Effect of regular winter swimming on blood morphological, rheological, and biochemical indicators and activity of antioxidant enzymes in males.
Level 3 - non-randomized controlled study
Non-randomized prospective controlled cohort study with pre- and post-season measurements.
PubMed 38907310 · doi:10.1186/s13102-024-00932-3
What was done
Researchers evaluated 10 male winter swimmers before (November) and after (March) a winter swimming season and compared baseline measurements to 13 sedentary male controls. Fasting blood samples were analyzed for red blood cell elongation index (EI), aggregation index (AI), morphological parameters, testosterone, cortisol, renal markers (urea, creatinine, eGFR), and antioxidant enzyme activities (catalase [CAT], superoxide dismutase [SOD], and glutathione peroxidase [GPx]).
What was found
Winter swimming resulted in a statistically significant increase in red blood cell EI at shear stress levels of 0.58 Pa (p < 0.001), 4.24 Pa (p = 0.021), 8.23 Pa (p = 0.001), 15.59 Pa (p = 0.001), 30.94 Pa (p = 0.004), and 60.00 Pa (p = 0.043), with no significant change at 0.30 Pa (p = 0.40). Hemoglobin was significantly lower after the season (p < 0.027). No significant seasonal changes occurred in AI, AMP, T1/2, urea, creatinine, eGFR, testosterone, cortisol, CAT, or SOD. Compared to sedentary controls before the season, swimmers showed significantly higher GPx activity (p = 0.014) and testosterone concentration (p = 0.035).
Why it matters
This study provides preliminary human evidence that habitual seasonal cold-water swimming enhances red blood cell deformability without disrupting renal function markers or baseline cortisol levels.
Limits
The total sample size was very small (10 swimmers, 13 controls) and non-randomized. The control group consisted of sedentary individuals rather than active non-cold swimmers, confounding cold-water exposure with regular physical activity. Findings are restricted to males and may not generalize to females.