Control of antioxidant supplementation through interview is not appropriate in oxidative-stress sport studies: Analytical confirmation should be required

Controlling antioxidant supplementation in athletes involved in studies related to oxidative stress and muscle damage is the key to ensure results. The aim of this study was to confirm through high-performance liquid chromatography (HPLC) analysis whether well-trained individuals lied during a personal interview when asked if they were taking supplements with antioxidants, and how this could affect oxidative stress, muscle damage, and antioxidant response.A total of 94 men, well trained in endurance sports, volunteered in this study. They denied taking any antioxidant supplementation at initial interview. After a HPLC analysis, abnormal α-tocopherol concentrations were detected, probably due to a hidden antioxidant supplementation. Participants were classified into two groups: no evidence of antioxidant supplementation (NS group = α-tocopherol values <80 nmol/mL; n = 75) and evidence of antioxidant supplementation (S group = α-tocopherol values >80 nmol/mL; n = 19). Lipid peroxidation, muscle damage, antioxidant enzyme activity, and nonenzymatic antioxidant content were analyzed according to this classification. Statistical comparisons were performed using Student's t test.The α-tocopherol concentrations were significantly higher in the S group than in the NS group (MD = 725.01 ± 39.01 nmol/mL; P = 0.001). The S group showed a trend toward lower hydroperoxides than the NS group (MD = 1.19 ± 0.72 nmol/mL; P = 0.071). The S group showed significantly lower catalase activity than the NS group (MD = 0.10 ± 0.02-seg-1 mg-1; P < 0.01). Skeletal muscle damage markers did not differ between experimental groups.Data from the present study reveal that 20% of participants lied in the exclusion criteria of antioxidant supplementation in a personal interview, as they showed high plasmatic α-tocopherol concentrations after HPLC verification. Catalase activity seems to be affected by high α-tocopherol plasma levels. Therefore, we strongly recommend the HPLC analysis as a necessary tool to verify the antioxidant intake and preserve results in studies linking oxidative stress and sport.