RESUMEN
BACKGROUND: Exposure of the human body to cold water triggers numerous beneficial physiological changes. The study aimed to assess the impact of regular winter swimming on blood morphological, rheological, and biochemical indicators and activity of antioxidant enzymes in males. METHODS: The study involved 10 male winter swimmers (the same participants examined before the season and after the season) and 13 males (not winter swimming, leading a sedentary lifestyle) in the control group. Fasting blood was collected twice: in November and in March of the following year. Basic blood morphological indicators, red cell elongation index (EI) and aggregation index (AI), concentrations of testosterone, cortisol, urea, and creatinine, as well as plasma activity of antioxidant enzymes of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) were determined. RESULTS: The data were collected from the same winter swimmers at the beginning and end of the season. Winter swimming resulted in a significant increase of EI values at a shear stress of 0.30 (p = 0.40), 0.58 (p < 0.001), 4.24 (p = 0.021), 8.23 (p = 0.001), 15.59 (p = 0.001), 30.94 (p = 0.004), and 60.00 Pa (p = 0.043); haemoglobin was lower than before the season (p < 0.027). No significant changes were observed in AI, AMP, T1/2, the levels of urea, creatinine, eGFR, testosterone, cortisol, or the activity of CAT or SOD. There was a statistically significant increase in GPx activity (p = 0.014) and increase in testosterone concentration (p = 0.035) in the group of winter swimmers examined before the season as compared with the control group. No statistically significant differences were found for the mean values of blood morphological indicators and other parameters. CONCLUSIONS: Winter swimming can prove to be a health-promoting factor in males, as indicated by a rise in the deformability of red blood cells in the blood vessel system after a full season of winter swimming, leading to better body oxygenation, and improves the antioxidant defence and testosterone concentration (within standard limits) in the group of winter swimmers examined before the season as compared with the control group. Winter swimming helps maintain appropriate levels of blood rheological indicators, urea, creatinine, eGFR, cortisol, testosterone, and activity of antioxidant enzymes. TRIAL REGISTRATION: ClinicalTrials.gov identifier NCT06223087, 15.01.2024.