigned using residential postcode proximity to meteorological stations. Site-specific associations between temperature metrics and repeated anthropometric outcomes were estimated using Generalized Estimating Equations, adjusting for maternal and child socioeconomic factors. Random-effects meta-analyses were used to assess consistency across sites. Despite site-specific variation, meta-analyses showed that extreme heat was negatively associated with overweight in 3-month (RR =0.98, 95% CI: 0.97-0.99) and 6-month exposure windows. Obesity risk was increased with longer exposure (12-month) to elevated daily minimum temperature (RR =1.97, 95% CI:1.35-2.88) and maximum temperature. These findings suggest that short-term extreme heat may be associated with a lower risk of overweight, whereas long-term exposures to higher temperatures may be associated with a higher risk of childhood obesity. Early-life temperature exposures may be considered in obesity prevention under climate change.