Whole-Body Cryotherapy at −90 °C for 9 Weeks: Effects on Immune Function, Stress, and Immune-Related and Vascular Blood Parameters in Healthy Adults – Results of an Exploratory One-Armed Pilot Study

Background/Objectives: Whole‑body cryotherapy (WBC), a brief exposure to extreme cold (−90 °C), has been proposed to modulate immune, metabolic, and stress‑related pathways. This exploratory one‑armed pilot study investigated the effects of an 18‑session WBC protocol on immune markers, body composition, and perceived stress in healthy adults. Methods: Nineteen participants (mean age 52.9 ± 9.8 years) completed 18 WBC sessions over 9 weeks (3–6 minutes each), followed by a 9‑week follow‑up. Assessments were performed at baseline (M1), post‑intervention (M2), and follow‑up (M3). Primary outcomes included immune parameters (lymphocytes, granulocytes, cytokines, soluble ACE2), body composition (waist circumference, water compartments, lean mass), and perceived stress (Trier Inventory for Chronic Stress, TICS). Results: Waist circumference decreased from 83.8 ± 5.7 cm (M1) to 80.2 ± 4.2 cm (M2) (p = 0.001; M1 vs M2; p = 0.004). Total body water (p = 0.008), lean body mass (p = 0.008), intracellular water (p = 0.005), and extracellular water (p = 0.021) also showed time-dependent effects. Immune modulation included increased lymphocytes (25.6 ± 7.1% to 29.3 ± 8.3%, p = 0.012) and decreased granulocytes (63.5 ± 6.8% to 58.7 ± 7.9%, p = 0.011) at M2. Anti‑inflammatory IL‑10 (virus‑stimulated) rose markedly (33.5 ± 29.3 to 63.5 ± 50.5 pg/mL, p < 0.001), while IFN‑γ (virus‑stimulated) increased over time (p = 0.031). Soluble ACE2 decreased at follow‑up (0.5 ± 0.7 to 0.3 ± 0.4 ng/mL, p = 0.029). Perceived stress improved in several TICS domains, including Work Overload (p = 0.009) and Pressure to Succeed (p = 0.018). Conclusions: This pilot study demonstrates that repeated WBC at −90 °C induces measurable changes in immune regulation, body composition, and perceived stress. These findings support the feasibility and potential physiological relevance of WBC and providing effect‑size estimates for future randomized controlled trials.