The aim of the thesis was to determine the levels of 8-hydroxydeoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage, in the urine of individuals following a vegan diet. First morning urine samples were analyzed using an enzyme-linked immunosorbent assay (ELISA), and the obtained biomarker values were adjusted for urinary creatinine levels. Participants completed a survey with basic demographic and anthropometric data, and a three-day food record (two working days, one weekend day). An application was used to determine energy and nutrient intake on the basis of food consumption, and their association with 8-OHdG levels was examined. Concentrations ranged from 140.31 to 725.68 ng·mg-1 creatinine. No significant difference in median 8-OHdG levels was found between genders (334.50 vs. 213.48 ng·mg-1; p = 0.192). Correlation coefficients between age or BMI values of participants and their 8-OHdG concentrations were weakly positive, but not statistically significant. A slightly higher median urinary 8-OHdG was observed in non-smokers compared to smokers (334.50 vs. 222.54 ng·mg-1; p = 0.127). A statistically significant positive correlation was found with daily vegetable intake (r = 0.474; p = 0.035), while the association with coffee and tea intake was marginally significant (r = 0.419; p = 0.066). Food components whose intake was noticeably associated with 8-OHdG levels included alcohol (r = -0.599; p = 0.005), fiber (r = 0.430; p = 0.058), and protein (r = 0.442; p = 0.051). The results are consistent with the alternative hypothesis according to which higher levels of 8-OHdG in urine indicate more efficient DNA repair systems.