Seven days of warm-water immersion enhances resting irisin and BDNF, but not klotho, in older men.
Level 4 - case-series / case-control
Uncontrolled single-arm before-and-after interventional study
PubMed 41779094 · doi:10.1113/EP093317
What was done
Twelve habitually active older men (median age: 68 years, IQR: 64–73) completed seven consecutive days of ~90-min warm-water immersion (~40°C), maintaining rectal temperature at ~38.5°C for the final 60 min. Before and after the 7-day protocol, participants performed a standardized exercise-heat stress test (three 30-min cycling bouts at 150, 200, and 250 W·m⁻²). Blood samples were taken at baseline and post-exercise to measure circulating BDNF, irisin, and klotho.
What was found
Warm-water immersion increased resting BDNF by 2.43 ng·mL⁻¹ (95% CI: 0.64–4.23; P = 0.005; 1.73-fold) and resting irisin by 0.94 ng·mL⁻¹ (95% CI: 0.25–1.63; P = 0.005; 1.65-fold). Resting klotho showed no significant change (mean difference: +0.05 ng·mL⁻¹; 95% CI: -0.05 to 0.14; P = 0.539). Exercise-induced acute changes in these cytoprotective hormones were not significant (P ≥ 0.053).
Why it matters
Repeated passive heat exposure can upregulate resting BDNF and irisin in older men, suggesting warm-water immersion could serve as a non-exercise stimulus for pathways supporting neurocognitive and metabolic health.
Limits
Small sample size (n = 12), limited entirely to habitually active older males, lacking a parallel control group, and with no direct assessment of long-term functional or clinical outcomes.
Cited by
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