Background:
With regular cold baths, winter swimmers (individuals swimming in low-temperature water) develop adaptation to the cold. Apoptosis is a fundamental process of the immune system; its main role consists in maintaining cell homeostasis to prevent the development of pathological conditions. .This study focuses on a unique and interesting aspect of winter swimming, providing vital insights into the immune system's physiological adaptations to harsh environments. The study investigates a relatively under-researched area, the impact of winter swimming on leukocyte apoptosis, which is a novel and relevant contribution to the fields of sports physiology and immunology, as understanding how regular exposure to cold water influences immune cell apoptosis can provide broader insights into the human body's adaptive mechanisms to extreme environments.

Material and methods:
The study group consisted of 9 male winter swimmers. After a bath, blood samples were collected from the ulnar vein. Blood smears were stained with the Hemacolor method. By light microscopy (1000×) under immersion, apoptotic forms were counted in the whole preparation relative to 100 leukocyte forms.

Results:
Apoptotic leukocyte forms were very rare in the participants’ blood. Out of the 9 subjects, only 3 individuals exhibited 2–3% of leukocyte apoptotic forms.

Conclusions:
The findings demonstrate that low water temperature does not cause significant leukocyte apoptosis in winter swimmers, which is an important finding. This suggests that regular exposure to cold water may improve immunological resilience, which is a favourable adaptation for those who participate in this sport.