Effect of pedestal fan use on serum stress biomarkers in older adults exposed to simulated daylong indoor overheating

Abstract

There is an urgent need to develop targeted heat-alleviation strategies to protect heat-vulnerable older adults. We have shown that electric fan use had nominal impact on reducing body core temperature and cardiovascular strain during daylong exposure to simulated indoor overheating. Here, we examined the effects of pedestal fan use during exposure to hot conditions on systemic markers of enterocyte damage, immune activation, renal ischemia, and inflammation in older adults. Eighteen adults (8 females; age 72, SD 7 years) underwent 3 randomized 8-h exposures to 36°C, 45% relative humidity seated in front of a fan delivering air speeds of 0 m/s (control), 2 m/s (normal air speed delivered by electric fans), or 4 m/s (air speed used in biophysical modeling). Body core temperature and cardiovascular strain were measured throughout. Blood samples were obtained for analysis of systemic biomarkers before and at the end of exposure. End-exposure core temperature was elevated ~1.0°C from baseline in all conditions. Following heat exposure, IFABP increased by 364 pg/mL [95% CI: 59, 670; p = 0.02] and LBP increased by 3.06 ng/mL [1.12, 5.00; p = 0.002] but was not different between the fan use and control condition (all p ≥ 0.15). No changes were observed for sCD14, IL-6, TNFα, CRP, or NGAL (all p ≥ 0.15). The use of electric fans during daylong exposure to indoor overheating failed to meaningfully mitigate increases in physiological strain or biochemical markers associated with enterocyte damage and immune activation in older adults. ClinicalTrials.gov identifier: NCT05695079.

Keywords: aging; climate change; electric fans; enterocyte damage; immune response; inflammation.

FIGURE 1

Flow of participants through the study. A CONSORT diagram depicting participant enrollment, randomization, and analysis. Out of 23 individuals screened for eligibility, 18 adults were enrolled. All completed 3, randomized 8 h heat exposures with: No cooling (control), fan at 2 m/s, or fan at 4 m/s.

FIGURE 2

Body core temperature (a), the change in body core temperature (b), mean skin temperature (c) and heart rate (d) throughout the 8‐h heat exposure during the control condition (open white circles), 2 m/s fan condition (light gray squares), and 4 m/s fan condition (dark gray triangles) in 18 older adults. Data show the mean and 95% confidence intervals. The insets illustrate the individual difference in responses between the control and 2 m/s condition, and control and 4 m/s condition. The dashed line demarks the point of no difference, and the cross represents the group mean and 95% confidence interval.

FIGURE 3

Absolute concentrations of serum intestinal fatty acid binding protein (IFABP; a), soluble cluster of differentiation 14 (sCD14; c) and lipopolysaccharide binding protein (LBP; e) at baseline and at the end of the 8‐h exposure to 36°C, 45% RH. Baseline‐corrected changes in IFABP (b), sCD14 (d) and LBP (f) before and after the control condition, fan at 2 m/s condition, and fan at 4 m/s condition. Solid lines denote individual participant responses. Summary statistics are presented as the group mean and standard deviation. Individual data are shown for 18 participants. The baseline‐corrected end‐exposure changes in IFABP (b), sCD14 (d) and LBP (f) are presented relative to the no fan control condition. Summary statistics are presented as the group mean and standard deviation.

FIGURE 4

Absolute concentrations of plasma interleukin‐6 (IL‐6; a), tumor necrosis factor alpha (TNFα; c), C‐reactive protein (CRP; e), and neutrophil gelatinase‐associated lipocalin (NGAL; g) at baseline and at the end of the 8‐h exposure to 36°C, 45% RH. Solid lines denote individual participant responses. Summary statistics are presented as the group mean and standard deviation. Baseline corrected changes in IL‐6 (b), TNFα (d), CRP (f), and NGAL (h) before and after the control condition, fan at 2 m/s condition, and fan at 4 m/s condition. Individual data are shown for 18 participants. The baseline corrected end‐exposure changes in IL‐6 (b), TNFα (d), CRP (f), and NGAL (h) are presented relative to the no fan control condition. Summary statistics are presented as the group mean and standard deviation.