Oxidative Stress, Testosterone, Cortisol, and Vitamin D: Differences in Professional Soccer Players of African and Caucasian Origin

Background: Under conditions of intense exercise, the production of free radicals and cortisol increases, whereas blood levels of testosterone and vitamin D decrease. The aim of the study was to evaluate the behavior of these parameters, ethnic differences, and their relationships with overtraining. Materials and Methods: Fifty professional soccer players were studied. Oxidative stress, testosterone, cortisol, and vitamin D were collected in pre- and mid-competitive season, and their differences in Africans and Caucasians were evaluated. Results: An increase in oxidative stress was observed in mid-season in both groups, but this was more significant in Africans (386 ± 162.6 vs. 277.8 ± 106.9 UCarr, p = 0.005; 2,965.4 ± 815.8 vs. 2,560.6 ± 608.1 BAP, p = 0.035). Levels of testosterone and vitamin D were higher in August compared to February in all participants; in both months, testosterone levels were higher in Africans (11.5 ± 2.4 vs. 9.1 ± 2.6, p = 0.004; 10.3 ± 1.6 vs. 7.7 ± 2.3, p = 0.000), whereas vitamin D levels were higher in Caucasians (39.4 ± 11.1 vs. 33.4 ± 9.7, p = 0.048; 31.8 ± 9.7 vs. 27.4 ± 9.4, in August and February, respectively). Insufficient/deficient levels of vitamin D were more frequently observed in Africans, but the difference was close to significance only in August. Conclusions: Although lower levels of vitamin D and higher levels of cortisol and oxidative stress in mid-season in Africans could have a negative influence on performance, no symptoms of overtraining were observed, probably due to higher levels of testosterone which enable homeostatic balance.