Introduction:
Winter swimming and sauna are supposed to beneficially affect the human organism, but there is still a lack of scientific evidence to confirm this phenomena.

Aim:
The aim of the study was to evaluate the effect of cold bath and sauna on markers of oxidative stress in the blood of experienced winter swimmers.

Material and Methods:
The study group consisted of 15 healthy men (volunteers), who spent 3 minutes in water at the temp. of +4 °C, followed by a 30 min sauna session – temp. 80 °C, relative humidity 15%. Blood samples were taken 4 times: before the cold bath (control), 5 and 30 min. after the cold bath (before sauna) and 5 min. after sauna. Activity of antioxidant enzymes – catalase (CAT) and superoxide dismutase (SOD), was determined in erythrocytes, glutathione peroxidase (GPx) in erythrocytes, and blood plasma, and ceruloplasmin (Cp) in serum. The level of lipid peroxidation products – thiobarbituric acid reactive substances (TBARS) and conjugated dienes (CD), were measured in erythrocytes and blood plasma.

Results:
An increase of GPx activity in plasma was observed directly after the cold bath, and also an increase of CD level was revealed after the changes in ambient temperature. The level of TBARS after winter swimming decreased both in erythrocytes and in blood plasma. After the sauna bath, TBARS concentration increased in plasma.

Conclusions:
The results provide evidence of constant alacrity of antioxidant system in prevention against harmful action of reactive oxygen species during exposition to changes in ambient temperature in experienced winter swimmers, which results in lack of damage on the cellular level. However, the use of sauna directly after a cold bath may be an additional source of oxidative stress.