Effect of cooling centres on BDNF and HSP70 responses during a simulated heatwave exposure in older adults

Cooling centres are widely recommended to protect older adults and other vulnerable populations from the heat. While there is emerging evidence that cooling centres limit physiological strain, limited data exist on their impact on biomarkers such as brain-derived neurotrophic factor (BDNF) and heat shock protein 70 (HSP70), which are implicated in stress adaptation and neuroprotection. We investigated the effects of a 2 h cooling intervention during a 9 h simulated heatwave on serum BDNF and HSP70 concentrations in older adults. Thirty-six adults aged 64-79 years were assigned to either a control group (n = 17) or a cooling group (n = 19). The cooling group rested in air-conditioning (∼23 °C) during hours 5-6, while controls remained in the heat (heat index: 37 °C). Serum BDNF and HSP70 were measured at baseline and end-exposure. Analysis of covariance (ANCOVA) was used to evaluate end-exposure biomarker concentrations, adjusting for baseline and physiological covariates, including thermal strain (area under the curve of core temperature), cardiovascular (heart rate, blood pressure), and autonomic function (root mean square of successive differences (RMSSD)). Cooling led to significantly lower end-exposure BDNF concentrations than controls (β = -595.0 pg/mL, 95% CI: -1162.7 to - 27.4, p = 0.041), while HSP70 remained unchanged (p = 0.779). BDNF was associated with thermal strain (β = 177.8 pg/mL per °C·h, p = 0.022), and RMSSD (β = 22.5 pg/mL per ms, p = 0.009). These findings demonstrate that a brief cooling break attenuates stress-related BDNF upregulation in older adults, with circulating BDNF reflecting cumulative thermal load and autonomic function rather than reduced neuroprotection. ClinicalTrials.gov identifier: NCT04353076.